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Answers of Science NCERT solutions for class 10 Chapter 13 Magnetic effects of electric current

Chapter 13

Magnetic Effects of Electric Current

In-Chapter Exercise

Question 1:

Why does a compass needle get deflected when brought near a bar magnet? 

Answer:

A compass needle is a small bar magnet. When it is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle  shows a deflection when brought near the bar magnet.

In-Chapter Exercise

Question 1:

Draw magnetic field lines around a bar magnet. 

Answer:

Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.

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*Question 2:

List the properties of magnetic lines of force.

Answer:

The properties of magnetic lines of force are as follows.

  1. Magnetic field lines emerge from the north pole.
  2. They merge at the south pole.
  3. The direction of field lines inside the magnet is from the south pole to the north pole.
  4. Magnetic lines do not intersect with each other.

*Question 3:

Why don’t two magnetic lines of force intersect each other? 

Answer:

If two field lines of a magnet intersect, then at the point of intersection, the compass needle points in two different directions. This is not possible. Hence, two field lines do not intersect each other.

In-Chapter Exercise

*Question 1:

Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Answer:

Inside the loop = Pierce inside the table

Outside the loop = Appear to emerge out from the table

For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.

*Question 2:

How much energy is given to each coulomb of charge passing through a 6 V battery? 

Answer:

The energy given to each coulomb of charge is equal to the amount of work required to move it. The amount of work is given by the expression,

Potential difference =

lCFRaNVeMUx3nrtWyqaNgwlOscLl2SqnbYIRSryADtjvHJFrVBZIrn5nep2c5wGWsIx7te Az PewjeNlUaX1gz05yK v77qS3l42b5uVfzI Q2fw1SdAMYV8RFG VnQqiEuGo

Where, Charge = 1 C

Potential difference = 6 V
HYygk8o8UXlUfcr3uVJc3Er3YrWfYvcLwdF1YsVnADnAfnieN2bNQa6ScFvA5mpZIUYKlKXQI2KgJLvGTjZrXMEKTFi6V8ifGxHOdcxro1cCvc0Xnic7Sau12gYh lY MbqK25E

Therefore, 6 J of energy is given to each coulomb of charge passing through a battery of 6 V.

*Question 3:

Choose the correct option.

The magnetic field inside a long straight solenoid-carrying current

  1. is zero
  2. decreases as we move towards its end
  3. increases as we move towards its end
  4. is the same at all points 

Answer:

(d)The magnetic field inside a long, straight, current-carrying solenoid is uniform. It is the same at all points inside the solenoid.

In-Chapter Exercise

Question 1:

Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

  1. mass
  2. speed
  3. velocity
  4. momentum 

Answer:

(c) and (d)

When a proton enters in a region of magnetic field, it experiences a magnetic force. As a result of the force, the path of the proton becomes circular. Hence, its velocity and momentum change.

*Question 2:

How do we think the displacement of rod AB will be affected if (i) current in rod AB is increased: (ii) a stronger horse-shoe magnet is used: and (iii) length of the rod AB is increased?

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Answer:

A current-carrying conductor placed in a magnetic field experiences a force. The magnitude of force increases with the amount of current, strength of the magnetic field, and the length of the conductor. Hence, the magnetic force exerted on rod AB and its deflection will increase if

  1. current in rod AB is increased
  2. a stronger horse-shoe magnet is used
  3. length of rod AB is increased

*Question 3:

A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is

(a) towards south (b) towards east

  1. downward (d) upward 

Answer:

The direction of the magnetic field can be determined by the Fleming’s left hand rule. According this rule, if we arrange the thumb, the centre finger, and the fore finger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field. Since the direction of positively charged alpha particle is towards west, the direction of current will be the same i.e., towards west. Again, the direction of magnetic force is towards north. Hence, according to Fleming’s left hand rule, the direction of magnetic field will be upwards.

In-Chapter Exercise

Question 1:

State Fleming’s left-hand rule. 

Answer:

Fleming’s left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.

Question 2:

What is the principle of an electric motor? 

Answer:

The working principle of an electric motor is based on the magnetic effect of current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is given by the Fleming’s left-hand rule.

*Question 3:

What is the role of the split ring in an electric motor? 

Answer:

The split ring in the electric motor acts as a commutator. The commutator reverses the direction of current flowing through the coil after each half rotation of the coil. Due to this reversal of the current, the coil continues to rotate in the same direction.

In-Chapter Exercise

Question 1:

Explain different ways to induce current in a coil. 

Answer:

The different ways to induce current in a coil are as follows:

  1. If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
  2. If a magnet is moved relative to a coil, then an electric current is induced in the coil.

In-Chapter Exercise

Question 1:

State the principle of an electric generator. 

Answer:

An electric generator works on the principle of electromagnetic induction. It generates electricity by rotating a coil in a magnetic field.

*Question 2:

Name some sources of direct current. 

Answer:

Some sources of direct current are cell, DC generator, etc.

*Question 3:

Which sources produce alternating current? 

Answer:

AC generators, power plants, etc., produce alternating current.

*Question 4:

Choose the correct option.

A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

(a) two revolutions (b) one revolution

(c) half revolution (d) one-fourth revolution 

Answer:

(c) When a rectangular coil of copper is rotated in a magnetic field, the direction of the induced current in the coil changes once in each half revolution. As a result, the direction of current in the coil remains the same.

In-Chapter Exercise

Question 1:

Name two safety measures commonly used in electric circuits and appliances. 

Answer:

Two safety measures commonly used in electric circuits and appliances are as follows:

  1. Each circuit must be connected with an electric fuse. This prevents the flow of excessive current through the circuit. When the current passing through the wire exceeds the maximum limit of the fuse element, the fuse melts to stop the flow of current through that circuit, hence protecting the appliances connected to the circuit.
  2. Earthing is a must to prevent electric shocks. Any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.

*Question 2:

An electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.

Answer:

Current drawn by the electric oven can be obtained by the expression,

P = VI

Where, Current = IiqywjDX5ABqT36xxxyVpgl9XzzK1k6VU9re

Power of the oven, P = 2 kW = 2000 W Voltage supplied, V = 220 V6qqyIapWvErEUIyaWhynVkpuRIn YUx4THyXsKEV5mGSghK mat7dm9CyojIKCBsT29sFq0yeNPfFEEajgZ4zr0AeTIxczv37r RUkCrsDbZHrk 1wrwJeZf3uYsVFrsabeSVQ

Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.

Question 3:

What precaution should be taken to avoid the overloading of domestic electric circuits? 

Answer:

The precautions that should be taken to avoid the overloading of domestic circuits are as follows:

  1. Too many appliances should not be connected to a single socket.
  2. Too many appliances should not be used at the same time.
  3. Faulty appliances should not be connected in the circuit.
  4. Fuse should be connected in the circuit.

Last Exercise

*Question 1:

Which of the following correctly describes the magnetic field near a long straight wire?

  1. The field consists of straight lines perpendicular to the wire
  2. The field consists of straight lines parallel to the wire
  3. The field consists of radial lines originating from the wire
  4. The field consists of concentric circles centred on the wire

Answer:

(d) The magnetic field lines, produced around a straight current-carrying conductor, are concentric circles. Their centres lie on the wire.

*Question 2:

The phenomenon of electromagnetic induction is

  1. the process of charging a body
  2. the process of generating magnetic field due to a current passing through a coil
  3. producing induced current in a coil due to relative motion between a magnet and the coil
  4. the process of rotating a coil of an electric motor 

Answer:

(c) When a straight coil and a magnet are moved relative to each other, a current is induced in the coil. This phenomenon is known as electromagnetic induction.

Question 3:

The device used for producing electric current is called a

  1. generator
  2. galvanometer
  3. ammeter
  4. motor 

Answer:

(a) An electric generator produces electric current. It converts mechanical energy into electricity.

*Question 4:

The essential difference between an AC generator and a DC generator is that

  1. AC generator has an electromagnet while a DC generator has permanent magnet.
  2. DC generator will generate a higher voltage.
  3. AC generator will generate a higher voltage.
  4. AC generator has slip rings while the DC generator has a commutator. 

Answer:

(d) An AC generator has two rings called slip rings. A DC generator has two half rings called commutator. This is the main difference between both the types of generators. 

*Question 5:

At the time of short circuit, the current in the circuit

  1. reduces substantially
  2. does not change
  3. increases heavily
  4. vary continuously 

Answer:

(c) When two naked wires of an electric circuit touch each other, the amount of current that is flowing in the circuit increases abruptly. This causes short-circuit.

Question 6:

State whether the following statements are true or false.

  1. An electric motor converts mechanical energy into electrical energy.
  2. An electric generator works on the principle of electromagnetic induction.
  3. The field at the centre of a long circular coil carrying current will be parallel straight lines.
  4. A wire with a green insulation is usually the live wire of an electric supply.

Answer:

  1. False

An electric motor converts electrical energy into mechanical energy.

  1. True

A generator is an electric device that generates electricity by rotating a coil in a magnetic field. It works on the principle of electromagnetic induction.

  1. True

A long circular coil is a long solenoid. The magnetic field lines inside the solenoid are parallel lines.

  1. False

Live wire has red insulation cover, whereas earth wire has green insulation colour in the domestic circuits.

Question 7:

List three sources of magnetic fields. 

Answer:

Three sources of magnetic fields are as follows:

  1. Current-carrying conductors
  2. Permanent magnets
  3. Electromagnets

*Question 8:

How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.

Answer:

A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure.

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In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.

Question 9:

When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

Answer:

The force experienced by a current-currying conductor is the maximum when the direction of current is perpendicular to the direction of the magnetic field.

Question 10:

Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

Answer:

The direction of magnetic field is given by Fleming’s left hand rule. Magnetic field inside the chamber will be perpendicular to the direction of current (opposite to the direction of electron) and direction of deflection/force i.e., either upward or downward. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.

*Question 11:

Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

Answer:

An electric motor converts electrical energy into mechanical energy.

It works on the principle of the magnetic effect of current. A current-carrying coil rotates in a magnetic field. The following figure shows a simple electric motor.

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When a current is allowed to flow through the coil MNST by closing the switch, the coil starts rotating anti-clockwise. This happens because a downward force acts on length MN

and at the same time, an upward force acts on length ST. As a result, the coil rotates anti-clockwise.

Current in the length MN flows from M to N and the magnetic field acts from left to right, normal to length MN. Therefore, according to Fleming’s left hand rule, a downward force acts on the length MN. Similarly, current in the length ST flows from S to T and the magnetic field acts from left to right, normal to the flow of current. Therefore, an upward force acts on the length ST. These two forces cause the coil to rotate anti-clockwise.

After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.

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The current flows through the coil in the direction TSNM. The reversal of current through the coil MNST repeats after each half rotation. As a result, the coil rotates unidirectional. The split rings help to reverse the direction of current in the circuit. These are called the commutator.

Question 12:

Name some devices in which electric motors are used? 

Answer:

Some devices in which electric motors are used are as follows:

  1. Water pumps
  2. Electric fans
  3. Electric mixers
  4. Washing machines

*Question 13:

A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

Answer:

A current induces in a solenoid if a bar magnet is moved relative to it. This is the principle of electromagnetic induction.

  1. When a bar magnet is pushed into a coil of insulated copper wire, a current is induced momentarily in the coil. As a result, the needle of the galvanometer deflects  momentarily in a particular direction.
  2. When the bar magnet is withdrawn from inside the coil of the insulated copper wire, a current is again induced momentarily in the coil in the opposite direction. As a result, the needle of the galvanometer deflects momentarily in the opposite direction.
  3. When a bar magnet is held stationary inside the coil, no current will be induced in the coil. Hence, galvanometer will show no deflection.

*Question 14:

Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

Answer:

Two circular coils A and B are placed close to each other. When the current in coil A is changed, the magnetic field associated with it also changes. As a result, the magnetic field around coil B also changes. This change in magnetic field lines around coil B  induces an electric current in it. This is called electromagnetic induction.

*Question 15:

State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

Answer:

  1. Maxwell’s right hand thumb rule
  2. Fleming’s left hand rule
  3. Fleming’s right hand rule

*Question 16:

Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Answer:

An electric generator converts mechanical energy into electrical energy.

The principle of working of an electric generator is that when a loop is moved in a magnetic field, an electric current is induced in the coil. It generates electricity by rotating a coil in a magnetic field. The following figure shows a simple AC generator.

MNST → Rectangular coil

A and B → Brushes

C and D → Two slip rings

X → Axle, G → Galvanometer

If axle X is rotated clockwise, then the length MN moves upwards while length ST moves downwards. Since the lengths MN and ST are moving in a magnetic field, a current will be induced in both of them due to electromagnetic induction. Length MN is moving upwards and the magnetic field acts from left to right. Hence, according to Fleming’s right hand rule, the direction of induced current will be from M to N. Similarly, the direction of induced current in the length ST will be from S to T.

The direction of current in the coil is MNST. Hence, the galvanometer shows a deflection in a particular direction. After half a rotation, length MN starts moving down whereas length ST starts moving upward. The direction of the induced current in the coil gets reversed as TSNM. As the direction of current gets reversed after each half rotation, the produced current is called an alternating current (AC).

To get a unidirectional current, instead of two slip rings, two split rings are used, as shown in the following figure.

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In this arrangement, brush A always remains in contact with the length of the coil that is moving up whereas brush B always remains in contact with the length that is moving down. The split rings C and D act as a commutator.

The direction of current induced in the coil will be MNST for the first rotation and TSNM  in the second half of the rotation. Hence, a unidirectional current is produced from the generator called DC generator. The current is called AC current.

Question 17:

When does an electric short circuit occur? 

Answer:

If the resistance of an electric circuit becomes very low, then the current flowing through the circuit becomes very high. This is caused by connecting too many appliances to a single socket or connecting high power rating appliances to the light circuits. This results in a short circuit.

When the insulation of live and neutral wires undergoes wear and tear and then touches each other, the current flowing in the circuit increases abruptly. Hence, a short circuit occurs.

*Question 18:

What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Answer:

The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.

Access Answers of Science NCERT Class 10 Chapter 13 – Magnetic Effects of Electric Current

In text 13.1 Page:224

1. Why does a compass needle get deflected when brought near a bar magnet?

Solution:

The compass needle is a small magnet. When the compass needle is brought close to a bar magnet, the magnetic field lines of the compass needle interact with the magnetic field lines of bar magnet, which causes the compass needle to deflect.

In text 13.2.2 Page:228

1. Draw magnetic field lines around a bar magnet.

Solution:

Magnetic field lines of a bar magnet emerge from the North Pole and terminate at the South Pole as shown in the figure below.

NCERT Solutions Class 10 Science Chapter 13 - 1

2. List the properties of magnetic field lines.

Solution:

The properties of magnetic field lines are as follows:

  • Magnetic field lines do not intersect with each other.
  • They emerge from the North Pole and terminate at the South Pole.
  • Inside the magnet, the direction of the field lines is from the South Pole to the North Pole.

3. Why don’t two magnetic field lines intersect each other?

Solution:

If two magnetic field lines intersect then at the point of intersection the compass needle shows two different directions, which is not possible, hence they do not intersect with each other.

In text 13.2.4 Page:229

1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Solution:

NCERT Solutions Class 10 Science Chapter 13 - 2

For the downward direction of the current, the direction of the magnetic field will be as if emerging from the table outside the loop and merging with the table inside the loop. Similarly, for current flowing in an upward direction, the direction of the magnetic field will be as if they are emerging from the table outside the loop and merging with the table inside the loop, as shown in the figure.

2. The magnetic field in a given region is uniform. Draw a diagram to represent it.

Solution:

NCERT Solutions Class 10 Science Chapter 13 - 3

3. Choose the correct option.

The magnetic field inside a long straight solenoid-carrying current

  1. is zero.
  2. decreases as we move towards its end.
  3. increases as we move towards its end.
  4. is the same at all points.

Solution:

d. is the same at all points

The magnetic field inside a long straight current carrying solenoid is uniform therefore it is the same at all points.

In text 13.3 Page:231

1. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

  1. Mass
  2. Speed
  3. Velocity
  4. Momentum

Solution:

(c) and (d)

When a proton enters the region of magnetic field, it experiences magnetic force. Due to which the path of the proton becomes circular. As a result, the velocity and the momentum change.

2. In Activity 13.7, how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; and (iii) length of the rod AB is increased?

Solution:

A current carrying conductor when placed in a magnetic field experiences force. The magnitude of this force will increase with the increase in the amount of current, length of conductor and the strength of the magnetic field. Hence, the strength of the magnetic force exerted on the rod AB and its displacement will increase if

  1. The current in rod AB is increased
  2. Stronger horse shoe magnet is used
  3. When the length of the rod AB increases

3. A positively-charged particle (alpha-particle) projected towards the west is deflected towards north by a magnetic field. The direction of magnetic field is

  1. towards south
  2. towards east
  3. downward
  4. upward

Solution:

The direction of the magnetic field can be determined using the Fleming’s Left hand rule. According to the rule, if we arrange our thumb, forefinger and the middle finger of the left hand right perpendicular to each other, then the thumb points towards the direction of the magnetic force, the middle finger the direction of current and the forefinger the direction of magnetic field. Since the direction of positively charged particle is towards west, the direction of the current will also be towards the west. The direction of the magnetic force is towards the north, hence the direction of magnetic field will be upward according to Fleming’s Left hand rule.

In text 13.4 Page:233

1. State Fleming’s left-hand rule.

Solution:

Fleming’s Left hand rule states that if we arrange our thumb, forefinger and middle finger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the forefinger points towards the direction of magnetic field and the middle finger points towards the direction of current.

2. What is the principle of an electric motor?

Solution:

The working principle of electric motor is based on the magnetic effect of current. A current carrying conductor when placed in a magnetic field experiences force and rotates. The direction of the rotation of the conductor can be determined by Fleming’s Left hand rule.

3. What is the role of split ring in an electric motor?

Solution:

Split ring plays the role of commutator in an electric motor. The commutator reverses the direction of the current flowing through the coil after each half rotation of the coil. Due to this reversal of current, the coil continues to rotate in the same direction.

In text 13.5 Page:236

1. Explain different ways to induce current in a coil.

Solution:

Following are the different ways to induce current in a coil:

  • If the coil is moved rapidly between the two poles of horse shoe magnet, electric current is induced in the coil.
  • When a magnet is moved relative to the coil, an electric current is induced in the coil.

In text 13.6 Page:237

1. State the principle of an electric generator.

Solution:

Electric generator works on the principle of electromagnetic induction. In a generator, electricity is generated by rotating a coil in the magnetic field.

2. Name some sources of direct current.

Solution:

DC generator and cell are some sources of direct current.

3. Which sources produce alternating current?

Solution:

Power plants and AC generators are some of the sources that produce alternating current.

4. Choose the correct option.

A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

  1. two revolutions
  2. one revolution
  3. half revolution
  4. one-fourth revolution

Solution:

c. half revolution

When a rectangular coil is rotated in magnetic field, the direction of the induced current changes once in half revolution. As a result, the direction of the current in the coil remains the same.

In text 13.7 Page:238

1. Name two safety measures commonly used in electric circuits and appliances.

Solution:

The safety measured commonly used in electric circuits are as follows:

  1. Fuse

Each circuit should be connected to a fuse because a fuse prevents the flow of excessive current through the circuit. When the current in the circuit exceeds the maximum limit of the fuse element, the fuse melts to stop the flow of current protecting the appliance connected to circuit.

  1. Earthing

Earthing protects the user from electric shocks. Any leakage of current in an appliance is transferred to the ground by earthing and the people using the appliance is prevented from getting electrocuted.

2. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.

Solution:

The current drawn by the electric oven can be calculated using the formula

P = V × I

I = P/V

Substituting the values, we get

I = 2000 W/220 V = 9.09 A

The current drawn by the electric oven is 9.09 A which exceeds the safe limit of the circuit. This causes the fuse to melt and break the circuit.

3What precaution should be taken to avoid the overloading of domestic electric circuits?

Solution:

A few of the precautions to be taken to avoid the overloading of domestic electric circuits are as follows:

  • Connecting too many devices to a single socket should be avoided
  • Using too many appliances at the same time should be avoided
  • Faulty appliances should not be connected to the circuit

Exercises Page:240

1. Which of the following correctly describes the magnetic field near a long straight wire?

  1. The field consists of straight lines perpendicular to the wire.
  2. The field consists of straight lines parallel to the wire.
  3. The field consists of radial lines originating from the wire.
  4. The field consists of concentric circles centered on the wire.

Solution:

d. The field consists of concentric circles centered on the wire.

The magnetic field near a long straight wire are concentric circles. Their centers lie on the wire.

2. The phenomenon of electromagnetic induction is

  1. the process of charging a body.
  2. the process of generating magnetic field due to a current passing through a coil.
  3. producing induced current in a coil due to relative motion between a magnet and the coil.
  4. the process of rotating a coil of an electric motor.

Solution:

c. producing induced current in a coil due to relative motion between a magnet and the coil.

The phenomenon of inducing current in a coil due to the relative motion between the coil and the magnet

Is known as electromagnetic induction.

3. The device used for producing electric current is called a

  1. generator
  2. galvanometer
  3. ammeter
  4. motor

Solution:

a. generator

The device used for producing electric current is known as generator. Generator converts mechanical energy to electric energy.

4. The essential difference between an AC generator and a DC generator is that

  1. AC generator has an electromagnet while a DC generator has permanent magnet.
  2. DC generator will generate a higher voltage.
  3. AC generator will generate a higher voltage.
  4. AC generator has slip rings while the DC generator has a commutator.

Solution:

d. AC generator has slip rings while the DC generator has a commutator.

AC generators have two rings known as the slip rings while DC generators have two half rings known as the commutator. This is main difference between AC generator and DC generator.

5. At the time of short circuit, the current in the circuit

  1. reduces substantially.
  2. does not change.
  3. increases heavily.
  4. vary continuously.

Solution:

c. increases heavily

When two naked wires in the circuit come in contact with each other, the amount of current flowing in the circuit increase abruptly resulting in short circuit.

6. State whether the following statements are true or false.

  1. An electric motor converts mechanical energy into electrical energy.
  2. An electric generator works on the principle of electromagnetic induction.
  3. The field at the center of a long circular coil carrying current will be parallel straight lines.
  4. A wire with a green insulation is usually the live wire of an electric supply.

Solution:

a. False

An electric motor converts electrical energy into mechanical energy.

b. True

An electric generator is a device that generates electricity by rotating a coil in a magnetic field.

c. True

A long circular coil is a solenoid. The magnetic field lines inside a solenoid are parallel straight lines.

d. False

Live wires have red insulation cover while the earth wire has green insulation.

7. List two methods of producing magnetic fields.

Solution:

Following are the methods of producing magnetic fields:

  • By using a permanent magnet we can produce magnetic field and it can be visualized by spreading iron fillings on a white paper and keeping a magnet beneath the paper.
  • A current carrying straight conductor produces magnetic field.
  • Different types of conductors such as solenoid and circular loop can be used to see the presence of magnetic field.

8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain.

Solution:

A solenoid is a long coil of circular loops of insulated copper wire. The magnetic field produced around the solenoid when the current is passed through it is similar to the magnetic field produced around the bar magnet when current is passed through it. The figure shown below shows the arrangement of magnetic fields produced around the solenoid when current is passed through it.

NCERT Solutions Class 10 Science Chapter 13 - 4

When the north pole of the bar magnet is brought close to the end connected to the negative terminal of the battery, the solenoid repels the battery. As like poles repel each other, we can infer that the end connected to the negative terminal behaves as a north pole while the end connected to the positive terminal behaves as a south pole.

9. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

Solution:

When the direction of the current is perpendicular to the direction of the magnetic field is when the force experienced is the largest.

10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

Solution:

The direction of the magnetic field can be determined using the Fleming’s Left hand rule. The direction of the magnetic field will be perpendicular to the direction of current and the direction of deflection, i.e., either upward or downward. The direction of the current is from the front wall to the back wall because negatively charged electrons move from the back wall to the front wall. The directed of the magnetic force is rightward. Hence, using Fleming’s left hand rule it can be concluded that the direction of the magnetic field inside the chamber is downward.

11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

Solution:

An electric motor is a device that converts electrical energy to mechanical energy. It works on the principle of magnetic effect of current. The figure listed below shows a simple electric motor.

NCERT Solutions Class 10 Science Chapter 13 - 5

When current is made to flow through the coil MNST by closing the switch, the coil starts to rotate in the anticlockwise direction. This is due to the downward force acting on the length MN and simultaneously an upward force acting along the length ST. As a result of which the coil rotates in the anticlockwise direction. Current in the length MN flows from M to N and the magnetic fields act from left to right normal to the length MN. According to Fleming’s Left Hand rule, a downward force acts along the length MN. Similarly, the current along the length ST flows from S to T and the magnetic field acts from left to right. Therefore, an upward force acts along the length ST. These two forces together cause the coil to rotate anti-clockwise. After half a rotation, the position of MN and ST interchange. The half ring C come in contact with brush B and the half ring D comes in contact with rush C. Hence the direction of current in the coil MNST gets reversed.

12. Name some devices in which electric motors are used.

Solution:

A few devices in which electric motors are used are:

  • Electric fans
  • Water pumps
  • Mixers
  • Washing machines

13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

Solution:

(i) When a bar magnet is pushed into the coil, current is induced in the coil momentarily as a result the galvanometer deflects in a particular direction momentarily.

(ii) When the bar magnet is withdrawn from inside the coil, current is induced momentarily but in the opposite direction and the galvanometer deflects in the opposite direction momentarily.

(iii) When the bar magnet is held stationary inside the coil, no current will be induced as a result there will be no deflection in the galvanometer.

14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

Solution:

When the current in coil A changes, the magnetic field associated with it also changes. As a result the magnetic field around coil B undergoes change. The change in the magnetic field of coil B induces current in it.

15. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

Solution:

(i) The rule used to determine the direction of the magnetic field produced around a straight conductor-carrying current is the Maxwell’s right hand thumb rule.

(ii) The rule used to determine the force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it is the Fleming’s left hand rule.

(iii) The rule used to determine the current induced in a coil due to its rotation in a magnetic field is the Fleming’s right-hand rule.

16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Solution:

The electric generator coverts the mechanical energy into the electrical energy. The working principle of the electric generator is the electromagnetic induction. It generates electricity by rotating a coil in the magnetic field. The figure below shows the construction of a simple AC generator.

NCERT Solutions Class 10 Science Chapter 13 - 6

In the diagram,

A and B are brushes,

C and D are slip rings

X is the axle

G is the galvanometer

When the axle X is rotated clockwise, MN moves upwards while ST moves downward. The movement of MN and ST in the magnetic field results in the production of electric current due to electromagnetic induction. MN moves upwards and the magnetic fields act from left to right. Therefore, according to Fleming’s right hand rule, the direction of the induced current will be from M to N along the length MN. Similarly, the direction of the induced current will be from S to T along the length ST. The direction of the current in the coil is MNST. Hence, galvanometer shows a deflection in a particular direction.

After half a rotation, length MN starts moving downwards while the length ST starts moving upwards. Now, the direction of the induced current reverses to TSNM. Since the direction of the induced current reverses every half rotation, the current induced is known as alternating current.

Function of Brushes

Brushes are kept pressed on to two slip rings separately. Outer ends of brushes are connected to the galvanometer. Thus, brushes help in transferring current from coil to the external circuit.

  1. When does an electric short circuit occur?

Solution:

Listed below are two instances of when a short-circuit can occur:

1) When too many appliances are connected to a single socket or when high power rating appliances are connected to a light circuit, the resistance of the circuit becomes low as a result the current flowing through the circuit becomes very high. This condition results in a short-circuit.

2) When live wires whose insulation have worn off come in contact with each other, the current flowing in the circuit increases abruptly which results in a short circuit.

18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Solution:

The metallic body of electric appliances is earthed by means of earth wire. Any leakage of electric wire is transferred to the ground by means of earth wire. This prevents the user of the electric appliance from getting electric shocks. This is the reason why it is important for the metallic appliances to be earthed.


NCERT Solutions for Class 10 Science Chapter 13 – Magnetic Effects of Electric Current

As per the updated marking scheme, NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current is one of the important topics and the expected weightage is 10 marks. In this chapter, students learn more in detail about Electric Current, Magnetic fields, magnetic fields lines, compass, electromagnetic induction, Effects of Electric Current and so on. Oersted law and his Experiment is the most important 5 mark question, which has been the most frequently asked in the previous year papers.

List of Exercises

13.1 Magnetic Field and Field Lines

13.2 Magnetic Field due to a Current-Carrying Conductor

13.3 Force on a Current – carrying Conductor in a Magnetic Field

13.4 Electric Motor

13.5 Electromagnetic Induction

13.6 Electric Generator

Magnetic Effects of Electric Current is also known as the electromagnetic effect. It is the branch of physics which mainly deals with the study of the electromagnetic force, electrically charged particles, electric fields and magnetic fields. In this topic, students can learn more interesting concepts related to the Magnetic fields and the Electric Current, along with a few interesting experiments. Other interesting topics explained in this chapter include:

  • Properties of the magnet – 2 Questions (1 short, 1 MCQ)
  • How does magnetic effect works -1 Question (1 MCQ)
  • Clock Face Rule-1 Question (1 short)
  • Fleming’s left-hand rule-1 Question (1 long)
  • Maxwell’s Right Hand Thumb Rule and its Application -1 Question (1 long)

Key Features of NCERT Solutions for Class 10 Science Chapter 13 – Magnetic Effects of Electric Current:

  • Provides completely solved solutions to all the questions present in the respective NCERT textbooks.
  • The language used in these NCERT Solutions is easy and simple to understand by the students.
  • These solutions are prepared by our subject experts after extensive research on every topic, in order to provide appropriate and genuine information to the students.
  • These solutions will be useful for Olympiads, CBSE board exams and other competitive exams.
  • Detailed answers are provided to all the questions to help students in their preparations.

Frequently Asked Questions on NCERT Solutions for Class 10 Science Chapter 13

How to determine the direction of magnetic field in the Chapter 13 of NCERT Solutions for Class 10 Science?

The direction of the magnetic field can be determined using many processes. The movement of the compass needle within the magnetic field indicates the direction of the magnetic field. There are few other rules which help us to find the direction of the magnetic field. Right-hand thumb rule is one among them. It states that if we place the current carrying wire in our right hand, the thumb indicates the direction of current flow and the fingers around the wire indicate the direction of the magnetic field lines.


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NCERT Solutions Class 10 Science Chapters

  • Chapter 1 Chemical Reaction and equation
  • Chapter 2 Acid, Base and Salts
  • Chapter 3 Metals & Non-Metals
  • Chapter 4 Carbon and its Compounds
  • Chapter 5 Periodic Classification of Elements
  • Chapter 6 Life Processes
  • Chapter 7 Control and Coordination
  • Chapter 8 How do Organisms Reproduce
  • Chapter 9 Heridity
  • Chapter 10 Light, Reflection & Refraction
  • Chapter 11 Human Eye
  • Chapter 12 Electricity
  • Chapter 13 Magnetic effects of electric current
  • Chapter 14 Sources of Energy
  • Chapter 15 Environment

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