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# Class 10 NCERT Solutions Physics Chapter 12 - Magnetic Effects of Current

## Magnetic Effects of Current Exercise 196

### Solution 1

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 a bar magnet.

Concept Insight: Magnetic fields interact with each other. Interaction of magnetic field of earth and that of the compass needle is used to find directions.

## Magnetic Effects of Current Exercise 200

### Solution 1

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.

Concept Insight:-  Note that magnetic field lines never intersect each other.

### Solution 2

The properties of magnetic lines of force are as follows.

1. Outside a magnet, magnetic field lines are directed from North pole to South pole.

2. The direction of field lines inside the magnet is from the South pole to the North pole.

3. Magnetic lines do not intersect with each other.

4. Magnetic lines of force are crowded near the poles of a magnet but they are widely separated at other places.

### Solution 3

If two field lines of a magnet intersect, then at the point of intersection, there would be two directions of magnetic field. This is not possible. Hence, two field lines do not intersect each other.

Concept Insight:-  Note that magnetic field lines never intersect each other.

## Magnetic Effects of Current Exercise 201

### Solution 1

Applying right hand thumb rule to the loop:

For right side of 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 left side of 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.

### Solution 2

Concept Insight: The uniform magnetic field is represented by parallel and equidistant magnetic field lines.

## Magnetic Effects of Current Exercise 202

### Solution 3

(d) is the same at all points

Concept Insight:-
The magnetic field inside a long, straight, current-carrying solenoid is uniform. It is the same at all points inside the solenoid.

## Magnetic Effects of Current Exercise 203

### Solution 1

(c) velocity and (d) momentum

Concept Insight:-

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. So, its velocity and hence momentum change.

## Magnetic Effects of Current Exercise 204

### Solution 2

Concept Insight:-A force is experienced by a current-carrying conductor placed in a magnetic field. The magnitude of force increases with the increase in 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

(i) current in rod AB is increased

(ii) a stronger horse-shoe magnet is used

(iii) length of rod AB is increased

### Solution 3

(d) upward

The direction of the magnetic field can be determined by the Fleming's left hand rule.

Concept Insight:-According to Fleming's left hand rule, if we arrange the thumb, the central finger, and the forefinger of the left hand at right angles to each other and if the forefinger points in the direction of magnetic field, the central finger points in the direction of current, then the thumb points in the direction of motion of the conductor.

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.

## Magnetic Effects of Current Exercise 205

### Solution 1

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

(i) 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.

(ii) 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.

Concept Insight:- Safety measures like fuse and earthing are very necessary in case of electrical circuits and appliances as an electric shock may prove to be deadly.

### Solution 2

Concept Insight:-

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

P = VI

where,
Current = I
Power of the oven, P = 2 kW = 2000 W
Voltage supplied, V = 220 V

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.

### Solution 3

The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
(a) Too many appliances should not be connected to a single socket.
(b) Too many appliances should not be used at the same time.
(c) Faulty appliances should not be connected in the circuit.
(d) Fuse should be connected in the circuit.

Concept Insight:- Safety measures like fuse and earthing are very necessary in case of electrical circuits and appliances as an electric shock may prove to be deadly.

## Magnetic Effects of Current Exercise Ex. 207

### Solution 1

(d) The field consists of concentric circles centred on the wire.

Concept Insight:- The magnetic field lines, produced around a straight current-carrying conductor, are concentric circles. Their centres lie on the wire.

### Solution 5

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.

### Solution 6

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.

### Solution 2

(c) increases heavily

Concept Insight:- 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.

### Solution 3

(a) True

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

(b) False

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

### Solution 4

Two methods of producing magnetic field are as follows:

(a) By using current-carrying conductors

(b) By using permanent magnets

(c) By electromagnets

### Solution 7

(i) Right hand thumb rule
(ii) Fleming's left hand rule
(iii) Fleming's right hand rule

### Solution 8

An electric short circuit occurs when the live wire and the neutral wire come in direct contact. This happens when the plastic insulation of live wire and neutral wire gets torn or when there is a fault in the electrical appliance.

### Solution 9

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.