NCERT Solutions for Class 10 Science Chapter 12 Exercise

Answer: The magnetic field of the magnet exerts force on both the poles of the compass needle. These two forces form a couple which deflects the compass needle.

Answer: Magnetic field lines around a bar magnet are shown in below image —

Answer: Properties of magnetic lines of force –

1. The magnetic field lines originate from the north pole of a magnet and end at its south pole.
2. The magnetic field lines become closer to each other near the poles of a magnet but they are widely separated at other places.
3. Two magnetic field lines do not intersect one another.

Answer: If two magnetic field lines of force intersect each other then at the point of intersection, the compass needle would show two different directions which is not possible.

Answer: You can see in the image below that each section of wire produces its concentric set of lines of force.

Now, by applying the right hand thumb rule, we find that all the sections produce magnetic field downwards at all points inside the loop while at the outside points, the field is directed upwards. Therefore, the magnetic field acts normally into the plane of the paper at the points inside the loop and normally out of the plane of paper at points outside the loop.

Answer: Uniform magnetic field could be represented by drawing parallel and equidistant straight lines, all pointing in the same direction –

Answer: (d) is the same at all points.

Answer: (c) velocity, and (d) momentum

Answer: (i) When the current in the rod AB is increased, force exerted on the conductor increases, so the displacement of the rod increases.

(ii) When a stronger horse-shoe magnet is used, the magnitude of the magnetic field increases. This increases the force exerted on the rod and the displacement of the rod.

(iii) When the length of the rod AB is increased, force exerted on the conductor increases, so the displacement of the rod increases.

Answer: (d) upward

Answer: Two safety measures are –
(i) Earthing
(ii) Electric fuse

Answer: The current drawn by the electric oven,
I = P/V
Substituting the values,
I = 2000/220 = 9.09 A

The current drawn by the electric oven is 9.09 A which exceeds the safe limit of the circuit. Due to excessive current, the fuse wire will blow and the circuit will break.

Answer: Precautions to avoid the overloading of domestic electric circuits –
(i) Too many appliances should not be connected to a single socket.
(ii) Wires used in the circuit must be coated with good insulating materials like PVC.
(iii) Fuse should be connected in the circuit.

Answer: (d) The field consists of concentric circles centered on the wire.

Answer: (c) increases heavily.

(a) The field at the centre of a long circular coil carrying current will be parallel straight lines.

Answer: True

(b) A wire with a green insulation is usually the live wire of an electric supply.

Answer: False

Answer: Two methods of producing magnetic fields are –
(i) The permanent magnet produces a magnetic field around it.
(ii) Passing current through a conductor also produces the magnetic field.

Answer: The force experienced by a current-carrying conductor is largest when the direction of the current is perpendicular to the direction of the magnetic field.

Answer: The direction of the magnetic field is vertically downwards. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from the 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.

Answer: (i) Maxwell’s right hand thumb rule.
(ii) Fleming’s left hand rule.
(iii) Fleming’s right-hand rule.

Answer: 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.

Answer: It is necessary to earth metallic appliances because it ensures that if there is any current leakage in the metallic cover, the potential of the appliance becomes equal to that of the earth. The potential of the earth is zero. As a result, the person handling the appliance will not get an electric shock.