Chapter 12: Magnetic Effects of Electric current    

Multiple Choose Question and Answer :

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

(a) The field consists of straight lines perpendicular to the wire.

(b) The field consists of straight lines parallel to the wire.

(c) The field consists of radial lines originating from the wire.

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

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

[ Around a long straight current-carrying wire, the magnetic field lines form concentric circular paths centred on the wire.]

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

(a) reduces substantially.

(b) does not change.

(c) increases heavily.

(d) vary continuously.

Answer :  (c) increases heavily. 

[ During a short circuit, the resistance becomes very low, so a large amount of current flows through the circuit suddenly. ]

Question: Choose the correct option.

The magnetic field inside a long straight solenoid-carrying current

(a) is zero.

(b) decreases as we move towards its end.

(c) increases as we move towards its end.

(d) is the same at all points.

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

[ Inside a long straight solenoid carrying current, the magnetic field is uniform, and its strength is the same at all points along the axis of the solenoid. This is one of the unique characteristics of a well-designed solenoid.]

Short Question and Answer :

Question: When is the force experienced by a current–carrying conductor placed in a magnetic field largest ? [1M]

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

Question: Why does a compass needle get deflected when brought near a bar magnet? [2M]

Answer:  A compass needle gets deflected when brought near a bar magnet due to the magnetic field produced by the magnet. The compass needle aligns itself with the magnetic field lines, indicating the presence and direction of the magnetic field.

Question: A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it? [2M]

Answer : At a point directly below the horizontal power line, the direction of the magnetic field is vertically upward. At a point directly above the horizontal power line, the direction of the magnetic field is vertically downward.

Question: 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. [2M]

Answer: Here,  and

We have,

The current required by the oven (9.09 A) exceeds the circuit's current rating (5 A). As a result, the circuit will likely be overloaded, causing the fuse to blow or a circuit breaker to trip, cutting off the electricity supply to prevent damage or fire.

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

Answer: The function of an earth wire is to provide a safe path for leakage current to flow into the ground, preventing electric shocks.

It is necessary to earth metallic appliances because if the live wire accidentally touches the metallic body, the current flows through the earth wire instead of the user, protecting against potential electric shocks and ensuring safety.

Question:  List the properties of magnetic lines of force.

Answer: The properties of magnetic lines of force are:

(i)  They always form closed loops, emerging from the north pole and entering the south pole.

(ii)  They never intersect each other.

(iii) The density of lines indicates the strength of the magnetic field.

(iv)  They repel each other in a uniform field.

(v) They are directed from the north to the south pole outside the magnet.

Question: 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.[3M]

Answer: A solenoid behaves like a magnet due to the magnetic field generated by the current flowing through its coil. The magnetic field lines produced by the solenoid resemble those of a bar magnet. The north and south poles of a solenoid can be determined using a bar magnet. When one end of a bar magnet is brought close to the solenoid, it will either attract or repel the end of the bar magnet, indicating the opposite pole of the solenoid.

Long Question and Answer :

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