Physics
The diagrams given below show some magnetic field patterns.

Answer the following questions :
(a) Which pattern shows uniform magnetic field lines?
(b) Which pattern is for a straight current carrying wire?
(c) Which pattern is depicted by current in a loop?
Answer
(a) Pattern D
Reason — Pattern D shows uniform magnetic field lines because it contains parallel, equally spaced straight lines indicating a uniform magnetic field.
(b) Pattern A
Reason — The pattern for the magnetic field around a straight current carrying wire is concentric circles around it which is shown in pattern A. So, A shows pattern of magnetic field for a straight current carrying wire.
(c) Pattern B
Reason — In pattern B, magnetic field lines are emerging from the loop and curving which is equivalent to a circular current carrying loop. So, B shows pattern depicted by current in a loop.
Related Questions
A student draws three magnetic field lines 1, 2, 3 of a bar magnet using a compass needle. Are all the lines of force correctly drawn? Give reason for your answer.

The diagram given below shows magnetic field pattern around a bar magnet. Identify the poles A and B.

A straight wire lying in a horizontal plane carries a current from north to south. (a) What will be the direction of magnetic field at a point just underneath it? (b) Name the law used to arrive at the answer in part (a).
A wire, bent into a circle, carries current in an anticlockwise direction. What polarity does this face of the coil exhibit?