Question

Which of the following figures depict a non uniform magnetic field?
(A)
 

(B)
 

(C)
 

(D)

Answer 1

Hint: The strength of a magnetic field can be qualitatively determined by the length spacing of the magnetic field lines. A non uniform magnetic field is a magnetic field which does not have equal strength everywhere it exists.

Complete step by step solution:
In general, we say a magnetic field can be uniform or non-uniform. A uniform (sometimes called constant) magnetic field can be said to be a magnetic field whose strength is equal everywhere it exists. This is to say that it does not decay or reduce in strength with location. On the other hand, a non-uniform magnetic field is one which changes, whose strength is not equal everywhere it exists. That is to say, the strength varies with location.
Now magnetic fields are often represented graphically using what is called magnetic field lines. Now, usually these lines are drawn with arrows pointed in the direction of the magnetic field. And the strength is represented by the line density of the diagram , that is how compact or distant the lines are to each other.
Now, we need to investigate the options given to find which of them is not a uniform magnetic field. This would be the field lines in which all its lines are not equally spaced out (not equal strength everywhere)
Hence, option D is the correct answer.

Note:
For clarity, we should note that creating a uniform magnetic field is difficult, and it’s usually an idealisation. Most sources create non uniform fields because they vary in their strength depending on location. Ideally, a uniform field is to end abruptly at its maximum reach, but that often isn’t the case, as most fields gradually diminish.