Question

Why must the test charge be vanishingly small when measuring an electric field?

Options

• So that it does not modify the field of the source charge

• So that it experiences no force at all

• So that it acquires the same sign as the source charge

• So that it moves faster in the field

Answer 1

The test charge must be vanishingly small so that it does not modify the field of the source charge. If the test charge were large, its own field would disturb the original field distribution being measured.