Question

4.2.2 quiz: electromagnetism
question 2 of 10
if a wire lies within a magnetic field, what must be true for the magnetic field to produce an electric current in the wire?
a. the field must not be moving.
b. the field must be moving.
c. the field must be produced by an electromagnet.
d. the field must be produced by induced magnetism.

Explanation:

Step1: Recall electromagnetic induction

Electromagnetic induction is the process of generating an electric current in a conductor (like a wire) placed in a changing magnetic field.

Step2: Analyze each option

• Option A: If the field is not moving (no change in magnetic field), there is no electromagnetic induction. So, this option is wrong.
• Option B: When the magnetic field is moving (changing), it causes a change in magnetic flux through the wire. According to Faraday's law of electromagnetic induction, a changing magnetic flux induces an electromotive force (emf) in the wire, which in turn can cause an electric current if the circuit is closed. This option is correct.
• Option C: The magnetic field can be from any source (permanent magnet or electromagnet) as long as it is changing. So, this option is wrong.
• Option D: The source of the magnetic field (whether it is due to induced magnetism or not) is not relevant. What matters is the change in the magnetic field. So, this option is wrong.

Answer:

B. The field must be moving.