Question

4.3.2 test (cst): electromagnets
question 11 of 20
larry plans to connect the opposite ends of a coiled wire to a 10 w lightbulb to make the bulb light up. what must he also do to induce an electric current in the wire?
a. move the lightbulb so that several of the coils in the wire wrap around the bulb.
b. move a small magnet back and forth within a section of the coiled wire.
c. move the lightbulb and the coiled wire around a magnet until the bulb lights up.
d. move a small electromagnet around the lightbulb continuously until the bulb lights up.

Explanation:

According to Faraday's law of electromagnetic induction, an electric current is induced in a coil when there is a change in magnetic flux through the coil. Moving a magnet back and forth within a section of the coiled wire changes the magnetic flux through the coil, which induces an electric current. Option A only changes the position of the light - bulb with respect to the coil but does not change the magnetic flux. Option C moves the whole circuit (coil + bulb) around a magnet, but if the relative motion between the coil and the magnet is not such that the magnetic flux through the coil changes (e.g., moving them together in a uniform magnetic field region), no current is induced. Option D moves the electromagnet around the light - bulb, but the key is the relative motion between the magnet and the coil (not the light - bulb).

Answer:

B. Move a small magnet back and forth within a section of the coiled wire.