Question

4.2.2 quiz: electromagnetism
question 5 of 10
why are electromagnets more useful than permanent magnets in many modern technologies?
a. a power supply is not necessary to use an electromagnet.
b. permanent magnets with the same strength are heavier.
c. electromagnets can be turned on and off by controlling the current.
d. the strength of the magnetic field is more consistent in permanent magnets.

Explanation:

Electromagnets' key advantage is their controllability via current. Option A is wrong as electromagnets need power. Option B about weight isn't a main tech - use reason. Option D is incorrect as electromagnets can vary strength. Option C highlights the on - off and strength - adjustable (by current) feature which is crucial in modern tech.

Answer:

C. Electromagnets can be turned on and off by controlling the current.