Question

Charlotte built a simple electromagnet, shown below.


She found that the electromagnet picked up the entire pile of paper clips the instant she turned it on. Which of the following might allow Charlotte's electromagnet to pick up a single paper clip at a time?

increasing the number of batteries supplying voltage to the electromagnet
increasing the number of loops in the electromagnet's coil
increasing the distance between the electromagnet and the paper clips
removing the iron nail from the core of the electromagnet

Answer 1

Answers: increasing the distance between the electromagnet and the paper clips, and removing the iron nail from the core.

Explanation: To pick up only one clip you need a weaker field. Increasing distance reduces field strength at the clips. Removing the iron (ferromagnetic) core greatly reduces the magnet's strength. By contrast, adding batteries or more coil turns increases current or N·I and so would make the magnet stronger (not weaker).