Eighth Grade · Science · week 25

Build: electromagnet strength test

Describe an investigation building an electromagnet and testing which variables change its strength, using a controlled-experiment design.

An electromagnet is a magnet created by electric current: wrap insulated wire in a coil around an iron nail, connect the ends to a battery, and the nail becomes magnetic as long as current flows. This differs from a bar magnet, which stays magnetic all the time.

Two variables change an electromagnet's strength: more coil turns generally makes it stronger, and more current (from a stronger or additional battery) also makes it stronger. To test fairly, change only one variable at a time while holding everything else the same.

📋 For the teacher
Teach it (10–15 min):
  • Build a real electromagnet if materials allow -- a nail, thin insulated wire, a battery, and paper clips are all that is needed.
  • Insist on changing only one variable per trial, naming what is tested and what is held constant.
  • Record the paper-clip count for each trial like real data, comparing numbers rather than a vague impression.
Talk about it:
  • Why is it important to change only one variable at a time when testing the electromagnet?
  • What are the two main ways to make an electromagnet stronger?

Mastery looks like: They describe a controlled test of electromagnet strength, identifying the one changed variable and the variables held constant.

Common stumbles: Changing more than one variable between trials, making it impossible to tell which change caused the result.

Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
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