Question

a group of students builds an electromagnet by turning wire around a nail, and then connecting the ends of the wire to a battery. the students can hang some number of paper clips from the nail, as shown below. the students predict that increasing the number of turns of wire around the nail will increase the strength of the electromagnet. they plan an investigation to test their prediction. what should they select as the controlled variables for their investigation? choose 2 answers: a paperclip size b number of paperclips that hang from the nail c number of turns of wire around the nail d battery voltage

Explanation:

To determine controlled variables, we identify factors that must stay constant to test the effect of the independent variable (number of wire turns) on the dependent variable (electromagnet strength, measured by paperclips held).

• Option A (paperclip size): Must be constant; different sizes would affect how many can be held, interfering with measuring strength.
• Option B (number of paperclips): This is the dependent variable (or what we measure), not a controlled variable.
• Option C (number of wire turns): This is the independent variable (the one we change), not controlled.
• Option D (battery voltage): Must be constant; voltage affects current and thus electromagnet strength, so changing it would confound the results of changing wire turns.

So the controlled variables are paperclip size and battery voltage.

Answer:

A. paperclip size, D. battery voltage