Question

a student is measuring the effects of an electric circuit on a compass, and he is testing to see if increasing the current will cause the compass needle to change its direction faster. he does one trial using a 9-volt battery and another trial using a 1.5-volt battery. he takes accurate data. based on good experimental design, what would improve his experiment?
he should use only one battery but do several trials, using different circuit designs to ensure he has appropriate test groups.
he should repeat the test with three additional batteries of varying voltages to demonstrate the reproducibility of results.
he should add a nonworking compass to act as a control.
he should use batteries of the same voltage but from different manufacturers to show he has used different variables.

Explanation:

To improve the experiment, we need to consider experimental design principles like reproducibility and testing the relationship between current (related to voltage) and the compass response.

• The first option introduces different circuit designs, which adds a new variable (circuit design) instead of focusing on voltage, so it's not good.
• The second option: repeating the test with three additional batteries of varying voltages will give more data points across a range of voltages, helping to demonstrate if the relationship (between voltage/current and compass direction change speed) is consistent, thus improving reproducibility and the validity of the experiment.
• The third option: a nonworking compass as a control isn't relevant here since the experiment is about the effect of the electric circuit (current) on a working compass's direction change, so this control doesn't address the variable of interest.
• The fourth option: using batteries of the same voltage from different manufacturers introduces a variable (manufacturer) that's not related to the research question (effect of current/voltage on compass), so it's not helpful.

Answer:

He should repeat the test with three additional batteries of varying voltages to demonstrate the reproducibility of results.