Question

Directions: Read the passage about the factors that affect the magnetism of electromagnets.

An electromagnet consists of an insulated copper wire wound around an iron core and connected to a source of electricity. The magnetism of electromagnets disappears when the electricity is turned off. A student performs two experiments to study the factors that affect the magnetism produced by an electromagnet.

Experiment 1
He prepares an electromagnet by wrapping ten coils of a wire around an iron nail. The wire is then connected to a 4.5-volt battery. Next, the electromagnet is placed close to evenly spread iron paper clip





He records the number of paper clips that are attracted to the magnet in a table, repeating the activity with different numbers of coils around the nail.

Number of coils Number of paper clips attracted to the magnet
10 6
15 11
20 17
25 23


Experiment 2
In his second experiment, he repeats the same procedure he used in Experiment 1, except that this time he keeps the number of coils the same but changes the battery voltage. He records the number of paper clips attracted each time in a second table.

Battery Voltage (V) Number of paper clips attracted to the magnet
3.0 3
4.5 6
6.0 9
7.5 13
Which question can be answered based on the results of Experiment 2?

a
How does the strength of an electromagnet vary when the voltage of the power source changes?
b
How does the strength of an electromagnet vary when the number of paper clips changes?
c
How does the voltage of an electromagnet vary when the strength of the paper clips changes?
d
How does the voltage of an electromagnet vary when the number of coils of wire changes?
Question 2 (1 point)
Brielle tests the difference in the magnetic force of two electromagnets with different numbers of wire turns around the iron nails. She observes that the electromagnet with ten wire turns attracts more paper clips than the electromagnet with seven wire turns. What is her conclusion?

a
Magnetic force increases with a decrease in the number of wire turns around an iron nail.
b
Magnetic force decreases with an increase in the number of wire turns around an iron nail.
c
Magnetic force is not affected by a change in the number of wire turns around an iron nail.
d
Magnetic force increases with an increase in the number of wire turns around an iron nail.
Question 3 (3 points)
A student built a simple electromagnet with copper wire, an iron bolt, and a 1.5-volt battery. The electromagnet was able to lift a paper clip from 3 centimeters away. Select three ways the student can increase the strength of his electromagnet.

a
He can replace the iron bolt with a wooden rod.
b
He can reverse the orientation of the battery.
c
He can use a longer piece of wire that wraps more times around the bolt.
d
He can use a thicker piece of copper wire.
e
He can add a switch between the battery and the iron bolt.
f
He can replace the 1.5-volt battery with a battery of higher voltage.

Answer 1

Question 1: a

Question 2: d

Question 3: c, d, f

Brief reasons:
- Exp. 2 changes battery voltage and measures attracted clips, so it answers how electromagnet strength varies with voltage (a).
- More wire turns produced a stronger magnet, so magnetic force increases with more turns (d).
- Ways to increase strength: add more turns (c), use thicker wire to allow more current (d), and use a higher-voltage battery (f). Replacing the bolt with wood or just adding a switch won't increase strength; reversing the battery only reverses polarity.