Magnetic Force

Magnetic Force

Multiple Choice

Suki was investigating magnetism with two bar magnets. She finds that her magnets stick to some surfaces like the refrigerator door, the sink, and the window frame. The magnets did not stick to the window glass, the door, or the wall.

What types of material attract a magnet?

• materials containing any type of metal

• materials that are shiny

• materials that contain iron

• materials that contain another magnet

​Explanation

​The correct answer is “materials that contain iron.” While magnets are attracted to some types of metal (such as iron, nickel, and cobalt), not all metals are attractive to magnets (such as copper, zinc, and aluminum). An object’s shine is not related to whether it will attract a magnet. Materials that contain a magnet may either be attractive or repulsive, depending on which poles come in contact with each other.

Multiple Select

Suki was investigating magnetism with two bar magnets. She finds that her magnets stick to some surfaces like the refrigerator door, the sink, and the window frame. The magnets did not stick to the window glass, the door, or the wall.Next, she decides to investigate their magnetic force. What tests could she perform to determine which magnet has a stronger magnetic force? Choose the two that apply.

• Put both magnets on a refrigerator door, and test which requires more force to pull it off the door.

• Put them next to each other, and test how much force is required to separate the two magnets.

• Pour iron filings onto both magnets while they are close together and see which magnet collects the largest pile of filings.

• Pour iron filings onto both magnets while they are apart and see which filings arrange into lines that are closer together.

​Explanation

​The correct answers are “Put both magnets on a refrigerator door, and test which requires more force to pull off the door” and “Pour iron filings onto both magnets while apart and see which filings arrange into lines that are closer together.” Putting the magnets together and trying to pull them apart does not test the individual strength of each magnet, so it cannot be used as a test to determine which has a stronger magnetic force. Similarly, if the magnets are together, the iron filings will follow the magnetic lines of the combined magnetic force of both magnets instead of being attracted to each magnet individually.

Multiple Choice

Naji was using his computer to model the strength of the magnetic field around a bar magnet. He knows that certain parts of the magnetic field are stronger than others. Where are the strongest and weakest parts of the magnetic field shown in the diagram?

• strongest: A, weakest: B

• strongest: A, weakest: D

• strongest: C, weakest: A

• strongest: C, weakest: B

​Explanation

​The correct answer is “strongest: C, weakest: D.” Although A is centered on the pole, it is further away from the magnet than point C and is therefore weaker. Point B and D are both weaker than either point A or C. Point B is further away from the magnet than D and therefore is weaker.

Multiple Choice

Justin was creating a chart comparing the potential energy between charged particles and the potential energy of magnets. Which of the following is true?

• The potential energy between both like charges and like poles increases as they move closer together.

• The potential energy increases between like charges and decreases between like poles as they move closer together.

• The potential energy between both like charges and like poles decreases as they move closer together.

• The potential energy decreases between like charges and increases between like poles as they move closer together.

​Explanation

​The correct answer is “The potential energy between both like charges and like poles increases as they move closer together.” For both electric and magnetic potential energy, like charges or poles moving closer results in increased potential energy. Moving like charges and poles farther apart results in decreased potential energy, based on their naturally repelling properties. For both electric and magnetic potential energy, opposite charges or poles moving closer results in decreased potential energy. Moving opposite charges farther apart results in increased potential energy, based on their naturally attractive properties.