Magnetic Forces and Distance

What is the area around a magnet where magnetic forces can be felt called?

• Magnetic field

• Magnetic pole

• Electric field

• Gravitational field

Answer explanation

The area around a magnet where magnetic forces can be felt is called the magnetic field. This is where magnetic influence extends, affecting materials like iron and steel.

Iron filings are placed near a coil of copper wire. Which of the following will most likely cause the iron filings to move?

• Heating the copper wire

• Sending an electric current through the copper wire

• Making smaller turns in the copper wire

• Increasing the number of turns in the copper wire

Answer explanation

A current in the wire creates a magnetic field, which can move the iron filings. Heating the wire does not produce a magnetic effect, and making smaller turns affects field strength but does not necessarily induce motion.

Explain how distance affects the strength of the magnetic forces between two objects based on the image shown and how this is related to electric force and distance.

• The electrical force between the magnet and paper clips is only in effect when they are touching.

• The electrical force between the magnet and paper clips increases as the distance between them increases.

• The electrical force between the magnet and paper clips is not affected by distance.

• The electrical force between the magnet and paper clips increases as the distance between them decreases.

Answer explanation

Magnetic and electric forces follow an inverse-square law, meaning that as distance decreases, the force increases.

Three unmarked bar magnets are brought close together at the ends, two at a time. Magnet A and Magnet B repel each other. Magnet A and Magnet C repel each other. Magnet B and Magnet C repel each other. Which of the following statements CAN be determined from these results alone?

• A. Bars A and B have like poles near one another.

• B. Rods A and C have like poles near one another.

• C. Rods B and C have like poles near one another.

• D. All of the above

Answer explanation

Repulsion occurs between like poles. Since each pair repels, it confirms that all three magnets have the same pole facing one another.

Identify in the diagram where the magnetic field would be the greatest. Choose the THREE best answers.

• 3

• 2

• 4

• 5

• 1

Answer explanation

The magnetic field is strongest near the poles of the magnet, where field lines are most concentrated.

You loaned your favorite magnet to a neighbor to find a lost metal treasure in their backyard. The friend drops and breaks your magnet. What is the best explanation of what will happen to the magnetic force in your broken pieces?

• The pieces will either be only the North pole or South pole and become monopole magnets.

• The pieces will be smaller magnets having both a North or South pole.

• The magnet will become electrified and can be used as an electromagnet.

• The magnet will no longer be magnetic because the electrons have lost their magnetic ability.

Answer explanation

Breaking a magnet results in smaller magnets, each with its own North and South poles, rather than isolated monopoles.

The force between two magnets is inversely proportional to the square of the distance between them. If the distance doubles, how does the force change?

• The force stays the same.

• The force is halved.

• The force is quartered.

• The force doubles.

Answer explanation

Since the force follows an inverse-square law, doubling the distance results in the force being reduced to one-fourth of its original value.

If the distance between two magnets is halved, what happens to the magnetic force between them?

• The force is halved.

• The force is quadrupled.

• The force is doubled.

• The force remains unchanged.

Answer explanation

When the distance is halved, the force increases by four times due to the inverse-square relationship.

Which of the following is an example of simple harmonic motion (SHM)?

• A. A car accelerating on a straight road

• B. A child on a swing moving back and forth

• C. A person walking across a room

• D. A person throwing a ball in the air

Answer explanation

Simple harmonic motion (SHM) involves periodic oscillation around an equilibrium position, which describes a swinging motion.

What is the period of oscillation for a mass-spring system dependent on?

• The amplitude of oscillation

• The frequency of the wave

• The mass of the object and the spring constant

• The velocity of the mass

Answer explanation

The period of a mass-spring system depends on these factors according to the equation T=2πm/kT = 2\pi \sqrt{m/k}T=2πm/k​.