Magnetism Review

A compass will point towards a magnetic field, and can help people find their way in unfamiliar places by pointing to the North Pole of the Earth's magnetic field. A student notices that a nearby compass turns toward a wire when a current is passed through the wire. What can the student conclude based on this observation?

• Compasses do not have magnetic fields.

• Compasses produce electric currents.

• Electric current produces a magnetic field.

• Magnetic fields produce an electric field.

A pair of students were asked to see if the electric current flowing through a wire would have any effect on a magnetic compass. Which of the following is NOT a variable that would be likely to affect the results?

• The distance of the compass from the current carrying wire.

• How much current is flowing through the wire.

• The number of loops in the coil of wire.

• The size of the compass.

Two students are investigating electromagnets and collect the data found in the table below in a classroom experiment. They measure the strength of the magnetic field around their electromagnet.

Which of the following conclusions is supported by the data the students collected?

• Doubling the number of turns of wire in an electromagnet's coil will TRIPLE its strength.

• Doubling the number of turns of wire in an electromagnet's coil with DOUBLE its strength.

• Doubling the number of turns of wire in an electromagnet's coil with decrease its strength to ONE HALF.

• Doubling the number of turns of wire in an electromagnet's coil will have no effect on its strength.

The experiment pictured is that of a student passing a bar magnet through a coil of wire to demonstrate electromagnetic induction. Which conclusion can they draw from the data?

• An electric current is generated any time the magnet is moved into or out of the coil.

• An electric current is generated when the magnet is sitting inside the coil.

• An electric current is only generated when the magnet is moving to the right inside of the coil.

• An electric current is only generated when the magnet is moving to the left outside of the coil.

A student was asked to draw and describe a model for either an electric motor or generator. His description and model are below: "The model below shows a loop of wire which is being rotated between strong, permanent magnets by a person who is applying mechanical energy to turn the wire. As the loop of wire rotates, electrons begin to flow through it. The flow of electrons can be used to power a light bulb." What did the student describe?

• A motor

• A generator

• An electromagnet

• The description could be both a motor and a generator

A student conducted an experiment in which they used the same magnet to induce a voltage in three different coils as seen below. Based on the evidence in the image, which of the following conclusions can be drawn?

• There is an inverse relationship between the number of loops and the voltage that can be induced by the magnet.

• There is a direct relationship between the number of loops and the voltage that can be induced by the magnet.

• There is an inverse relationship between the size of the magnet and the voltage that can be induced by the magnet.

• There is no relationship between the number of loops in the coil and the voltage that can be induced by the magnet.

Why does adding an iron core to an electromagnet strengthen its magnetic force?

• The iron causes current to flow through the coil producing a bigger magnetic field.

• Current flows through the iron core and causes it to become magnetized creating a bigger magnetic field.

• The iron core transfers magnetic domains to the coil so that it can produce a bigger magnetic field.

• The magnetic domains inside the iron core are aligned when placed in the magnetic field of the coil and this created a bigger magnetic field.

The coils from electromagnets A, B, and C are shown below along with the amount of current passing through each one. Each electromagnet contains an identical iron core. Which electromagnet would have the strongest magnetic field at the point labeled P, near the end of the coil?

• Electromagnets "A" and "B" have the same number of loops so they will both have the strongest magnetic field. Electromagnet "C" has few loops so it will be weaker.

• Electromagnets "B" and "C" have the same amount of current flowing through them so they will both have the strongest magnetic field. Electromagnet "A" has less current flowing through it so it will be weaker.

• Electromagnet "B" has more loops and more current so it will have the strongest magnetic field. Electromagnet "A" will be weaker because it has fewer amps of current flowing and Electromagnet "C" has fewer loops, making it weaker.

• Electromagnets "A", "B", and "C" will all have the same magnetic field strength since the iron core inside the electromagnet is the same for all of them.

Think about the ways to increase or decrease the strength of an electromagnet. Using your knowledge of this relationship, choose the graph that best illustrates the strength of the magnetic field as current increases.

• Graph 1

• Graph 2

• Graph 3

• Graph 4

Which of the following diagrams would show an iron core that was placed inside of a current carrying wire coil or solenoid?

• A only

• B only

• C only

• A or C