Spring Interim Review

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

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

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

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.

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

• A) A only

• B) B only

• C) C only

• D) A or C

In the electric motor shown below, an electric current causes the coil to rotate. What type of energy conversion takes place in an electric motor?

• Magnetic energy to electrical energy

• Electrical energy to magnetic energy

• Potential energy to electrical energy

• Electrical energy to mechanical energy

A 2.1 kW-hr dishwasher is run for 1.5 hours each day. The power company charges $0.13 per kW-hr. How much would it cost to run the dishwasher for 30 days?

• $8.19

• $12.29

• $81.90

• $99.65

A 2.1 kW dishwasher is run for 1.5 hours each day. The power company charges $0.13 per kW-hr. How much would it cost to run the dishwasher for 30 days?

• $8.19

• $12.29

• $81.90

• $99.65

A student rubs two balloons with fur and notices that they repel when brought near each other. What would happen if he tried to bring the balloons even closer to each other?

• The balloons will gain a neutral charge

• The balloons will now attract

• The balloons will repel each other with a greater amount of force

• The balloons will repel each other with less force

A plastic comb becomes negatively charged when you comb through your hair. What type of charge would your hair have after combing it?

• No charge (neutral)

• Negative Charge

• Positive Charge

• Polarized charge

Which answer most completely describes the difference/s between the gravitational force and the electrostatic force?

• The gravitational force is stronger and can attract or repel while the electrostatic force is weaker and can only attract.

• The gravitational force is stronger and can only attract while the electrostatic force is weaker and can both attract and repel.

• The gravitational force is weaker and can attract or repel while the electrostatic force is stronger and can only attract.

• The gravitational force is weaker and can only attract while the electrostatic force is stronger and can both attract and repel.