Energy and Electromagnetism

Why might an electromagnet be used to pick up old cars in junk yards?

• Electromagnets are powerful and can be turned on and off easily.

• Electromagnets are versatile and can pick up any metallic objects in the yard.

• Electromagnets are easy to operate and can be run by cheap labor.

• Electromagnets are inexpensive and easily create revenue.

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In an electric motor, an electric current causes the coil to rotate, changing

• mechanical energy to potential energy

• mechanical energy to electrical energy

• electrical energy to mechanical energy

• electrical energy to potential energy

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An electromagnet used in a junk yard can only pick up small cars. How could the electromagnet be improved so that it can lift trucks and other large vehicles?

• The electric current could be increased and the number of coils in the solenoid could be decreased.

• The electric current and the number of coils in the solenoid could be increased

• The electric current could be decreased and the number of coils in the solenoid could be increased

• The electric current and the number of coils in the solenoid could be decreased.

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The balloon shown above rearranges the charges in the wall without actually touching the wall. This is an example of

• conduction

• induction

• friction

• convection

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How does a material become positively charged?

• by gaining protons

• by gaining electrons

• by losing electrons

• by losing protons

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Which method of charging occurs when electrons move from one object to another by direct contact (when touching)?

• friction

• conduction

• induction

• indirectly

Mrs. Smith's class decides to try an experiment. She rubs a blown up balloon on Sandy's head. After this, she takes the balloon and places it on the side of the wall, where it sticks, instead of falling to the ground. Also, Sandy's hair is now sticking almost straight out.

What is the reason the balloon is now sticking to the wall?

• The balloon has a static electric charge from rubbing Sandy's hair.

• The wall has been electrically charged and so attracts the balloon.

• The balloon lost its static electric charge by rubbing Sandy's hair.

• The balloon would have stuck to the wall whether or not it was rubbed on Sandy's hair.

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A table has several directional compasses, several lengths of wire, an iron nail, a battery, a light bulb, a permanent magnet, several metal paper clips and a rubber eraser.

A student is asked to build and demonstrate a working temporary magnet. From the items on the table, which ones can be used together to accomplish this task?

• a battery, an iron nail, a wire and several paper clips

• a light bulb an iron nail, a wire and several paper clips

• a battery, a compass, a permanent magnet and several paper clips

• a battery, an iron nail, a permanent magnet and several paper clips

The region around a magnet in which the magnetic forces can act is called the

• solenoid

• domain

• pole

• magnetic field

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If a material does not allow charges to move through it easily, what is it called?

• electrical conductor

• electrical insulator

• electric discharge

• static electricity