Unit 5 Review: Electricity and Magnetism

This is a kind of electroscope student made in science class to study charges.Student Procedure:~Tear off two pieces of tape, each 4 inches (10 cm) long.~Press each piece firmly on the work table leaving one end of each tape piece sticking up as a handle.~Quickly pull the tapes from the table and stick one piece on the arm of a straw in one film canister, and the other piece on the arm of a straw in the other film canister.~Move the canisters so the two pieces of tape are face to face, about 6 inches apart.~Slowly move the canisters closer together.

Ms. Mann's experiment illustrates several important facts in science that include ALL BUT ONE of those listed here.

• Friction can cause a transfer of charge.

• Attractive forces can work at a distance.

• Opposite charges repel.

• Like charges repel.

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A group of students is experimenting on force fields, investigating magnetism. One group student set up the demonstration you see here. "Oh wow!" Sarah exclaimed. "It's magic!" Is it magic? Which statement best explains how the center magnet is able to hover between two other magnets?

• The opposite poles of each magnet are facing each other so they repel.

• The magnets are stacked so that like poles are facing one another.

• The middle magnet is attracted to the top magnet but pulled down by gravity.

• The middle magnet is repelling the top magnet while attracting the bottom.

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Force at a Distance

A force is a push or a pull. Forces occur when objects interact. There are two groups of forces: contact forces and forces-at-a-distance. Contact forces are forces that result when two interacting objects are in physical contact with each other. Examples include friction, air resistance, and applied forces. Forces-at-a-distance are forces that result even when the two objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravity, magnetism, and electrostatics.

During induction, a positively charged rod is brought near to but not touching the electroscope. The presence of the charged object above the plate of the electroscope induces charges to move down into the gold leaves, giving the electroscope an overall positive charge. The positive leaves repel. Describe the force(s) at work.

• Opposites attract, contact force, followed by like charges repel, contact force.

• Opposites attract, force-at-a-distance, followed by like charges repel, contact force.

• Like charges repel; force-at-a-distance.

• Opposites attract, force-at-a-distance, followed by like charges repel, force-at-a-distance.

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Two identical isolated conducting spheres are picked for an experiment. Only one of them is charged. If the spheres are now briefly brought into contact and then separated by a small distance, the two spheres would experience

• a force of repulsion, because they are like-charged.

• no force, because charges are not transferred by mere contact.

• a force of attraction, because they are oppositely charged.

• no force, because the distance separating the spheres needs to be large.

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Anna learned that every magnet has a north and a south end called poles. She notices that when she puts the north end of a magnet near the south end of another magnet, they pull together. What can Anna conclude from her observation?

• Opposite poles of magnets attract.

• The north pole picks up iron nails.

• Only the north pole has an attractive force.

• Opposite poles of magnets repel.

You may have seen what a magnet will do to iron filings, arranging them into specific patterns like the one you see here. This arrangement is due to the ____________ that is produced by the magnet.

• vibration

• magnetic impulse

• force field

• magnetic field

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This picture shows a standard electric field created by a point charge. This electric field will influence

• objects with a negative charge.

• any object with a mass greater than zero.

• objects with a positive charge.

• both positively and negatively charged objects.

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This diagram shows the electric field created by two parallel charged plates. As you can see, with this set up, the electric field lines run from left to right. When let go within this electric field, what type of particle would drop straight down?

Responses

• a neutron

• a proton

• an ion

• an electron

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If you have ever used a compass, you know that it can be used to help navigate. It does this with a needle that always points north, so you know which direction you are heading. Why does a compass needle point north?

• Due to the direction of the earth's orbit.

• Due to the influence of the earth's magnetic field.

• Due to the influence of the earth's rotation.

• Due to the influence of the earth's electric field.

The distance between a proton and an electron is cut in half. How does the force of attraction change?

• The force becomes twice as much.

• The force becomes four times as much.

• The force becomes one-half as much.

• The force becomes one-quarter as much.

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