Electric and Magnetic Forces

Which of the two below result in an attractive force?

• A positive charge and a negative charge

• Two negative charges

• Two south poles

• A north pole and a south pole

• Two postive charges

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Static electricity is the buildup of charges between two objects. What best explains why a balloon is attracted to hair when the two have been rubbed together?

• The balloon and hair both have positive charges

• The balloon and the hair both have negative charges

• The balloon and the hair both have neutral charges

• The balloon and the hair both have opposite charges

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Which of the following most closely resembles an electromagnetic?

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• 
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Two bar magnets are held close together. They are released and allowed to move freely. The bar magnets quickly come together. Which best explains why this happens?

• The poles facing one another are both south poles

• The poles facing one another are both north poles

• The poles facing one another are opposite poles

• One magnet was bigger than the other

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Frederick sets paper clips out on a table. He then takes a magnet, places it directly beneath the paper clips under the table, and moves the magnet. He finds that the paper clips move with the magnet. Why does this happen?

• Magnetic force is a repellant force

• Magnetic forces act on wood, like in the table

• The paper clips are feeling the gravitational force of the magnet

• Magnetic forces act at a distance, even betwewn objects

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Surrounding each magnetic is an invisible force field called

• Gravity

• A magnetic field

• An electric field

• The Force

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In an electromagnet, coils of wire are wrapped around a magnetic object to generate a magnetic field. What the is relationship between number of coils and the strength of the magnetic field?

• The more coils an electromagntic has, the stronger the magnetic field

• The more coils an electromagntic has, the weaker the magnetic field

• The larger the metal object, the stronger the magnetic field is

• There is no relationship between number of coils and the strength of a magnetic field

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To decrease the strength of a magnetic field around an electromagnet, we must

• increase the number of coils

• increase the size of the iron core

• decrease the size of the iron core

• decrease the number of coils

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What is the cause of electricity?

• Magnetism

• Gravity

• Moving electrons

• Lightning

A Van der Graff generator works by

• Causing the outside of the metal ball to become positively charged

• Causing the outside of the metal ball to become neutrally charged

• Causing the outside of the metal ball to become a bar magnet

• Causing the outside of the metal ball to become negatively charged

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