Electricity & Magnetism

An electromagnet picks up an entire pile of paper clips as soon as it is turned on.

Which of the following might allow the electromagnet to pick up a single paper clip at a time?

• increasing the distance between the electromagnet and the paper clips

• removing the iron nail from the core of the electromagnet

• increasing the number of loops in the electromagnet's coil

• increasing the number of batteries supplying voltage to the electromagnet

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You try to pick up a small bit of plastic wrap that is on your desk.

Your hand has a positive charge.

The piece of plastic has a positive charge.

What will happen when your hand gets close to the plastic?

• The plastic will stick to your hand.

• The plastic will move towards your hand.

• The plastic will move away from your hand.

• The plastic will circle around your hand.

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A solenoid is a coil of wire that produces a magnetic field when carrying an electric current. The strength of the magnetic field produced by a solenoid can be increased in two basic ways: increasing the number of loops in the solenoid or increasing the amount of current running through the solenoid. A solenoid's magnetic field can be increased to an even greater degree by wrapping the wire around a material that can be magnetized. Four solenoids are shown below.

Based on the strength of the magnetic fields they produce, choose the STRONGEST solenoid.

• Solenoid A

• Solenoid B

• Solenoid C

• Solenoid D

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A solenoid is a coil of wire that produces a magnetic field when carrying an electric current. The strength of the magnetic field produced by a solenoid can be increased in two basic ways: increasing the number of loops in the solenoid or increasing the amount of current running through the solenoid. A solenoid's magnetic field can be increased to an even greater degree by wrapping the wire around a material that can be magnetized. Four solenoids are shown below.

Based on the strength of the magnetic fields they produce, choose the WEAKEST solenoid.

• Solenoid A

• Solenoid B

• Solenoid C

• Solenoid D

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NGSS.MS-PS2-3

When you rub a balloon against her hair electrons from your hair travel to the balloon, giving the balloon a negative charge and her hair a positive charge.

When the negatively charged balloon is brought near the strands of your hair, they move to get closer to the balloon, without the balloon actually touching them. This shows that

• particles in the air must be pulling your hair toward the balloon.

• electric attraction is a force that can act at a distance.

• your hair would move in this way with or without the balloon.

• electric attraction is a force that can only act on contact.

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Henry sets his keys on a wooden table.

He then takes a powerful magnet and positions it below the table and the keys. He finds that he is able to drag the keys along the table by moving the magnet.

This demonstrates that

• gravity is proportional to mass.

• magnetic forces act on wooden objects.

• magnetic forces act at a distance.

• gravitational forces are contact forces.

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The electromagnet shown below is made up of a coil of electrical wire wrapped around an iron core.

Which of the following would DECREASE the strength of this electromagnet?

• removing its iron core

• increasing the current through the coil

• increasing the number of wire loops in the coil

• adding batteries to the circuit

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After walking across a carpeted floor in socks, you bring your finger near a metal door knob and you get shocked.

This demonstrates that

• frictional forces act at a distance.

• frictional forces require direct contact.

• electric forces can act at a distance.

• electric forces require direct contact.

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NGSS.MS-PS2-5

You bring a magnet near a metal object. A magnetic force acts on an object, pulling it upward.

Which of the following best describes the magnetic force?

• a frictional force

• a contact force

• a force that acts at a distance

• a gravitational force

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The Earth has a magnetic field around it, which is generated by its molten core. This magnetic field exerts a force on compass dials, which are magnets, causing them to align with the Earth's magnetic field.

This force on compass dials is an example of a force that _______.

• acts only on contact.

• needs electricity to act.

• acts through particles in the air.

• acts at a distance.

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