Magnetism

A group of students conducted an activity for science class. They used a galvanometer, which is an instrument that can detect an electric current. They followed these steps: 1. Obtain a 100 foot long electrical extension cord. 2. Connect each end of the extension cord to the galvanometer. 3. Using duct tape, secure part of the extension cord to the ground as shown below. 4. Swing the top part of the extension cord as if a person were to enter to jump rope. 5. Have a student observe the galvanometer while the cord is rotating. Students observed that the needle of the galvanometer moves. What does this demonstrate?

• Moving an electrical conductor through Earth's magnetic field induces an electric current.

• Moving an electrical conducting wire close to the ground changes Earth's magnetic field.

• Moving an electrical conducting wire through a magnetic field changes the wire's conductivity.

• Moving an electrical conductor next to an electric current produces a magnetic field.

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How could Theresa cause an electric current to flow through one of the copper wires?

• Move the magnet up and down near one of the coils.

• Remove a length of wire from one of the coils.

• Carefully touch the magnet to one of the coils.

• Disconnect the coils and place them side by side.

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How does the electromagnet cause the beater bar to move?

• The electromagnet repeatedly bangs into the beater bar, causing the beater to repeatedly strike the bell.

• An electric current flows through the electromagnet's wire coil and generates a magnetic field, which produces a force on the beater bar.

• An electric current flows through the electromagnet, into the beater bar, and into the bell, causing it to ring.

• An electric current flows through the bell, which electrically charges the beater bar and the electromagnet, causing it to vibrate.

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Why do the magnetic forces acting on the coil change as the current running through the coil changes?

• because the current generates a magnetic field around the coil

• because the current causes the magnet to lose power

• because coils of wire are not usually attracted to magnets

• because the current causes the magnet to gain power

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Label the parts of the electromagnet.

a

b

c

d

iron core

wire

voltage source

solenoid

Which of these is a way to make an electromagnet stronger?​ ​ ​ ​ (a)  

• wrapping the wire around the iron core more

• putting a switch in the electrical circuit

• replacing the copper wire with plastic wire

• replacing the iron core with a copper core

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Why is it necessary for the wire to be rotated?

• Its motion when it moves upward changes gravity into magnetism

• Its motion through the magnetic field creates a current in the wire.

• Its motion removes the magnetic field by using up the magnetic energy.

• Its motion through the air transforms heat into magnetism

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Many bicycles have generators that have a light that can be powered without a battery. Instead of a battery, a magnet and a coil of wire are used to make an electric current flow. The setup shown below models how a bicycle generator functions to produce light. Currently, no electric current is flowing through the circuit shown.

What needs to happen to cause an electric current to flow through the circuit?

• The magnet's north pole needs to point up.

• A smaller wire needs to be used.

• A bigger light bulb needs to be used.

• The magnet needs to be in constant motion.

Which of the following explains how a generator produces electricity?

• A static magnetic field produces alternating current

• An electromagnetic field converts electrical energy to magnetic energy.

• A moving magnetic field generates an electrical current.

• An unstable electric field produces electrical sparks.

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A generator converts mechanical energy to electrical energy. When a coil placed between two magnets rotates, the magnetic lines of force are disturbed. This induces a current in the coil.

What could be done to make the lamp less bright?

• use a lamp that lights up with a lower current

• turn the coil faster

• increase the strength of the magnets

• move the magnets farther from the coil

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