electricity and magnetism

discovery of electromagnetism

In 1820, a physicist in Denmark, named Hans Christian Oersted, discovered how electric currents and magnetic fields are related. However, it was just a lucky accident. Oersted, who is pictured in Figure 25.1, was presenting a demonstration to his students. Ironically, he was trying to show that electricity and magnetism are not related. He placed a wire with electric current flowing through it next to a magnet, and nothing happened. After class, a student held the wire near the magnet again, but in a different direction. To Oersteds surprise, the pointer of the magnet swung toward the wire so it was no longer pointing to Earths magnetic north pole. Oersted was intrigued. He turned off the current in the wire to see what would happen to the magnet. The pointer swung back to its original position, pointing north again. Oersted had discovered that an electric current creates a magnetic field. The magnetic field created by the current was strong enough to attract the pointer of the nearby compass. Oersted wanted to learn more about the magnetic field created by a current, so he placed a magnet at different locations around a wire with current flowing through it. You can see some of his results in Figure 25.2. They show that the magnetic field created by a current has field lines that circle around the wire. You can learn more about Oersteds investigations of current and magnetism at the URL below. MEDIA Click image to the left or use the URL below. URL:

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electric currents and magnetic fields

The magnetic field created by a current flowing through a wire actually surrounds the wire in concentric circles. This magnetic field is stronger if more current is flowing through the wire. The direction of the magnetic field also depends on the direction that the current is flowing through the wire. A simple rule, called the right hand rule, makes it easy to find the direction of the magnetic field if the direction of the current is known. The right hand rule is illustrated in Figure 25.3. When the thumb of the right hand is pointing in the same direction as the current, the fingers of the right hand curl around the wire in the direction of the magnetic field. You can see the right hand rule in action at this URL: .

instructional diagrams

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questions

Oersted was the scientist who discovered how

a. a magnetic compass works.

b. magnetism causes an electric current.

-->  c. electricity and magnetism are related.

d. electric charges flow through a wire.

material through which electric current can flow

a. electromagnetism

b. compass

c. right hand rule

d. electric current

-->  e. electric conductor

To use the right hand rule, you should point your thumb in the same direction as the

a. voltage source.

b. magnetic field.

-->  c. electric current.

d. none of the above

continuous flow of electric charges

a. electromagnetism

b. compass

c. right hand rule

-->  d. electric current

e. electric conductor

device that points toward a north magnetic pole

a. electromagnetism

-->  b. compass

c. right hand rule

d. electric current

e. electric conductor

Assume that a wire is connected to a battery so current is flowing through the wire. If you place a compass near the wire, the needle of the compass will point toward

-->  a. the wire.

b. the battery.

c. your thumb.

d. none of the above

way to find the direction of the magnetic field around a wire carrying electric current

a. electromagnetism

b. compass

-->  c. right hand rule

d. electric current

e. electric conductor

If you disconnect one end of the wire in question 3 from the battery, the compass needle will point toward

a. the loose end of the wire.

-->  b. Earths north magnetic pole.

c. the fingers of your right hand.

d. the end of the wire still attached to the battery.

If you increase the amount of current flowing through a wire, the magnetic field around the wire will

a. remain the same.

b. change direction.

-->  c. increase in strength.

d. decrease in strength.

magnetism produced by electric current

-->  a. electromagnetism

b. compass

c. right hand rule

d. electric current

e. electric conductor

Oersteds discovery of the connection between electric currents and magnetic fields was a lucky accident.

-->  a. true

b. false

Moving electric charges generate a magnetic field.

-->  a. true

b. false

When you apply the right hand rule, your thumb points in the direction of the magnetic field.

a. true

-->  b. false

Oersted discovered electromagnetism when he placed a compass near a battery.

a. true

-->  b. false

The direction of the magnetic field around a wire is parallel to the direction of the current through the wire.

a. true

-->  b. false

The direction of the magnetic field around a wire carrying current is the same as the direction of the current.

a. true

-->  b. false

A compass can be used to find the direction of a magnetic field around a current-carrying wire.

-->  a. true

b. false

The magnetic field around a wire is stronger when more current is flowing through the wire.

-->  a. true

b. false

The magnetic field created by current flowing through a wire surrounds the wire in concentric circles.

-->  a. true

b. false

The magnetic field Oersted created around a wire was too weak to affect a nearby compass.

a. true

-->  b. false

A compass always points to Earths north magnetic pole even when placed near a magnet.

a. true

-->  b. false

The right hand rule states that you should always hold a compass in your right hand.

a. true

-->  b. false

Oersted discovered that electric currents generate magnetic fields in

a. 1600.

-->  b. 1820.

c. 1980.

d. 2000.

When Oersted made the discovery in question 1, he was trying to demonstrate that

-->  a. electricity and magnetism are not related.

b. electric currents create magnetic fields.

c. compasses can detect magnetic fields.

d. magnetic fields create electric currents.

The magnetic field created by current flowing through a wire

-->  a. surrounds the wire in concentric circles.

b. is just like the magnetic field of a bar magnet.

c. has the same direction as the current.

d. has the opposite direction to the current.

According to the right hand rule, the fingers of the right hand curl around the wire in the same direction as the

a. current.

b. compass.

c. conductor.

-->  d. magnetic fiel

Factors that affect the magnetic field around a wire that is carrying current include

a. amount of current.

b. direction of current.

c. position of compass.

-->  d. two of the above

diagram questions

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