Electromagnetism Electromagnetism

Galvanometers A galvanometer is a device used to measure
current through the interaction of an electromagnet and a permanent
magnet. Galvanometers are sometimes found in equipment
used by electricians, such as ammeters and voltmeters.
Galvanometers contain an electromagnet placed between the
poles of a permanent magnet. The electromagnet is free to rotate
and is attached to a pointer. The pointer moves along a scale
that shows the size and direction of the current. When there
is a current in the coil of the electromagnet, the poles of the
electromagnet are repelled by the poles of the permanent
magnet. Figure 19 shows how the parts of a galvanometer work.
REVIEW
Scale Pointer Electromagnet
S
20
10 0 10
20
30 30
1. Describe what happens when you hold a compass close
to a wire carrying a current.
2. How is a solenoid like a bar magnet?
3. What makes the armature in an electric motor rotate?
4. Explain how a solenoid works to make a doorbell ring.
5. Applying Concepts What do Hans Christian Oersted’s
experiments have to do with a galvanometer? Explain
your answer.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
N
Permanent magnet
Figure 19 The pointer will move
farther when there is a large current
in the electromagnet than
when there is a small current.
NSTA
TOPIC: Electromagnetism
GO TO: www.scilinks.org
sciLINKS NUMBER: HSTP440
Electromagnetism 467