physical science chapter 18
DESCRIPTION
physical science chapter 18 Magnets Pull iron (and some other metals) towards them. When small and allowed to rotate freely, always point north (compasses). physical science chapter 18TRANSCRIPT
![Page 1: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/1.jpg)
Magnetism
Physical ScienceChapter 18
![Page 2: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/2.jpg)
2
Magnets
• Pull iron (and some other metals) towards them.
• When small and allowed to rotate freely, always point north (compasses).
physical science chapter 18
![Page 3: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/3.jpg)
3
Magnetism
• A property of matter in which there is a force of repulsion or attraction between like or unlike poles.
• Related to electricity.
physical science chapter 18
![Page 4: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/4.jpg)
4
Magnetic poles
• The ends of magnets– Where the magnetic forces are strongest
• Like poles repel– North and north or south and south
• Opposite poles attract
physical science chapter 18
![Page 5: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/5.jpg)
5
Permanent magnets
• Naturally magnetic• Retain magnetic properties for long periods
of time.• Made of materials like iron, cobalt, and
nickel
physical science chapter 18
![Page 6: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/6.jpg)
6
Temporary magnets
• Formed by objects being near or rubbing against a permanent magnet
• Lose their magnetic properties soon after being separated from permanent magnet.
physical science chapter 18
![Page 7: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/7.jpg)
7
Magnetic field
• The area around a magnet where magnetic forces act.
• Strongest near the poles.
physical science chapter 18
![Page 8: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/8.jpg)
8
Compass
• Magnetic needle that rotates freely• Lines up with the Earth’s magnetic field.
physical science chapter 18
![Page 9: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/9.jpg)
Discuss
• Section 1 Review question #4 on page 624
9physical science chapter 18
![Page 10: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/10.jpg)
10
Creating magnetic fields
• An electric current causes a magnetic field.• The direction of the current affects the
direction of the magnetic field.
physical science chapter 18
![Page 11: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/11.jpg)
11
Electromagnets
• Magnets created by electric current flowing through wires
• When a wire is coiled into a solenoid, a strong magnetic field is created in the coil.
• Inserting an iron core inside the solenoid increases the magnetic field.
• See page 627
physical science chapter 18
![Page 12: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/12.jpg)
12
Galvanometer• Instrument used to detect
currents.• A coil of wire around an
iron core with a needle.• Between permanent
magnets.• When there is current in the
wire, the magnetic forces cause it to rotate, moving the needle.
physical science chapter 18
![Page 13: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/13.jpg)
13
Ammeters
• Galvanometers calibrated to measure current.
• Connected in series with the circuit.
physical science chapter 18
![Page 14: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/14.jpg)
14
Voltmeters
• Galvanometers calibrated to measure potential difference.
• Connected in parallel with the circuit
physical science chapter 18
![Page 15: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/15.jpg)
15
Electric motor
• Contains an electromagnet that can rotate.• Rotates between opposite poles of a
permanent magnet.• The current produces a magnetic field that
makes the coil turn.
physical science chapter 18
![Page 16: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/16.jpg)
16
Electric motor
• To keep the coil turning, the direction of the current in the coil must be reversed after every half turn.
• Done by a reversing switch called a commutator
physical science chapter 18
![Page 17: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/17.jpg)
17
Discuss
• Describe an electromagnet.• What is an instrument that can be used to
measure either current or potential difference?
• What does an ammeter measure?• What does a voltmeter measure?• What is a commutator?
physical science chapter 18
![Page 18: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/18.jpg)
18
Electromagnetic induction
• Moving a wire through a magnetic field produces a current in the wire
• You can also move a magnet through a coil of wire to produce a current in the wire
physical science chapter 18
![Page 19: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/19.jpg)
19
Generators
• Use electromagnetic induction to make current (electricity)
• A loop of wire is rotated in a magnetic field.• It needs mechanical energy to make it rotate
– Usually comes from burning fuel• Similar to an electric motor, but with the
opposite function
physical science chapter 18
![Page 20: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/20.jpg)
20
Direct current
• DC• From batteries• Current only flows in one direction in the
wire
physical science chapter 18
![Page 21: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/21.jpg)
21
Alternating current
• AC• Wall outlets• Current reverses direction in a regular
pattern• In US, reverses 120 times per second for
60 Hz alternating current• Most appliances have built in converters
that change AC to DC.
physical science chapter 18
![Page 22: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/22.jpg)
22
Transformer
• Increases or decreases the voltage of AC current
• Uses two coils with different numbers of turns
physical science chapter 18
![Page 23: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/23.jpg)
23
Step-down transformer
• Reduces voltage• Used between power lines and home
electrical circuits• High voltage electricity travels more
efficiently, but is not good for household appliances
physical science chapter 18
![Page 24: Physical Science Chapter 18](https://reader035.vdocuments.us/reader035/viewer/2022062401/5a4d1aec7f8b9ab05997b6de/html5/thumbnails/24.jpg)
24
Discuss
• Describe electromagnetic induction.• A generator operates by changing
_____________ energy into ____________ energy.
• Which kind of current reverses its direction in a regular pattern?
• Describe a step-down transformer.
physical science chapter 18