Physical Science Chapter 18 Magnetism Physical Science Chapter 18

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 18

physical science chapter 18 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

physical science chapter 18 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

physical science chapter 18 Permanent magnets Naturally magnetic Retain magnetic properties for long periods of time. Made of materials like iron, cobalt, and nickel physical science chapter 18

physical science chapter 18 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

physical science chapter 18 Magnetic field The area around a magnet where magnetic forces act. Strongest near the poles. physical science chapter 18

physical science chapter 18 Compass Magnetic needle that rotates freely Lines up with the Earth’s magnetic field. physical science chapter 18

physical science chapter 18 Discuss Section 1 Review question #4 on page 624 physical science chapter 18

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

physical science chapter 18 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

physical science chapter 18 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

physical science chapter 18 Ammeters Galvanometers calibrated to measure current. Connected in series with the circuit. physical science chapter 18

physical science chapter 18 Voltmeters Galvanometers calibrated to measure potential difference. Connected in parallel with the circuit physical science chapter 18

physical science chapter 18 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

physical science chapter 18 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

physical science chapter 18 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

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

physical science chapter 18 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

physical science chapter 18 Direct current DC From batteries Current only flows in one direction in the wire physical science chapter 18

physical science chapter 18 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

physical science chapter 18 Transformer Increases or decreases the voltage of AC current Uses two coils with different numbers of turns physical science chapter 18

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

physical science chapter 18 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