# Chapter 9 Magnets and currents

Flashcards by Millie Berrett, updated more than 1 year ago
 Created by Millie Berrett almost 6 years ago
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### Description

Cambridge IGCSE and GCSE Science (Physics) Flashcards on Chapter 9 Magnets and currents, created by Millie Berrett on 31/10/2014.

## Resource summary

 Question Answer Properties of magnets? -Has a magnetic field around it -Has two opposite pole (N and S) -Will attract magnetic materials by inducing magnetism in them -Will exert little or no force on a non magnetic material 2 of the same pole will? 2 opposite poles will? Like poles repel, unlike poles attract the closer the poles the greater the force between them How can you make a magnet? BEST WAY is to use electricity -Stroke the iron with a magnet (this makes all the domains follow the magnet) -Hammer the metal (the domains turn the same way) How do you demagnetize something? BEST WAY is to use alternating current -Hammer the object -Heat up the object Properties of soft iron? Soft iron is easy to magnetize but loses its magnetism very easily How can field lines be shown? Field lines can be shown using iron filings sprinkled over a piece of magnet on top of a magnet How can field lines be shown around a magnet? -The field lines run from the N to the S -The magnetic field is strongest where the the lines are closest together What is the rule for field direction? The direction of the magnetic field produced by a current is given by the right hand grip rule. How can you make a magnetic field stronger? -Add more coils -Increase the current -wrap the coil around a soft iron core What is a long coil of wire called? A long coil is called a SOLENOID How could you change the poles? -Turn the coils the other way -Reverse the current What is an electromagnet and how is is different form a normal magnet? An electromagnet is coils with a current flowing through them. Unlike an ordinary magnet, an electromagnet can be switched on and off. What is a magnetic relay? A magnetic relay is a switch operated by an electromagnet. With a relay a small switch can be used to turn on a much more powerful circuit. How does a magnetic relay work? When the switch in the input circuit is closed a current flows through the electromagnet. This pulls the iron armature towards it, which closes the contacts. As a result a current flows through the motor. What is Fleming's left-hand rule? If you hold the thumb and first two fingers of your left hand at right angles, and point the fingers as shown, the thumb gives the direction of the force How does a simple dc motor work? The coil can rotate between the poles of the magnet, The communicator rotates with the coil. The brushes keep the coil connected to the battery Image: dc_motor.jpg (image/jpg) How can the turning effect on the coil be increased? -Increasing the current -Using a stronger magnet -Increasing the number of turns in the coil -Increasing the area of the coil How do you induce a current in a coil? You move a magnet into a coil. This cause a voltage to be induced in the coil. The magnetic fields are moving How can the induced voltage be increased? -moving the magnet faster -using a stronger magnet -increasing the number of turns on the coil What is a transformer? A transformer can be used to increase or decrease AC voltages How does a transformer work? When alternating current flows through the Primary coil, it sets up an alternating magnetic field in the core and secondary coil. This induces an alternating voltage in the output coil. What is the turns ratio What is a step up transformer? Step up transformers have more turns on the output coil than on the input coil, so their output voltage is more than the input voltage. Step up transformers are used in power stations. What is a step down transformer? Step down transformers have fewer turns on the output coil than on the input coil so the output voltage is less than the input voltage. In battery chargers, computers and other electrical equipment they are used to reduce the voltage of the AC mains What is the equation for power through a transformer? Input voltage x input current= output voltage x output current V1xI1=V2xI2

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