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Electricity

• Things can be charged by rubbing them. There are 2 kinds of charge: positive (+) and negative (-).
• Two + charges or two - charges repel each other. A + charge attracts a - charge.
• An uncharged (neutral) object has equal amounts of + and - charges.
• An electric current is the flow of charge (electrons). It is measured in amps (A).
• The circuit symbols for a battery, switch, ammeter, voltmeter, etc.
• A bi-metallic strip bends when it is heated. this is because the 2 metals expand by different amounts.
• An electronic system has 3 parts: input (sensor), processor, output.
• A digital system has definite steps, often only two steps (OFF and ON). These are called logic 0 and logic 1. An analogue system can change smoothly with no definite steps.
• Sensors include the eye, a micro-switch, a tilt switch, a reed switch, a moisture sensor, a microphone, a light-dependant resistor (LDR) and a thermistor.
• Output devices include: a lamp, an LED (light emitting diode), a motor, a buzzer and a loudspeaker.
• A relay uses an electromagnet. it uses a small current to control a large current.
• Logic gates can make decisions. There are 3 kinds of logic gate: NOT, AND, OR.
• In a NOT gate, the output is signal is NOT the same as the input signal.
• In an AND gate the output signal is 1 (ON) only if the first input is 1 AND the second input is 1.
• In an OR gate the output is 1 if the fist input is 1 OR the second input is 1.

What you should be able to do.

• Investigate the attraction and repulsion of electric charges.
• Explain what is happening in experiments with the Van de Graff generator.
• Draw circuit diagrams for series and parallel circuits.
• Use a variable resistor and an ammeter.
• Make a fire alarm using a bi-metallic strip.
• Use a voltmeter correctly.
• Write a message in Morse Code and send it to a friend.
• Use a reed switch to switch a current on and off.
• Use an LDR (light dependant resistor) to vary a current.
• Investigate how a current through a thermistor depends on the its temperature.
• Use an electronics board to switch a lamp or a buzzer on and off.
• Use NOT, AND OR gates to solve problems.
• Draw systems diagrams to show how logic gates are connected.