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GCSE Physics (Additional GCSE) Mind Map on Electricity, created by seth.bragg on 04/20/2014.

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Created by seth.bragg over 5 years ago
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1 Static Electricity
1.1 When you rub two different insulating materials against each other they become electrically charged
1.1.1 This happens because negatively charged electrons move from on material to the other The material that loses electrons becomes positively charged The Material that gains the electrons becomes negatively charged Two charged objects will repel each other if the charges are the same and attract each other if opposite
2 Current and Voltage In Electrical Circuits
2.1 Circuit Symbols


2.2 For a circuit to work, two things are important
2.2.1 There must be a complete circuit A complete circuit is one without any gaps
2.2.2 There must be no short circuits Short circuits are ways of getting past the lamp without going through another component
2.3 Series and Parallel circuits
2.3.1 Series circuits are circuits where each component is connected one after the other in a single loop The current that flows across the components is the same
2.3.2 Parallel circuits are circuits where components are connected in separate loops The current is shared between each component connected in parallel
2.4 Electric current:
2.4.1 a flow of electric charge No current can flow if the series is broken Current is measured in amps (A) and it is measured using an ammeter which is connected in series with a component The size of an electric current is the rate of flow of electric charge It is calculated as: I = Q ÷ t Where I is current (A), Q is charge in Coulombs (C) and t is time in seconds
2.4.2 When more cells are added to a circuit p.d. increases so more current can flow
2.5 Potential Difference
2.5.1 Potential Difference, or voltage is needed to make current flow and is often provided by cells or batteries It is measured in volts, V The potential difference across a component in a circuit is measured using a voltmeter which is connected in parallel The potential difference between two points in an electric circuit is the work done when a coulomb of charge passes between the points It is calculated as: V = W ÷ Q Where V is p.d. (V), W is work done in joules (J) and Q is charge (C)
2.5.2 A typical cell produces 1.5V If two or more cells are connected in series their p.d. is the sum of the two values If their are connected in opposite directions then they are subtracted e.g. to cells in opposite directions will produce a p.d. of 0V meaning no current can flow
3 Resistance
3.1 There is a resistance to the flow of an electric current through most conductors which increase as the length of the wire increases or the thickness of the wire decreases
3.1.1 The moving electrons can collide with ions in the metal wire which makes it more difficult to flow which causes resistance The resistance of a long wire is greater than that of a short wire because electrons collide more The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current As the temperature increases the metal ions vibrate more so there are more collisions and the resistance increases
3.1.2 Resistance can of a component can be found by measuring the current flowing through it, and potential difference across it The equation used to calculate this is V = I × R which can be rearranged as R = V ÷ I Where V is potential difference, I is Amps and R is resistance in ohms, Ω
3.2 The current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it
3.3 The resistance of a lamp increases as the temperature of its filament increases. The current flowing through a filament lamp is not directly proportional
3.4 The diode has a very high resistance in one direction which means that the current can only flow in the other direction
3.5 A light-emitting diode, LED, produces light when a current flows through it in the forward direction. LEDs are often used for indicator lights in electrical equipment such as computers and television sets. As LEDs use a much smaller current than other types of lighting, their use is increasing.
3.6 Thermistors are used as temperature sensors - for example, in fire alarms. Their resistance decreases as the temperature increases:
3.6.1 At low temperatures, the resistance of a thermistor is high and little current can flow through them
3.6.2 At high temperatures, the resistance of a thermistor is low and more current can flow through them
3.7 LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases:
3.7.1 In the dark and at low light levels, the resistance of an LDR is high and little current can flow through it
3.7.2 In bright light, the resistance of an LDR is low and more current can flow through it
4 Household Electricity
4.1 AC and DC
4.1.1 Direct Current is current that only flows in one and it is supplied by batteries and cells On an oscilloscope Direct Current would have a straight line
4.1.2 Alternating current is current that constantly changes direction and it is supplied by mains plugs On an oscilloscope an Alternating current would show a wave
4.2 Cables and Plugs
4.2.1 A mains electricity cable has two or three inner wires made of copper, because copper is a good conductor, and covered by plastic, because it is a good insulator The inner wires are colour: blue is neutral, brown is live, and thee green and yellow stripey wire is earth
4.2.2 The features of a plug are A plastic or rubber case because they are both good insulators Three pins are made from brass, which is a good conductor of electricity A fuse between the live terminal pin which breaks the circuit if too much current flows The cable is secured in the plug by a cable grip
4.2.3 To remember where each of the wires go: b(L)ue is (L)eft, b(R)own is (R)ight, and s(T)riped is (T)op
4.3 Fuses
4.3.1 Fuses protect electrical circuits and appliances by breaking if a fault in an appliance causes too much current to flow The fuse contains a metal wire which melts easily, if the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit Fuses are made in standard ratings such as 3A, 5A and 13A A suitable fuse is one that should melt just above the appliance's working current, for example: if the device works at 3A use a 5A fuse
4.3.2 Circuit breakers also protect circuits by detecting a difference in current between the live and neutral wires They work much faster than fuses and don't need replacing, just turning on again
4.4 Earthing
4.4.1 Many electrical appliances have metal cases; the earth wire creates a safe route for the current to flow if the live wire touches the casing You would get an electric shock if the live wire inside an appliance came loose and touched the metal casing The earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock A strong current surges through the earth wire because it has a very low resistance breaking the fuse and disconnecting the appliance Some appliances do not have earth wires this is because they have a plastic casing and there is no threat of an electric shock
5 Charge, Current and Power
5.1 Choosing appliances
5.1.1 Some appliances are more efficient at transferring energy than others For example less energy is wasted as heat energy from energy-saving, such as LEDs, and compact fluorescent lamps (CFLs) than from filament lamps
5.1.2 Filament lamps contain a thin metal filament that glows when electricity passes through it, however, most of the electrical energy is transferred as heat energy instead of light energy so it is innefficient Modern energy-saving lamps work in a different way; they transfer a greater proportion of electrical energy as light energy so is more efficient than the filament bulb
5.2 Power
5.2.1 Power is a measure of how quickly energy is transferred; the unit of power is watts, W The more energy that is transferred in a certain time the greater the power Power is calculated as P = E ÷ t Where P is power (W), E is energy transferred (J) and T is time (S) To calculate the power in an electrical appliance use P = I × V Where P is power (P), I is the current (A) and V is potential difference (V)