P2: Electricity Booklet 1 Name: _______________________ Teacher: _______________________ You are reminded for the need to complete all work to the best of your ability and the need for good presentation throughout.

What is meant by resistance? Anything in the circuit that slow the flow of current. The equation for resistance is Resistance (Ω) = Potential Difference (V) Current (A) A voltage-current graph for a ‘filament lamp’: I V This is a curve because as temperature increases, the resistance increases. A voltage-current graph for a ‘diode’: I V This is a shaped like this because current only flows in ONE direction. A voltage-current graph for a ‘wire’ at constant temperature: I V This is a straight line because current is directly proportional to voltage. Why does the resistance in a wire increase with temperature? As temperature increases, resistance increases at the particles gain more kinetic energy and so move around move and make it harder for the electrons to flow. The resistance on a voltage-time graph is shown by? Gradient of the graph. The steeper the gradient, the more current flows, so the lower the resistance.

What is a variable resistor? A device which is capable of changing the resistance in the circuit. What is a Diode? A device which allows current to only flow in one direction as there is a very high resistance in the other direction. What is a LDR? A device where light affects the resistance. In darkness the resistance is high, in light the resistance if low. What is a Thermistor? A device where heat affects the resistance. In cool conditions the resistance is high, in hot conditions the resistance if low. A RESISTANCE graph for a ‘LDR’: R DARKLIGHT This is a curve because.. In dark, the resistance is higher than in light. This is used for automatic night lights and burglar alarms, A RESISTANCE graph for a ‘thermistor’: R COOL HOT This is a curve because.. In cool conditions the resistance is higher than in hot. This is used in car engines sensors and thermostats in houses.

What is meant by resistance? Anything in the circuit that slow the flow of current. How is the resistance calculated in a series circuit? The total resistance is the SUM of all the resistances of the components. R = = 16Ω What is meant by series circuit? Where current has only ONE way to go around a circuit. What is meant by a parallel circuit? Where current has only TWO or MORE ways to go around a circuit. How is the resistance calculated in a parallel circuit? The current through each device depends on the resistance. The lower the resistance, the bigger the current that will flow through it. If the resistance is high, what happens to the current? It decreases. Why? As electrons are slowed and find it harder to move around the circuit. 6Ω6Ω3Ω3Ω 7Ω7Ω

What circuit is best to be used for Christmas tree lights? Parallel Draw a circuit diagram for this device: Why is this the best circuit to use? As each bulb receives the same voltage. Each bulb with be the same brightness. If a bulb blows, the other bulbs will remain alight. A hair dryer has the following components - 1 motor, 2 bulbs, two heaters and a fan. The hair dryer can work with either 1 heater or both on and the bulbs indicate which heaters are on. Which circuit is best? Parallel Draw a circuit diagram for this device: Why is this the best circuit? As with switch 1 on the motor, bulb and heater are on. When switch 2 is also switched on the second heater and bulb are on. Each component gets the same voltage and can be controlled independently. X X X M X X

What is meant by D.C. and where is it used? Is direct current, where current flows around the circuit in ONE direction only. What is meant by A.C.? This is alternating current where the current is constantly changing direction. How often it is changing direction is shown by the frequency, i.e. 500Hz means it changes direction 500 times per second. How does this a.c. and d.c. look on an oscilloscope? A.C. – constantly changing voltage as current is changing direction. V t d.c. – no change in direction, so no change in voltage: V t What voltage is the UK main supply? 230Volts What frequency is the UK main supply? 50 Hertz What does this mean? The current changes direction 50 times per second. How do you work out the frequency of a wave? Frequency (Hz) = 1. Time period (s)

List some of the ways to reduce electrical hazards in the home: Avoid having long cables Repair frayed cables Do not have electricity near water Do not place metal into plugs/electrical devices. Always have a bulb in a light circuit Draw a inside of a plug and label the wires correctly: Explain why we have 3 pins on our plugs in the UK: As the UK plug have an Earth (the top pin) which is longer, so the appliance is Earthed before the live and neutral are connected. What is the role of the fuse in the plug? Prevents electric shocks. When the current gets too large the fuse wire heats up and the fuse blows so the circuit is broken. The thicker the wire, the more current is can carry before breaking. Why do we have a plastic case to the plug? As plastic is an insulator so that it does not conduct if the cables touch the casing. Therefore, protect you from an electrical shock. Why do some devices need an Earth? If a fault develops in which the live touches the metal case, the electricity goes down the earth wire instead (quicker pathway to earth than through you). This will also blow the sue and prevent electric shock.

What is meant by the Power of an electrical appliance? How long it takes for a device to transform energy. What is the unit of Power? Watts (W) How is Power Calculated? Energy(J) = Power(W) x Time(s) AND Power (W) = Voltage (V) x Current (A) What is meant by total charge through a circuit? How much current flows in a given time. What is the unit of charge? Coulombs (C) How is total charge calculated? Total Charge (C) = Current(A) x Time(s) How is the energy transferred in a circuit calculated? Energy Transferred (J) = Charge (C) x Potential Difference (V) A battery with a larger voltage supplies a larger amount of energy to each electron (charged particle) so more Energy is dissipated in the circuit.