Physics Unit 2 Revision (Higher tier)

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(c)Explain, in terms of electron movement, what happened as the rodswere rubbed with the cloths....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................Current and circuitsWe use symbols in circuits and you need to be able to recognise and drawcircuits using the following symbols.(3)(Total 8 marks)OpenSwitchClosedSwitchLampCellDiodeThermistorBatteryVoltmeter(connect inparallel)Resistor Fuse VariableresistorAmmeter(connect inseries)Light dependent resistor (LDR)Light emitting diode (LED)A diode is a component thatonly allows current to flowone way in a circuitThis is a temperature resistor. Asthe temperature increases theresistance decreasesA LDR is a resistor whoseresistance decreases if thelight intensity increases(more light shining on it)This is a resistor whore resistancecan be changed. E.g. a dimmerswitchA light emitting diode (LED) is a component that only allows current to flowone way in a circuit and when the current is flowing that way it gives off light
Current (symbol I, measured in amperes, A) is the rate of flow of electricalcharges (symbol Q) or electrons i.e. The number of charges per second.Current is the amount of charges (measured in Coulombs) thatflow every second, it is represented by the equation:Charge, QCurrent (Ampere, A) = Charge (Coulombs, C) ÷ Time (s)Current, ITime, tSo if a circuit has a current of 2A that means that there are 2 coulombs ofcharge going around the circuit every secondQuick example: 6 Coulombs of charge go around a circuit every 2 seconds.What is the current?Answer: I = Q ÷ tI = 6C ÷ 2s = 3AVoltage or potential difference (symbol V, measured in volts, v) is theamount of energy transferred by the charges i.e. the amount of energy perchargeIf there is a 2V cell or battery in a circuitthen it gives 2 joules of energy to everycoulomb of charge. When these charges get tothe device in the circuit e.g. a bulb, then theenergy gets transferred to the device. Tocalculated potential difference/voltage you usethe following equation.Work done ( J)Potential difference ( V ) Charge ( C)Resistance (symbol R, measured in ohms, Ω) is something that apposes theflow of current.Voltage, current and resistance related bythe equation:V = I x RIVR
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Physics Unit 2 Revision (Higher tier)

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