GCSE Physics Help

^{Cell. A cell provides voltage to a circuit. This pushes the charge around the circuit.}

^{Diode. A diode only allows current to flow in one direction. (In the way the triangle points) The diode has a very high resistance in the reverse direction.}

^{A resistor impedes the flow of charge around a circuit. As it does so, it heats up.}

^{LDR. An LDR is a light dependent resistor. Its resistance decreases as the amount of light falling on it increases.}

^{Thermistor. The resistance of a thermoster decreases as the temperature increases.}

^{Ammeter. An ammeter measures the current through part of the circuit. It is always connected in series.}

^{Voltmeter. A voltmeter measures the potential difference between two points. It is always connected in parallel.}

^{Fuse. A fuse melts and breaks a circuit if the current through it is too high.}

^{Variable Resistor. A resistor that's value can easily be changed.}

Ohm's Law

Voltage-Current Graphs

^{For a resistor, the current-voltage graph is a straight line through the origin. The current through a resistor is directly proportional to the potential difference (voltage) across the resistor.}

^{For a filament lamp, as the voltage increases, so does the current. But the increased current raises the temperature of the filament lamp which also increases the resistance. This is why the curve bends toward the end as it is increasingly difficult for more current to flow.}

^{The diode only allows current to flow in one direction. The diode has a high resistance in the opposite direction}

Mr Palmer's AQA GCSE Physics Notes

Current Electricity

Circuit Symbols

Ohm's Law

Voltage-Current Graphs

Components in Series

Components in Parallel

Mr Palmer's AQA GCSE Physics Notes

	Current Electricity Circuit Symbols ^{Switch (open)} ^{Switch (closed)} ^{Cell. A cell provides voltage to a circuit. This pushes the charge around the circuit.} ^Battery ^{Diode. A diode only allows current to flow in one direction. (In the way the triangle points) The diode has a very high resistance in the reverse direction.} ^{A resistor impedes the flow of charge around a circuit. As it does so, it heats up.} ^{LDR. An LDR is a light dependent resistor. Its resistance decreases as the amount of light falling on it increases.} ^{Thermistor. The resistance of a thermoster decreases as the temperature increases.} ^{Ammeter. An ammeter measures the current through part of the circuit. It is always connected in series.} ^{Voltmeter. A voltmeter measures the potential difference between two points. It is always connected in parallel.} ^{Fuse. A fuse melts and breaks a circuit if the current through it is too high.} ^Lamp ^{Variable Resistor. A resistor that's value can easily be changed.} Ohm's Law V : the potential difference across a circuit component measured in volts I : the current through the circuit component measured in amperes R : the resistance of the circuit component measured in ohms The current through a resistor (at a constant temperature) is directly proportional to the potential difference (voltage) across the resistor. The resistance of a component can be found by measuring the current through, and potential difference across, the component. The current though a component depends on its resistance. The greater the resistance the smaller the current for a given potential difference across the component. Example: A FHS girl places a 9 volt battery against her tongue. The shock she feels is from a current of 1.2A. What is the resistance of her tongue? Voltage-Current Graphs Voltage-current graphs show us how the current through a device changes as the voltage is changed. You are expected to be able to identify these three current-voltage graphs and give a basic explanation for their shape. ^{For a resistor, the current-voltage graph is a straight line through the origin. The current through a resistor is directly proportional to the potential difference (voltage) across the resistor.} ^{For a filament lamp, as the voltage increases, so does the current. But the increased current raises the temperature of the filament lamp which also increases the resistance. This is why the curve bends toward the end as it is increasingly difficult for more current to flow.} ^{The diode only allows current to flow in one direction. The diode has a high resistance in the opposite direction} Components in Series The potential difference provided by cells connected in serious is the sum of the potential difference of each cell. (This assumes that the cells are all connected in the same direction. If two cells have the same voltage but are connected in opposite directions, they cancel each other out.) The current in all of the ammeters will be the same as there is only one path in the circuit for the electrons to take. (Electrons mostly don't flow through the voltmeters) The current is the same through each of the components. The voltage across the battery is divided evenly among the circuit components. Each voltmeter will read 3 and one third volts across a resistor. The total resistance of the circuit is equal to the sum of the individual resistances of each component. In this case 5 Ohms + 5 Ohms + 5 Ohms = 15 Ohms for the total resistance The current in the circuit is found by using the voltage supplied by the battery (10V) and the total resistance (15 Ohms) in Ohm's law. Components in Parallel The voltage across the battery is the same as the voltage of each of the components in a parallel circuit. Each voltmeter will read 10 volts. The current that comes out of the battery (in this circuit, 6A) is divided evenly between all the branches of the circuit. Each ammeter after the resistor will read 2A.	Navigation Physics P1 Topics Heat Energy Electricity Power Electromagnetic Spectrum Nuclear Radiation Origins of the Universe Physics P2 Topics Motion Forces Energy Static Electricity Current Electricity Mains Electricity Momentum Nuclear Physics Other Mathematics for Physics