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GCSE Physics Revision

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tom harris

on 4 January 2013

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Transcript of GCSE Physics Revision

Physics Revision Circuit symbols Ohm's Law Voltage Resistance The Current is directly proportional to the potential difference - provided the temperature is constant All resistors or metallic conductors obey Ohm's Law We often use cells or batteries to move charges around a circuit
They transfer energy into charges
The amount of energy given to the charges by a cell or battery is measured in Volts
A component removes some electrical energy from the charge by transforming it into other forms of energy
Charge (electrons) gains electrical energy when it passes through a cell
Charge losses energy when it passes through a component
The amount of energy that one Coulomb of charge gains or loses is called the Voltage (potential difference) The Voltage across each component tells us how much energy it is converting If we connect a 1.5V cell into a circuit and current flows. 1.5J of energy is given to each coulomb of charge that passes through the cell A joule (j) is the unit of electrical energy We measure voltages using a voltmeter
A voltmeter connected across a component will measure the electrical energy converted into other forms when each coulomb if charge passes through it
A voltmeter connected across a cell or battery will measure the energy given to each coulomb of charge that passes through it Resistors + Variable Resistors A resistor is a component which reduces the current
It transforms electrical energy into heat energy
A variable resistor is just like a fixed resistor but you can also change its resistance using a slider
Variable resistors work by using a coil of resistance wire
if you want a large resistance, then the current passes through a long length of the coil
if you want a small resistance, then the current only passes through a short length of the coil
You can use variable resistors to control the speed of an electrical motor or vary the brightness of a filament lamp All Components offer some resistance to the flow of charge (Current)
Some (Connecting wires) allow charges to pass through very easily losing very little of their energy
Connecting wires have low resistance
The flow of current through some components is not so easy and a significant amount of energy is used to move the charges through them
This energy is converted into other forms (usually heat)
Components like these have high resistance Special Resistors Thermistor - Resistance changes with temperature
Made of semiconducting material (silicone)
Room temp number of free electrons is small = resistance is large
If heated number of free electrons increases = resistance decreases
Used in temp sensitive circuits (fire alarms) LDR's - light dependant resistors contain few free electrons = high resistance
Light is shone onto LDR number of free electrons increases = resistace decreases
LDR's often used for light sensitive circuits (Photographic equiptment, automatic lights) I V R Current = Voltage/Resistance
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