P5
P5 module
- Created by: Laura Godfrey
- Created on: 01-04-10 11:14
Static electricity
Static electricity is created when two objects are rubbed together
objects recieving electons = negatively charged
objects giving up electrons = positively charged
two materials with same charges = repel each other
two materials with different charges = attract each other
Static electricity
Static electricity is created when two objects are rubbed together
objects recieving electons = negatively charged
objects giving up electrons = positively charged
two materials with same charges = repel each other
two materials with different charges = attract each other
Current and Potential difference
Current = flow of charge measured in amperes
Direct current = flows in same direction
Alternating current = constantly changes direction
Metal conductors = lots of charges are free to move
Insulators = no charges free to move
Potential difference = voltage = measured in volts
Adding batteries in series = increases voltage and current
Adding batteries in parallell = potential difference and current stays same and each battry supplies less current
Current and Potential difference
Current = flow of charge measured in amperes
Direct current = flows in same direction
Alternating current = constantly changes direction
Metal conductors = lots of charges are free to move
Insulators = no charges free to move
Potential difference = voltage = measured in volts
Adding batteries in series = increases voltage and current
Adding batteries in parallell = potential difference and current stays same and each battry supplies less current
Resistance
Components = resist flow of charge
Electric current flows through component = component heats up
Greater resistance in a circuit = smaller current
Adding resistors in series = increases total resistance
Adding resistors in parallel = reduces total resistance and increases current through battery.
Current- potential difference graphs = current through resistor is directly proportional to voltage across resistor
Thermistor = resistance depends on temperature
LDR = resistance depends on light intensity
Resistance
Components = resist flow of charge
Electric current flows through component = component heats up
Greater resistance in a circuit = smaller current
Adding resistors in series = increases total resistance
Adding resistors in parallel = reduces total resistance and increases current through battery.
Current- potential difference graphs = current through resistor is directly proportional to voltage across resistor
Thermistor = resistance depends on temperature
LDR = resistance depends on light intensity
Circuits
In series circuits....
- current flowing through each component is the same
- potential difference across components add up to that across the battery
- potential difference is largest across components with greatest resistance
In parallel circuits...
- current flowing through each component depends on resistance
- current running to and from battery is equal to sum of current through each parallel component
- current is smallest across components with greatest resistance
Electromagnetic Induction
When a magnet is moved into a coil of wire, a voltage is induced. If ends of coil are connected a current is induced.
Current can be induced in opposite direction by...
- moving magnet out of coil
- moving other pole of magnet into coil
Electric generators = use electromagnetic induction. produce mains electricity
Generators produce alternating current as the direction of flow is reversed every half turn of the magnet
Transformers = used to change the voltage of an alternating current
Power and energy
Power = measure of the rate of energy transfer
Power (W) = potential difference (V) x current (A)
Energy = measured in joules. Domestic energy is measured in kilowatt hours as joules are very small amounts of energy
Energy transferred (J) (kWh) = Power (W) (kW) x Time (S) (h)
Efficiency = the proportion of energy that is usefully transferred by an applliance
Efficiency (%) = energy usefully transferred / total energy supplied x 100
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