Please enable JavaScript.
Coggle requires JavaScript to display documents.
Physics: Unit 2: electricity. - Coggle Diagram
Physics: Unit 2: electricity.
required practical: factors affecting the resistance of an electrical component.
how the lengh affects the resistance of a wire.
set up the standard est circuit as shown.
pretest the circuit and adjust the supply voltage to ensure that there is a measurable distance in reading taken at the shortest and longest lengths.
record the voltage and current at a range of lengths using crocodile clips.
use the variable resistor to keep the current through the wire the same at each length.
use the voltage and current measurements to calculate the resistance.
independant variable: lengh of wire.
dependant variable: voltage/potential difference.
control variable: current.
charge flow = current x time or Q=IT
components.
resistors: ohmic conductor is a resistor in which current is directly proportional to the potential difference at a constant temperature - means that the resistance remians constant as the current changes. - linear graph.
filament lamps - as temp increases so does current through the filament lamp. causes the resistance to increases as the current increases - curved graph.
diodes - current through a diode will only flow in one direction so it has very high resistance in the reverse directon. indicated by a horizontal line in x axis showing no current flowing. exponential graph
thermisters: resistance of thermistor decreases as temperature increases. useful in circuts where temp control is required. e.g used in thermostats to turn the heater at a particular temperature.
light dependant resistors LDR - resistance decreases as light intensity increases. useful where automatic light control is needed. e.g street lamps
series and parallel circuts.
series - same current through each component. the total potential difference of power supply is shared between components. the total resistance of two components is the sum of the resistance of each component. as current travels through each component in turn.
parallel - potential differences across each component are the same. the total current dram from the power supply is the sum of the currents through the separate components. the total resistance of two resistors is the tan the resistance of the smallest individual resistor because in parallel there are more paths for the current to take which makes it flow more easily.
power = potential difference x current. or P=IV Power = current squared x resistance P=i2r
mains electricity
230V 50Hz (changes direction 50 times a seond)
live wire - brown - carries current to the appliance, 230v
neutral wire - blue - carries current away from the appliance, 0v
earth wire - green and yellow striped - protect from electric shock.
what happens: potential difference causes current to flow through the live and neutral wires. the live wire carries the alternating potential from the supply. the neutral wire completes the circuit. current only flow in earth wire if there is a fault connecting it to a zero potential
power: the rate at which energy is transferred or work is done. power = work done / time or power = energy transferred / time. 1J a second is equal to 1W of power.
efficiency - the ration of useful energy out to total energy in. efficiency = useful power output / total power input
energy transfer in appliances
whenever a charge flows it has to overcome the resitance of the circut. energy required. therefore: - work is done when charge flows. - amount of work done depends on the amount of charge that flows and the potential difference.
energy transfered = power x time E=PT ㅤㅤㅤㅤㅤㅤㅤㅤenergy transfered = charge flow x potential difference E=QV
the national grid.
system of cables and transformers linking power stations to homes and businesses. power station 25,000v -> step up transformer -> transmission cables 400,000V -> step down transformer -> houses shops ect 230v
power station: energy supply into electrical supply. larger smaller amount of power stations used as they use steam turbines which are more efficient at higher temperatures, bigger the plant the bigger the boiler so higher the steam temperature.
step up transformers - increase the potential difference from power station to transmission cables. reduces current and therefore reduces the heating effect caused by the current flowing in the transmission cables. reducing heating reduces energy loss and makes it more efficient.
static charge
when insulating materials are rubbed together they can become electrically charged. friction moves negatively charged electrons from one material to another. - the object that gains electrons becomes negatively charged and object that looses electrons becomes positively charged,
direct current
potential difference that is always positive or always negative. the current direction is constant. type of current that is supplied by cells and batteries.
alternating current
potential difference that alternates from positive to negative. the current direction changes. is the type of current used in mains electricity.
required practical
set up the standard test circut as shown. 2. use the varible resistor to adjust the potential difference across the test component. 3. measure the voltage and current fr a ramhe of voltage values. 4. repeat the experiment at least three times to be able to calculate the mean. 5. repeat for the other components to be tested.
independant variable: potential difference across the component.
dependant variable: current through the component measured by the ammeter.