physics paper 1 electricity Flashcards
what is work done
work done id the flow of electrons which allows energy to be transferred
why does current transfer energy to resistors
electrical current flow through metal conductor, when it flows through a component the electrons collide with atoms within it and transfer their electrical energy into other forms.
resistance tells us the potential difference/ voltage ( energy ) required to drive a current through a component.
the higher the resistance, the more energy transferred
current and potential difference are directly proportional (potential difference is the amount of energy transferred)
an ohmic conductor is a component that obeys ohms law which is that resistance does not change (stays constant) even if current changes.
diodes only allow the current through in one direction, this is because they have a very high resistance in the other direction.
the current cannot flow in a revere direction which is shown in the graph
diodes are very good for controlling the current in a circuit.
as current in forward direction increases so does potential difference
feature of LED
LED are very energy efficient and give off light as a current is passed through
what is the resistance in parallel
the total resistance in parallel is less that the resistance of the smallest individual resistor
effect wire length has on resistance
secure a wire to a metre ruler using sellotape. Then adjust the circuit to the wire using crocodile clips at a certain length. next repeat with different lengths.
wire length and resistance are directly proportional
problems with experiment:
systematic error/ zero error - crocodile clip cannot be placed exactly on the zero.
resistance caused by the contact between the wire and the clips
if the heat increases of the wire the resistance increases which affect the results.
solutions- use a low potential difference with keeps the current low reducing the heating of the wire
turn on the Current when taking a reading turn off the current between readings which will reduce heating effects
what are the uses of a thermistor
thermostats are appliances that regulate temperature. their resistance increases when temps are to low and resistance increase when temps are too high
how is a thermistor effective In controlling the heat of a computer
a computer has a built in fan with a thermostat, when the temp gets too hot the resistance of the thermistor decreases . as a result there is more potential difference for the fan to use so it can spin at a faster rate producing more air to cool it down. when the temp gets lower the resistance of thermostat increases there for there is less pd for the fan and the fan operates at a lower pd producing not much air
in an incubator it
how are light dependant resistors useful in phones
light dependant resistors can be used to detect light. If light intensity is low than resistance increases, if light intensity is higher resistance decreases
LDR resistance and potential difference is directly proportional if temperature is constant.
when the phone is near your ear there is less light there for increased resistance.There will be less electrical energy for the lamp as there is more pd to the resistor, as a result light will become dimmer.
when the phone is away for ear there is more light, resistance increase and there is more electrical energy for lamp. pd across lamp increases and the phone in light becomes brighter.
what is an ohm conductor
material that obeys ohms law meaning the resistance stays the same regardless of the p.d/ voltage and current passing through it.
describe the wire and resistance practical
sellotape a wire onto a rule. than using crocodile clips adjust the circuit to the wire at a certain length and then different lengths.
the longer the wire the higher the resistance/ wire and resistance are directly proportional.
errors with the experiment - zero systematic error- the crocodile clip creates a slight resistance even when length of the wire is zero. there for we will have to subtract the zero error from all reading.
if the temperature of the wire increase than the resistance can increase which will lead to inaccurate results, there for they should use a lower pd which will reduce current to reduce thermal energy heating unwire. or turn off the current in-between reading to avoid heating up.
why is a variable resistor useful
variable resists is useful as its resistance and can increase and decrease with will control the potential difference across the other component. as length of wire increases resistance increase there for variable resistors decrease and increase with diff lengths.
what is the practicals for a resistor, filament lamp and diode.
resistor- in a series circuit include a battery, resistor, variable resistor, ammeter and voltmeter. include the initial readings on the volt and ammeter and plot on a graph. then repeat adjusting the resistance on variable resistor and record the results. reverse the direction of the battery and plot results again. you will find that the resistor is an ohmic conductor as the potential difference and current will be directly proportional, if the temp remains constant is do not leave circuit connected for too Long
do this with the fitment lamp yet you wont get directly proportion
repeat with diode however use a resistor as diode is easily damaged by current and resistor will reduce the current through the diode, however will have to use a millimetre as the current will be very small and then plot results on graph. Repeat in opposite direction however line will be flat as current can flow in reverse direction through diode as it has a very high resistance in the reverse direction.
what is power
power is the rate at which energy Is transferred measures in watts
why would it mean if an appliance was 200 watts
it would mean it transfers 200 joules of energy every second
