electricity Flashcards
what is electric current
it is the flow of electrons from the NEGATIVE tot he POSITIVE end of a cell
what is current
it is the flow of electrical charge around a circuit and is measures in amperes and can be measures using ammeters
what is the conventional current
it is the idea that electrons flow from the positive end of a cell to the n negative end
how is current distributed in a series circuit
current can never be used up meaning that it will be the same around the whole circuit
how is current distributed in a parallel circuit
the total current of each branch is equal to the total current flowing
what is potential difference
one volt is one joule of energy is transferred for each coulomb of charge
it is the difference in the amount of energy between two points in a circuit
what happens to potential difference in a series circuit
the total potential difference in the circuit is equal to the potential difference of the cell
what happens to the potential difference in a parallel circuit
the voltage across each branch is te same as the cells
what is the charge flow in a circuit
it is measured in coulombs and one ampere is one coulomb flowing per seconds. the size of the current is the rate of flow of electrical charge
what is the formula for charge flow
it is charge flow (coulombs) = current (A) * time (seconds)
what is the formula for energy transferred
energy transferred (J) = charge flow C (coulombs) * potential difference (V)
what is the formula for energy transferred
energy transferred (J) = charge flow (C coulombs) * potential difference (V)
what is resistance
it is the potential difference required to drive a current through an electrical component
or how easily an object resists current
what is the formula for voltage
V = I * R or voltage = current * resistance
what does a current -voltage graph look like for an ohmic component
a directly proportional graph with a straight line
what is an ohmic component
a component that does not change its resistance as you increase the current. However the resistance will only stay constant at a constant temperature
what does the current voltage graph look like for a non ohmic component
it is not directly proportional and gets flatter as the component gets hotter
what does the current voltage graph look like for a non ohmic component
it is not directly proportional and gets flatter as the component gets hotter
why does the resistance increase at high temperatures
at high temperatures the atoms vibrate more causing the electrons in the current to collide more meaning more energy is needed to push the current
what is a diode
a compontent that has very little resistance in the forwards direction but high resistance in the backwards direction
what happens to the resistance in a series circuit
the total resistance is the resistance of all components and resistors added together
what happens to the resistance in a parallel circuit
the total resistance is smaller than the smallest resistor
what does a current to voltage graph look like for a resistor
it is directly proportional
what happens to the resistance of an LDR when light changes
as light increases the resistance decreases and as the light levels decrease the resistance increases
what happens to the resistance of the thermistor as the temperature changes
at low temperatures it has a very high resistance and at high temperatures it has low resistance
how to measure resistance against the length of a wire
use a circuit that measures voltage and current and the use crocodile clips on a piece of wire attached to a ruler to adjust the length
what is the relation of resistance to the length of the wire
they are directly proportional
what is zero error and how can it be accounted for
zero error is a reading on a measuring instrument when the value should be zero and this is a systematic error which cannot be solved by doing repeats. In order to account for this we need to subtract this value from all of our readings.
how can we improve the test to see the affect of altering resistance on a circuit
use a variable resistor or a piece of coiled wire that has a slider that changes its resistance
what is the power rating of an appliance
it is the amount of energy transferred every second
what usually has a higher power rating thermal energy appliances of kinetic
thermal energy
what is the formula for energy
energy (J) = power (W) * time (s)
what is the formula for power
Power (W) = current (A) * voltage (V)
what is the formula for power
Power (W) = current squared (A) * resistance
what is DC voltage
it is the current from a cell that only moves in one direction
what is AC voltage
it is when the current is constantly changing direction
what is the benefit of alternating current
it is very easy to use a transformer to increase or decrease the potential difference
what is the frequency of the main UK electricity
it is 50 hertz or switches direction to complete one cycle 50 times a second
how many volts is the mains UK electricity
around 230 V
what is the function of the live wire
the live wire is the brown wire and carries the alternating potential difference from the supply (230V). The live wire is connected to a fuse in the plug
what is the function of the neutral wire
the neutral wire is the blue one and completes the circuit
what is the function of the earth wire
the green and yellow striped earth wire acts a safety wire to stop the appliance becoming live. If the appliances metal case becomes live electricity flows into the earth wire which is connected to the ground which offsets a huge current to the earth melting the fuse
what is the national grid
it contains high voltage cables and transformers and transfers energy across the UK
what do step up transformers do
they increase the voltage to several thousand volts as less energy is lost when it has a high voltage
