electricity key questions Flashcards
what is needed for charge to flow through a closed circuit?
a source of potential difference e.g. a cell
state the units for potential difference
volts (V)
name the component used to measure potential difference
voltmeter
what is a battery?
two or more cells
name three sources of potential difference
cell, battery, power pack
define potential difference
the work done per unit charge
what must a circuit be in order for charge to flow?
closed
how must a voltmeter be connected in a circuit?
in parallel across the component
state the units of current
amps (A)
name the component used to measure current?
ammeter
how must an ammeter be connected in a circuit?
in series
define current
the rate of flow of charge
state the direction of a convectional current
positive to negative
write the equation that links charge current and time
charge= current x time
state the units of charge
coulomb (C)
define resistance
a property of electrical components that opposes the flow of charge
state the units of resistance
ohms (Ω)
state ohm’s law
current is directly proportional to current at a fixed temperature
what is an ohmic conductor
a component that follows ohm’s law
state two examples of an ohmic conductor
wire, fixed resistor
state two examples of non-ohmic conductors
filament bulb, diode
write the equation that links potential difference,current and resistance
potential difference = current x resistance
what is a series circuit?
a circuity where components are in one complete loop
what is a parallel circuit?
a circuit where the components are in more than one loop (branch)
describe how the resistance of a thermistor changes as temperature changes
as the temperature increases, the resistance decreases
describe how the resistance of an LDR changes as light intensity changes
as light intensity increases, resistance decreases
what do we know about current in a series circuit?
it is the same at every point in the circuit
what do we know about potential difference in a series circuit?
the total potential difference of the power supply is shared between the components, and is based on their resistance
describe how we can calculate the total resistance in a series circuit
add them up
what do we know about the potential difference on a parallel circuit?
same as the power supply
what do we know about current in a parallel circuit?
the current splits across branches and re-joins to go back to the power supply
what do we know about the total resistance in a parallel circuit?
it is less than the smallest resistance across a branch
describe how we can find out the resistance of a component during a practical
Use an ammeter in series to measure the current and use a voltmeter in parallel with the component to measure the potential difference. Then use V=IR to calculate the resistance
state the potential difference of mains electricity in the UK
230V
state the frequency of mains electricity in the UK
50Hz
what is meant by direct current (D.C)?
the flow of charge is in one direction only
what is meant by alternating current (A.C)?
the flow of charge is continually changing direction at a specific frequency
what is direct potential difference?
the potential difference is in one direction only
state an example of source of direct current
a battery
state a example of source of alternating current
mains supply
what is alternating potential difference?
the potential difference is continually changing direction
name three wires inside a plug
live (brown), neutral (blue) and earth (green and yellow stripes)
name three safety features in a plug
earth wire, fuse, plasticised pin
define power
the rate of energy transfer
write the equation linking power, current and potential difference
power = current x potential difference
write the equation linking power, current and resistance
power = current2 x resistance
write the equation linking energy, charge and potential difference?
energy transferred = charge flow x potential difference
what is the national grid?
a system of cables and transformers linking power stations to consumers
what does step up transformer do?
they increase the potential difference from the power station to the transmission cables e.g. 400 000V
what does step down transformer do?
they decrease the potential difference for domestic use e.g. 230V
describe why a high potential difference used to transfer electrical power on the national grid?
this creates a low current which reduces energy losses through heating effects, this increases efficiency
