P2/Electricity Flashcards
describe resistance in a thermistor?
as temperature increases resistance decreases
where might a thermistor be used?
central heating system
oven
describe resistance in an LDR?
as light intensity increases resistance decreases
where might an LDR be used?
security lighting
describe current in a series circuit
it is the same current all the way round
describe potential difference in a series circuit
the total potential difference of the power supply is shared between the components
describe total resistance in a series circuit
the total resistance of the two components is the sum of the resistance of each component
what is the unit for resistance?
Ohm
what is the unit for potential difference?
volts
what is the unit for current?
amps
describe current in a parallel circuit
the total current through the whole circuit is the sum of the currents through the separate components
describe potential difference in a parallel circuit
it is the same across each component
describe total resistance in a parallel circuit
the total resistance of two resistors is less than the resistance of the separate components
what is the frequency of the UK mains supply?
50 Hertz
what is the potential difference of the UK mains supply?
230 volts
mains electricity is an a.c supply.
what does this mean?
current constant;y changes direction
what does d.c mean?
current flows in only one direction
what is needed for electrical charge to flow?
a potential difference
what is electric current?
a flow of charge
what determines the size of an electrical current?
the rate of flow of electrical charge
describe the current in a series circuit
it is the same all the way around
what does current through a component depend upon?
the resistance of the component and the potential difference across it
how does resistance affect current?
the higher the resistance the lower the current
describe the current through an ohmic conductor
current is directly proportional to the potential difference
describe the resistance of an ohmic conductor
resistance remains constant
describe the resistance of a filament lamp
the resistance of a filament lamp increases as the temperature of the filament increases
describe current flow through a diode
current flows in one direction
describe resistance of a diode
very high resistance in one direction
what colour is the live wire?
brown
what colour is the neutral wire?
blue
what colour is the earth wire?
green and yellow stripes
what is the function of the live wire?
it carries the alternating potential difference
what is the function of the neutral wire?
completes the circuit
what is the function of the earth wire?
it is a safety wire to stop the appliance becoming live
what is the potential difference between the live wire and the earth?
230v
when would the earth wire carry a current?
only if there is a fault with the appliance
how do electric shocks occur?
when a person makes a connection between the live wire (230v) and the earth (0v)
what is the unit for power?
watt
what determines the energy an appliance transfers?
its power rating and the length of time it is switched on for
in an electrical circuit- work is done when…
charge flows in a circuit
what is the national grid?
a system of cables and transformers linking power station to the cables
what do step up transformers do?
increase potential difference from the power station to the cables
what do step down transformers do?
decrease potential difference
why do we use transformers in the national grid?
to reduce energy loss during transmission by using a high potential difference and low current
how do objects become charged?
by rubbing two insulators together
why do objects become charged?
because they gain or lose electrons
what is the charge of a material that gains electrons?
negative
what is the charge of a material that loses electrons
positive
two objects that carry the same charge will ……. each other
repel
two objects that carry opposite charge will ……. each other
attract
is electrostatic force a contact or non-contact force?
non-contact
what can be found around a charged object?
an electric field
where is the field strongest?
nearest the charged object
