Electricity Flashcards
what is a cell / battery?
a source of electrical energy and voltage
what does a switch do?
complete or break a circuit
what does a bulb do?
produce light when a current is supplied
how does a bulb produce light?
heating a filament wire
what does a resistor do?
reduce current flow and provides resistance
what is a variable resistor?
a resistor we can vary the resistance of
what does a voltmeter measure?
the voltage / potential difference across a circuit or component
what does an ammeter measure?
the current at a point in a circuit
what is a fuse designed to do?
break / melt under high currents
what does a diode act as?
a one-way switch for a current
what do LEDs do?
convert electrical energy directly into light
what is a LDR?
a resistor whose value depends on light intensity
what is a thermistor?
a resistor that varies with temperature
what is the definition of electric current?
the rat of flow of charge
what is the electric current measured in?
Amperes (A)
what is the electric current equation?
Q=Ixt
what is the definition of voltage?
energy transferred per unit charge
what is voltage measured in?
volts (V)
what is the voltage equation?
V=E/Q
what is the definition of resistance?
the opposition to the flow of current
what is resistance measured in?
ohms
what is resistance affected by?
temperature, cross sectional are, length and material
how does temperature effect resistance?
as temp increases, resistance increases
how does the cross sectional area effect resistance?
as the cross sectional area increases, resistance decreases
how does length affect resistance?
as length increases, resistance increases
what is the ohm’s law equation?
V = I x R
what is ohm’s law?
for a component of fixed resistance, current is directly proportional to the voltage
what are 3 advantages of series circuits?
easier to set up / wire, lower voltage bulbs are required and the battery lasts longer
what are 3 disadvantages of series circuits?
if one component breaks, the whole circuit breaks; each bulb receives less voltage; hard to diagnose individually broken components
what are 3 advantages of parallel circuits?
each bulb receives a greater voltage, circuit won’t break when one component breaks, easy to diagnose broken components
what are 2 disadvantages of parallel circuits?
more complicated to set up, battery doesn’t last as long
what is the definition of power?
the rate of work done / the rate at which energy is transferred
what is the power, work done equation?
power = work done / time
what is the power, energy equation?
power = current x voltage
what is power measured in?
watts
how does the current flow as a direct current?
always the same way
how does the current flow as alternating current?
it constantly changes direction
does convectional current flow positive to negative?
yes
do electrons flow from positive to negative?
no, electrons flow form negative to positive (opposite to current)
what is the frequency of mains electricity and what type of current is it?
50Hz as alternating current
what is the DC equivalent voltage for the mains electricity?
230V
what colour is the live wire and what type of current runs through it?
brown with alternating current
what colour is the neutral wire and what is it set at and why?
blue, it is set at 0V to complete the circuit
what colours is the earth wire and what is it?
green + yellow - a safety feature if the is a fault
what are the 2 main hazards of mains electricity?
electrocution + fires
how does electrocution occur and what is used to prevent this?
happens when contact is made with the live wire - the earth wire and a fuse / circuit breaker can help to prevent this
how do electrical fires occur and what is used to prevent this?
happens when a current that is too high flows through appliances or cables - a fuse or circuit breaker can be used to limit the current to safe levels
true or false? the thinner the fuse wire, the more current is required to cause it to melt?
false, the thicker the fuse wire, the more current is required to cause it to melt
what happens if the casing of a wire / plug becomes live?
the earth wire provides a low resistance path to earth
what is double insulation and what does it do?
it has an outer casing that is made out of plastic - a good insulator - so current cannot flow
what is a circuit breaker?
an electromagnetic device that breaks when the current exceeds a certain value
how does a circuit breaker work?
the electromagnet is always turned on so if there is a current (power) surge, then the electromagnet becomes stronger. the magnetic field produced is strong enough to attract the iron armature so the contacts are pulled apart which breaks the circuit
can circuit breakers be reset?
yes by pressing a button
what is an electrical conductor?
a material that allows electrons to flow through it
what is an electrical insulator?
a material that does not allow electrons to flow through it
what is static charge and where is it most commonly found?
a charge that builds up in one place and is not free to move - most common in insulators
how can static charge be built up?
by friction as it strips electrons off one material and places them on the other meaning one material is positively charged and the other negatively charged
