Electricity 2 Flashcards
what makes metals such good conductors
they have lots of free electrons that can flow easily
why do insulators not carry electricity
they dont have any free electrons
define ressistance
how hard it is for the electrons to move through a component
what is resistance measured in
ohms
why do high resistance wires get hot
because the electrons are hitting the atoms, transferring energy to them as heat
why does heat a component increase resistance in it
as atoms are vibrating faster, electrons bump into more of them, so its more difficult to get through
power is
the rate energy is transferred by an appliance
power is measure in
watts (W)
power equation
P = E/t (power (W) = energy (J) / time (s))
potential difference =
current X resistance
AC is
alternating current - comes from a generator - potential difference goes above and below 0
DC is
Direct current - comes from batteries and solar panels - potential difference always positive
mains electricity
at 230v and 50Hz
energy transferred =
power (watts) / time (secs)
What is static electricity
when insulators are rubbed against each other (!) electrons rub off one onto the other - creating charge
in static charge
gain of electrons create negative charge
charge is
number of electrons in coulombs - 1 coulomb = 100000000000000000000 electrons!!!!
electrons move very easily through
metals
electric current =
charge (C) / time (s)
current potential difference graphs show
a straight line for constant resistance - gradient = resistance
voltage =
current X resistance
resistors in series circuits
add resistance together
current in series
same through whole circuit
voltage in series
shared between components
current in parallel
all braches add up to current in main branch
voltage in parallel
voltage in each branch same as every other branch
resistance in bulb
goes up as it gets hotter
diode
only lets current through in one direction - if potential difference is negative no current flows
light emitting diode (LED)
gives light if current flows in one direction
becoming commen for of light as give out no heat, so very efficient (cheap!!)
light dependent resistors
as light increases resistance decreases
used in light sensors.
thermistors
as heat increases resistance increases
used in thermostats
variable resistors
dial on them changes resistance
used in dimmer switches
fuses work because
when too high a current goes through they over heat and melt - breaks the current
circuit breakers work because
when too high a current goes through they flick a switch, turning off current - can be turned back on
residual current circuit breakers (RCCBs) work because
they sense difference between live and neutral cable - if too great they switch off - much faster than fuses or circuit breakers
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