electricity 2 Flashcards
what is a circuit?
something with a closed loop, something for electrons to flow through and a power source
what is current and what’s it measured in?
rate of flow of charged electrons around the circuit
amps (A)
what’s force and what’s it measured in?
the force driving the flow of electrons
voltage
volts (V)
what’s resistance and what is it measured in?
everything that resists or opposes the flow of electrons
ohms (Ω)
which way does a circuit current flow?
positive to negative
which line of a cells are negative and positive?
small line - negative
large line - positive
what is the equation linking voltage, current and resistance?
voltage = current x resistance
what causes resistance to increase?
a high temperature
what’s a diode?
only allows current to flow in one direction
done by using a very high resistance stopping flow from going in other direction
what controls the flow of electricity?
a switch
what’s a fuse?
breaks if too much current
what’s the diode that emits light when current flows through in a forward direction?
light emitting diode
what do ammeters measure?
measure current
where are ammeters placed?
connected in series
what do voltmeters measure?
measure voltage
where are voltmeters placed?
added in parallel
what are the four types of resistors?
variable resistors (modify the amount of resistance)
fixed resistors
light dependant resistors
thermistors
what’s a light dependant resistor?
resistor that depends on light intensity
- in light there is low resistance so lots of current can flow
- in dark there is high resistance so no current can flow
what are some examples of light dependant resistors?
automatic night lights
burglar alarms
what’s thermistors?
dependant on temperature
- higher temperatures cause resistance to fall
- low temperatures cause resistance increase
what’s some uses of thermistors?
car engines
electric thermostats
what’s charge?
charge is a measure of the total current that flowed within a certain period of time
what is charge measured in?
coulombs (C)
what’s the equation for charge?
charge = current x time
does current vary within a series circuit?
no there is the same current everywhere
why is an ammeter placed in series?
as the currents is the same everywhere in a series circuit
how do you calculate the voltage of a single component?
using a voltmeter in parallel to component
what’s a series circuit?
a circuit with one loop
what’s a parallel circuit?
a circuit with more than one loop
what’s the equation to work out energy?
energy transferred = voltage x current x time
how do you work out power?
power = current x voltage
what unit in energy measured in?
joules (J)
what is a surge?
sudden increase in current
what can a surge cause?
a damage in the appliance
fires
electric shocks
what is a fuse and what’s its purpose?
breaks the circuit when the current gets too high
thin wire in the live wire that heats up and melts breaking the circuit so no more current can flow
simple and cheap
permanently broken after a surge
what’s a circuit breaker and what’s its purpose?
breaks the circuit when there is a surge
don’t get permanently damaged
circuit breaks > trip > turn off circuit > can be reset
more expensive than fuses
how can you reduce the harm of surges and live wires?
via earthing
-earth wire (an alternative pathway)
-any electricity is diverted through the earth wire
double insulate
- plastic doesn’t conduct electricity so we can’t get an electric shock
what is static electricity?
build up of charge on insulating materials
can static electricity charge build up on conducting materials?
no as electrons will just transfer back to another
can static charge build-up on insulating materials?
yes
as electrons can’t flow back
when rubbing a cloth and polythene rod together what charges are on both objects?
polythene - negative
cloth - positive
when rubbing a cloth and acetate rod together what charges are on both objects?
acetate rod - positive
cloth - negative
with static electricity, what is the only thing that can be transferred?
electrons
what happens to a balloon when you charge it with friction?
balloon - negative
if you hold ballon to wall electrons are repelled and the balloon is attracted to the positively charged surface of the wall
dangers of electric charge
refuelling:
aircrafts become electrostatically charged during flight (air rubbing against aircraft)
charge can spark to ground or to fuel nozzle
this is very dangerous as it could be near any flammable fuel resulting in an explosion
solution - earth aircraft so charge is discharged to the earth
no build up of charge no risk of spark
dangers of electric charge
lightning:
rising air causes air particles to rub against each other
when change build-up is big enough it will discharge between earth and cloud making a lightning bolt that can cause fires
solution - connect a lightning rod that is earthed reducing risk of fire
uses of electric charge
paint spraying:
nossle has positive charge
object has negative charge
positive droplets repel each other and spread out
advantage - even coat of paint
droplets are attracted to object
no paint wasted
paint sticks to call sides
uses of electric charge
soot removal:
gas particles are negatively charged
negatively charged particles are attracted to the positively charged metal plate
waste gases without particles continue up chimney
metal plates are knocked remove build-up of soot
uses of electric charge
inkjet printer:
ink is negatively charged as it passes through a charger
if top plate is negatively charged the negatively charged ink droplets repel downwards
what’s the structure of metals?
layers of metal ions which are surrounded by delocalised electrons
what’s the hazard of a frayed cable?
plastic insulation is no longer intact causing risk of electric shock
in a short circuit it could cause heating and risk of fire
what’s the risk of long cables?
have larger resistance so wire will heat up and cause a fire
what’s the hazard of damaged plugs?
plastic insulation is missing or broken leaving live wires exposed creating a risk of an electric shock
what’s the hazard water around socket?
water can get into electrical equipment allowing for electricity to conduct to the outside causing an electric shock
what’s the hazard of pushing metal into sockets?
metal is a very good conductor creating risk of electric shock
what is the material and purpose of plug casing?
plastic - hard
insulator so current cannot pass through so no risk of electric shock
what’s the material and purpose of wire covering?
plastic - soft
insulator so current cannot pass through so no risk of electric shock, wires cannot short circuit if encased in same cable
what’s the material and use of prongs?
bass
good conductor so current can easily pass-through
not malleable so will not bend or break
what are wires made out of and why?
copper
very good conductor and cheap
ductile meaning it can be drawn into wires
what colour is the live wire, what’s its charge and its placement in the plug?
brown
right
alternates between +230V to -230V of a.c current
what colour is the neutral wire, what’s its charge and its placement in the plug?
blue
left
always at 0V to complete the circuit
what colour is the earth wire, what’s its charge and its placement in the plug?
green and yellow
middle to the metal casing
there to keep users safe from electric shocks
how do the earth wire and fuse work together?
earth normally doesn’t have current flowing through it
earth wire connected to metal casing of appliance
if live wire touches the metal a big current flows through the live wire and into earth wire which will blow and melt the fuse cutting off live supply
what is dc (direct current)?
when current travels in one direction only
battery supply
portable and low voltage
needs replacing and recharging
positive to negative
what is ac (alternating current)?
when current changes direction continuously
not portable
main supply
high voltage 230V
doesn’t need replacing
why do wires heat up?
wire heats up as the electrons move through wire and collide with the metal ions are vibrating, free electrons will collide with the metal ions transferring energy to the ions in a form of heat
increasing their kinetic energy
what’s a conductor?
something that allows the flow of current
what are good conductors?
all metals , some are better than others
for example :
copper is chosen for household wiring as it is relatively cheap and ductile so can be drawn into wires
aluminium
gold
silver
what are some common examples of insulators?
wood, plastic, glass, air, rubber
what’s the important thing about the casing of the plug?
if casing is not earthed than the appliances casing will be live and LETHAL
what is double insulation?
anything with double insulation just needs a live wire and a neutral wire, no earth wire need
how do you work out power?
power (watts) = voltage (volts) x current (amps)
what are some advantages/disadvantages of series circuits?
- suitable for low power devices
- voltage is shared
- current is the same everywhere
- more components = more resistance = less current
- if one comment breaks the whole circuit is broken
what are some advantages/disadvantages of parallel circuits?
- high powered devices
- current is shared
- splits at a junction
- parallel voltage is the same
- if one component breaks the whole circuit continues functioning
what type of circuit is more appropriate for domestic lighting?
parallel circuit
- if 1 bulb stops working, the others continue to work
- bulbs do not share the brightness, each bulb gets the same amount of voltage supplied by the cell
how does the current in a series circuit depend on the applied voltage and number/ nature of other components?
as voltage increases the current also increases
in general, the more components in a circuit, the lower the current
what’s the relationship of voltage, current and resistance?
voltage = current x resistance
what is current?
rate of flow of charge
what is voltage?
energy transferred per unit charge passed
voltage= current x resistance
what is a volt?
joule per coulomb
voltage= current x resistance
what’s the relationship between energy transferred, charge and voltage?
energy = charge x voltage
changing a metal rod:
remains neutral, hand acts as a earth wire
so small pieces of paper not affected
