electricity Flashcards
current in a series circuit?
the same everywhere
current in a parallel circuit?
conserved at a junction in a circuit
voltage in a series circuit?
shared between the components
voltage in a parallel circuit?
the same on each branch
what is current?
the rate of flow of charge
equation for charge?
charge = current x time
units for charge equation?
charge - Coulomb (C)
current - Amps (A)
time - Seconds (s)
what is voltage?
the energy difference of a charge between two points
what is the equation to find energy transferred?
energy transferred = charge moved x voltage
what are the units for the energy transferred equation?
energy - Joule (J)
charge - Coulomb (C)
voltage - Volt (V)
current is the flow of ………..
electrons
what does an ammeter measure?
current (in amps)
what does a voltmeter measure?
voltage (in volts)
what is another name for voltage?
potential difference
what is resistance a measure of?
how much a component tries to stop current passing through it
when resistance increases, current ………
decreases
what is variable resistor used for in a circuit?
to vary the current
what is the equation to work out voltage?
voltage = current x resistance
what are the units for the voltage equation?
voltage - Volts (V)
current - Amps (A)
resistance - Ohms (Ω)
as voltage increases, current ……
increases
resistors in series?
when resistors are in series, the total resistance of the circuit is increased because the pathway becomes harder for current to flow through
resistors in parallel?
when resistors are in parallel, the total resistance is less than the resistance of the individual resistors. this is because there are more paths for the current
in order to test or measure the resistance of a component you must have?
- a variable resistor
- ammeter
- voltmeter
- bulb
resistance decreases as light intensity …..
increases
is resistance higher in the dark or light?
the dark
real life examples of light dependant resistors?
- street lamps that turn on and off automatically
- automatic flash settings on a phone
- automatic headlights in car
- security systems
- animal cameras
what is a thermistor?
a resistor whose resistance depends on temperature
resistance decreases as temp ……..
increases
is resistance higher in the hot or cold?
the cold
real life examples of thermistors?
- automatic thermostat
- temp warning lights
- ovens/microwaves
- vehicles - temp warning lights
- digital thermometer
what is a diode?
a component that passes current in one direction but not the other
what is a light dependant resistor?
a component with resistance that increases when the light intensity decreases
what is a thermistor?
a component with resistance that decreases when the temp increases
what causes the wire inside a filament bulb to heat up when electrical charge flows through it?
resistance
what happens if a component is disconnected from a series circuit?
the circuit has been broken so stops working
what happens if a component is disconnected from a parallel circuit?
the current flows down a different path so keeps working
disadvantage of series circuits?
if one stops working, they all stop working
advantage of series circuit?
its simple, because all the bulbs are controlled with one switch
how can a plane become electrically charged while flying?
the electrons are transferred due to friction, leaving a charge on the aircraft
what is a danger of fuelling an electrically-charged aircraft?
a spark
how does connecting the safety wire reduce possible dangers when fuelling an electrically-charged aircraft?
- charge flows through the wire
- it discharged the aircraft by moving the charge to the ground
why are electrical wires wrapped in insulating materials?
to help minimise the risk of electrocution
what is a fuse?
a component which will break if too much current flows through it
what happens if the current in a fuse is too high?
the temp is higher than the wire in the fuse can take and so it melts breaking the circuit, making the device safe
earth wire?
connects to the earth so that excessive charge will conduct and dissipate into the ground
live wire?
connects device to 230V mains electricity. passes through the fuse
neutral wire?
completes the circuit
why are circuit breakers more convenient than fuses?
- a fuse breaks if too much current flows through it, meaning it can only be used once
- circuit breakers detect surges in current
- when a surge is detected, a switch is opened, immediately breaking the circuit
- circuit breakers can be reset by flicking the switch back to its original position
- this makes them more convenient as they can be reused
why are wires made of copper?
it is a good conductor of charge, it allows current to flow
why are wires covered in flexible plastic?
it is a good insulator of charge, prevents electric shock
why is the earth wire longer than the others in a plug?
so the circuit can’t be used without an earth wire
which direction do charges move in direct current?
all charges move in one direction around the circuit, so voltage is either positive or negative
what provides the charge in a direct current?
batteries and cells
which direction do charges move in alternating current?
charges constantly change direction (back and forth), so voltage goes between being positive and negative
what provides the charge in an alternating current?
mains power supplies
how does heating happen in electric circuits?
- a resistor contains an ion lattice
- when electrons collide with the ionic lattice they transfer energy to heat
- this is the heat that dissipates into the surroundings
advantage of heating effect in electric circuits?
some components want to heat, like electric heaters
disadvantage of heating effect in electric circuits?
- wasted heat energy costs money and resources
- if some components get too hot, they can stop working or catch fire
what is the relationship between energy, voltage and charge
energy = charge x voltage
what is the relationship between power, energy and time?
power = energy/time
energy transferred equation?
energy transferred = current x time x voltage
relationship between power, current and voltage?
power = current x voltage
what type of current is mains electricity
alternating current (a.c.)
what type of current is being supplied by a cell or battery
direct current (d.c.)
what happens to the current if the voltage increases
the current increases
what happens to the current if you increase the resistance
less current will flow
current in diodes
current can only flow through in one direction
what can lamps and LEDs be used to do
indicate the presence of a current in a circuit
what is electric current in solid metallic conductors
a flow of negatively charged electrons
everyday materials that are electrical conductors
copper, brass, steel, gold, aluminium
everyday materials that are electrical insulators
rubber, plastic glass, wood
practical: investigate how insulating materials can be charged by friction
1) POLYTHENE AND ACETATE RODS
- rub polythene and acetate rods with a cloth duster
- when polythene rod is rubbed with duster, electrons move from duster to rod -> rod becomes negatively charged
- when acetate rod is rubbed with duster, electrons move from rod to duster -> rod becomes positively charged
how are positive and negative electrostatic charges produced on materials
- electrons are negatively charged
-> when a material loses electrons, it loses that negative charge and becomes positively changed
-> when a material gains electrons, it gains that negative charge and becomes negatively charged
forces of attraction between…
opposite charges
forces of repulsion between….
alike charges
uses of electrostatic charges
1) INKJET PRINTER
- tiny droplets of ink are forced out a fine nozzle, making them charged
- droplets are deflected as they pass between two metal plates
-> voltage is applied to the plates - one is negative one is positive
- droplets are attracted to plate with different charge and repelled from plate with same charge
-size and direction of voltage across each plate changes so each droplet is deflected to hit a different place on the paper
2) PHOTOCOPIER
- image plate is positively charged
- lighter bits of what your photocopying make light fall onto plate and charge leaks away in those places
- charged bits attract negatively charged black powder
- paper is heated so powder sticks
