electricity and circuits - topic 9 Flashcards
charge of neutrons
neutral
charge of protons
+1
charge of electrons
-1
is current shared or same in series circuit
same
is voltage shared or same in series circuit
shared
is current shared or same in a parallel circuit
shared
is voltage shared or same in a parallel circuit
same
difference between series and parallel circuit
In series, current only flows in 1 direction, components are all dependant on each other and they are all connected in 1 line
are voltmeters connected in parallel or series
parallel with a component to measure the voltage across it
are ammeters connected in parallel or series
in series with a component to measure the current in the component
what is electric current
the rate of flow of charge
what is current measure by and in
current is measure by an ammeter in amps
what is the conservation of current
current leaving positive terminal is the same amount as it is when it re enters through the negative terminal
what is charge measured in
coulombs
what is voltage
the energy transferred per coulomb of charge or the force required to push the electrons around the circuit
what is voltage measure by and in
voltage is measure by a voltmeter in volts
what is resistance
the opposition to the rate of flow of charge
what is resistance measure in
ohms
what causes a filament lamp to light and heat up
a potential difference across the filament lamp causes a current to flow through which cause it to light up and heat up.
why do diodes have very high resistance in one direction of circuit
to prevent the current from moving backwards
what is power
the amount of energy transferred every second
what is power measured in
watts
what is AC
alternating current is the forward and backward movement of charge
what is DC
direct current is the movement of charge in only 1 directions
what is the brown wire
the live wire
what is the green and yellow wire
the safety wire
what is the blue wire
the neutral wire
what is a fuse
a fuse is a safety feature which will overheat and melt and therefore break the circuit, if current surpasses the amount and is too high
what is a circuit breaker
a safety feature which will break the circuit if it detects changes in current
difference between circuit breaker and fuse
circuit breaker don’t have to be replaced unlike fuses
equation for power(1)
power = current^2 x resistance
equation for energy (1)
energy = current x time x voltage
equation for power (2)
power = current x voltage
equation for energy (2)
energy = power x time
equation for charge
charge = current x time
equation for energy (3)
energy = charge x voltage
equation for voltage
voltage = current x resistance
what is current in metals
a flow of electrons
what happens when there is an electric current in a resistor
there is an energy transfer which heats the resistor
what happens to electrical energy when an electric current does work against electrical resistance
electrical energy is dissipated as thermal energy in the surroundings
why is electrical energy dissipated as thermal energy in the surroundings
free electrons collide with the ions that make up the lattice. These collisions transfer energy from the electrons to the ions, making the ions vibrate and causing the resistor to heat up
how does the resistance of a thermistor vary with change if temperature
in hot conditions, resistance drops
in cool conditions, resistance goes up
how does the resistance of an LDR vary with light intensity
in bright light, resistance falls
in darkness, resistance is highest
how do you investigate the resistance of thermistors
place the thermistor in a water bath and pour enough water in to cover the thermistor
turn on the water bath
measure and record the temperature of the water using a thermometer
measure the current through the circuit for every 5 degree increase in temp
the potential difference needs to be kept constant throughout
use the pd of the power supply and values of current recorded to calculate resistance of the thermistor at each temp
you should find as temp increases, resistance decreases
how do you investigate the resistance of LDR’s
in a darkened room, use a torch to shine a light on the LDR
record the distance between the torch and LDR
gradually move the torch away from the LDR so the intensity of the light hitting the LDR will decrease
recocrd the current through the LDR every 10cm you move the torch
use resistance = voltage/current to calculate resistance of the LDR for different light intensities
you should find as the torch moves away, resistance increases
what does an I-V graph look like for a fixed resistor
you get a straight line , because the current through a fixed resistor is directly proportional to voltage
what does an I-V graph look like for filament lamps
you get a curve because resistance increases with temperature so as more current flows through the lamp, the lamp heats up more and resistance increases. This means less current can flow per unit potential difference, so graph gets shallower
what does an I-V graph look like for thermistors
a curve, because as a current flows through the thermistor the thermistor heats up. this causes the resistance of thermistor to decrease so the graph becomes steeper
what does an I-V graph look like for LDR’s
straight line, because the resistance of an LDR only depends on light intensity
how are series circuits connected
the different components are connected in a line end to end between the positive and negative ends of the power supply except the voltmeter
what happens if one component is removed or disconnected in a series circuit
the circuit is broken and they all components stop
why are series circuits built and designed in this way
to test and measure components
total circuit potential difference in a series circuit =
voltage across component 1 + voltage across component 2 + …….
total current flowing in a series circuit =
current through component 1 = current through component 2 = ……
total resistance in a series circuit =
resistance of component + resistance of component 2 + ..
source potential difference in parallel circuits =
pd across component 1 = pd across component 2 = …..
total current flowing in parallel circuits =
current through branch 1 + current through branch 2 + ….
if two resistors are in parallel, why is the net resistance decreased
by adding another additional loop, the current has more than one direction to go in which increases the total current that can flow around the circuit and using V =IR an increase in current means a decrease in total resistance
what are the differences between series and parallel circuits
current through all components in series is the same, in parallel it depends on the resistance of each component
the total pd is shared across components in series and depends on its resistance
the total resistance of components in series is the sum of all the components resistances, but total resistance in parallel decreases as more components are added
how do you investigate resistors in circuits
construct a circuit with a resistor, ammeter and a battery
measure the. current through the circuit with the ammeter
use current and pd of the battery to calculate resistance
use R = V/I
add another resistor in series or parallel
measure the current through the circuit and use the pd of the battery to calculate overall resistance
repeat until you have added all your resistors
plot a graph of number of resistors against total resistance
how is energy transferred from different domestic devices
kettles transfer energy electrically from the mains a.c. supply to the thermal energy store of the heating element inside the kettle
how can you reduce unwanted energy transfer
by using low resistance wires, as less energy will be transferred to the thermal energy stores
what are the advantages of the heating effect of an electric current
fuses will melt and break the circuit if the current gets too high which prevents fires and electrical shocks
what are the disadvantages of the heating effects of an electrical current
it reduces the efficiency of a process as less energy is transferred to useful energy stores
it can cause components in a circuit to melt, so circuits won’t work properly
what is power
energy transferred per second
what is power measured in
watts
what is the relationship between power ratings for domestic electrical appliances and the changes in stored energy when they are in use
the lower the power rating, the less electricity an appliance uses in a given time, so the cheaper it is to run
what does the power rating tell you
the maximum amount of energy transferred between stores per second when the appliance is in use
how is power transfer related to the pd across it and the current in it
the higher the voltage or current, the more powerful the appliance
what is the movement of charge like in a.c.
the charges are constantly changing direction
is the domestic supply in the UK a.c. or d.c.
alternating current
what is the frequency of the UK domestic main supply
50Hz
what is the voltage of the UK domestic main supply
230V
what is direct current
the movement of charge in one direction only
do cells and batteries supply a.c. or d.c.
direct current
what is the difference between direct and alternating voltage
direct voltage is when the positive and negative ends of the source are fixed
what is the difference in function between the live and neutral mains input wires
the live wire provides electricity form the main supply and current flows in through the live wire
the neutral wire carries away current
what is the pd between the live, neutral and earth mains wires
pd between live and neutral wire is 230V
pd between live and earth wire is 230 V
pd between neutral and earth wire is 0V
what is the danger of providing any connection between live wire and earth
if the link creates a low resistance path to the earth, a huge current will flow, which would result in a fire
why should switches and fuses be connected in the live wire of a domestic circuit
if there was a problem, the supply of electricity to the appliance can be cut off
what is the function of fuses in ensuring safety
if the current increases beyond a certain point, the wire gets too hot and melts. The fuse blows and the circuit is broken and electricity cannot flow
what is the function of earth wires in ensuring safety
earth wire is connected to the metal casing, which provides a low resistance path for a current to travel down in the event of a fault and as the resistance is low, a large current flows, causing a current surge which metls the fuse
what is the function of circuit breakers in ensuring safety
a large current will trip a circuit breaker quicker than it takes a fuse to melt and they can be reset instead of replaced
