P2 ELECTRICITY Flashcards
what can be said about the value of current at any point in a single closed loop?
current is the same at all points in a closed loops
2 factors that current in a circuit depend on?
potential difference
resistance
define electrical current
the rate of flow of electrical charge
define an ohmic conductor?
a conductor where resistance remains constant as the current changes.
name four non-ohmic conductors?
lamps , diodes , thermistor , LDRs
name two ohmic conductors?
wires , fixed , resistors
describe how the resistance of a filament lamp changes with temperature?
as temperature increases , the resistance increases.
ions in metals have more energy , so vibrate more often causing more collisons with electrons as they flow through the metal , creating greater resistance to current flow
describe how a diode conducts electricity
it only conducts electricity in one direction as it has a very high pressure in the backwards direction
describe how the resistance of a thermistor changes with temperature ?
as temperature increases , the resistance decreases.
describe a use of thermistors
thermistors can be used in thermostat circuits to automatically turn the heating on when it gets too cold , or switch it off when its gets hot
describe how the resistance of an LDR changes with light intensity
as light intensity increases , the resistances decreases.
describe a use of LDRs
can be used in automatic lights , to turn on automatically when it gets dark ,and switch off automatically when it gets light
which two things are needed for charge to flow through a circuit
the circuit must be closed and there must be a source of potential difference
state the rule for current in a series circuit?
the current will be the same at all points in a series circuit.
if the resistance of a component increases , what will happen to the current through that component?
it will decrease
unit for potential difference
Volts (V)
units for resistance
Ohms (Ω)
describe how current is measured
with an ammeter connected in series
describe how voltage is measured
with a voltmeter connected in parallel to the component you want to measure
what are the two ways that a component can be connected in a circuit ?
series (same loop)
parallel (adjacent loop)
give the rule for current in series current
the current is the same at all points in a series current
give the rule for current in parallel current
the current in a parallel circuit is shared between the branches of the circuit .
give the rule for resistance in a parallel circuit
when resistors are connected in parallel , the total resistance is less than the resistance of the smallest resistor.
give the rule for resistance in a series circuit
the total resistance in a series circuit is the sum of all the individuals resistances
give the rule for potential difference in a series circuit
potential difference is shared between the components in a series current
give the rule for potential difference in a parallel circuit
potential difference is the same in each branch of a parallel circuit
describe a series circuit
a circuit where all components are connected in one single loops
describe a parallel circuit
a circuit where there are multiple paths and current could take
describe the current in series circuit
the current is the same at all positions since the charge only has one path to flow through
describe the current in series circuit
the current is shared between the different branches . when the charge reaches a junction it splits
why is it advantageous to connect lamp in parallel
if one lamp blows the rest will be unaffected and can still receive current
is mains electricity an a.c supply or d.c supply?
what do these stand for?
mains electricty is an a.c supply
a.c = alternating current
d.c = direct current
what is alternating current?
current that continously changes direction at a specific frequency.
what is direct current?
one directional current flow
what is the frequency and voltage of the UK mains electricity supply?
frequency = 50hz
voltage = 230v
how many wires are usually in the cables connecting electrical appliances to the main?
name these wires
live wire
neutral wire
earth wire
state the insulation colour used on the earth wire
green and yellow
state the insulation colour used on the live wire
brown
state the insulation colour uses on the neutral wire
blue
explain when the earth wire does and doesn’t carry a current
if there is a fault current will flow to the ground.
under normal circumstances no current flows through the earth wire
what potential is the neutral wire at
0 volts
state the potential difference between the live wire and earth wires
230 volts
purpose of neutral wire?
to complete the circuit by connecting main appliances back to the main supply
for metal appliances where is the earth wire connected to?
earth wire is connected to the metal casing of the appliance.
if live wire becomes loose and touches the casing, the current will flow through the earth wire , preventing electrocution
what 2 main factors does the amount of energy transferred by an appliance depend on?
how long the appliance is being used for.
the power of the appliance
describe the energy transfers in a battery powered torch?
The battery converts chemical energy into electrical energy.
bulb converts electrical energy into light as well as waste energy in the form of heating
describe the energy transfer in a battery powered motor?
battery converts chemical energy into electrical energy.
motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction
3 things that determine the power of the circuit?
the p.d across the circuit.
current given through the circuit
amount of energy transferred in a given time
purpose of national grid?
to link power stations to consumers so that they have access to a source of electricity
two types of transformers in national grid?
step up
step down
where are step up transformers found? and what do they do?
used when connecting power stations to transmission cables.
increase potential difference
where are step up transformers found? and what do they do?
used when connecting power stations to transmission cables.
increase potential difference
where are step down transformers found? and what do they do?
used connecting transmission cables to domestic buildings
decrease potential difference
why do transmission lines transfer electricity at high potentials?
high potential , results in a low current
lower the current the less energy is wasted that is wasted as heat
therefore is more efficient
why do transmission lines transfer electricity at high potentials?
high potential , results in a low current
lower the current the less energy is wasted that is wasted as heat
therefore is more efficient
why does the potential need to be decreased between transmission lines and houses
lower potentials are safer for domestic use and reduce the likelihood of severe electrocution
appliances are designed for 230v
