P2 Flashcards
need to be done: graphs and equations, parallel and series circuits, LDR thermistor diodes
what is voltmeter
- measures potential difference
- must ALWAYS be placed in parallel
what is an ammeter
- measures current
- must ALWAYS be placed in series
what happens to the current in series circuits?
the current through all the components is the same
what happens to the potential difference in a series circuit?
it is shared between the components
what happens to the resistance in a series circuit?
- the total resistance of two components is the sum of the
resistance of each component.
-the resistance increases as more components are added
what happens to the current in a parallel circuit?
the total current through the whole circuit is the sum of the
currents through the separate components
what happens to the potential difference in a parallel circuit?
the pd across each component is the same
what happens to the resistance in a parallel circuit?
the total resistance of two resistors is less than the resistance
of the smallest individual resistor.
what is an LDR dependent on?
light intenisty
how does light intensity affect the resistance in an LDR?
the resistance of an LDR decreases as light intensity increases
what happens to the resistance if an LDR in bright light?
the resistance falls
what happens to the resistance of a LDR in darkness?
the resistance is the highest
what does the resistance of a thermistor depend on?
temperature
what happens to the resistance of a thermistor in hot conditions?
the resistance drops
what happens to the resistance of a thermistor in cool conditions?
the resistance goes up
how does the temperature affect the resistance of a thermistor?
the resistance of a thermistor decreases as the temperature increases
how does a current in a diode flow?
in only one direction
what happens to the resistance of a diode in the reverse direction?
it’s very high
describe the relationship between current, temperature and resistance in a filament lamp.
as current increase, the temp of the filament increases —> this means less current can flow per unit p.d, so the graph gets shallower, hence the curve
describe the relationship between the current and potential difference in an ohmic conductor.
it is directly proportional.
- this means that resistance remains constant as the current changes
what is the blue wire known as?
the neutral wire
what is the p.d of the blue wire?
0V
what 2 things does the neutral wire do?
- carries current away from the appliance
- completes the circuit
what is the p.d of the earth wire?
0 Volts
- unless there is a fault
what is the brown wire known as?
the live wire
what is the p.d of the brown wire?
230V
what does the live wire do?
carries current from the main
- can kill you
what is the green and yellow wire known as?
the earth wire aka the safety wire
what is the function of the cable grip?
holds wires securely
what are the cable grips made of? why?
plastic bcus it’s a good insulator
what is the function of the fuse?
- prevents electric shock
- protects appliances
what does the fuse contain?
thin wire that melts if the current is too large
what is the fuse rating normally?
is normally higher than what the device requires
what material is used for the pins/ connectors?
Brass
- allows current to flow
-strong and good conductor
Direct current
flows in 1 direction
- meaning p.d stays constant
what supplies DC?
batteries
what is the UK’s main electricity supply? what is the voltage and frequency?
Alternating Current (AC)
Voltage = 230 V
Frequency = 50Hz
Alternating current?
constantly changes direction
- the pd also changes so switches between +ve and -ve
what does a step up transformer do?
increase the p.d and decreases the current
what does a step down transformer do?
decreases p.d and increases current
what are the steps for electricity leaving power station to your house?
- leaves the power station (25,000V)
- enters step up transformer
- enters power cable (400,000V) to be distributes across the country
- then passes through the step down transformer
5 finally enters home (230V)
what are 3 advantages of underground cables?
- doesn’t cause visual pollution
- aren’t damaged due to bad weather
- don’t cause problems for aeroplanes
what are 2 disadvantages for underground cables?
- expensive
- hard to repair
what are 2 advantages of overhead cables?
1.cheap
2.easier to fix
what are 3 disadvantages of overhead cables?
- visual pollution
- damaged in bad weather
- cause problems for aeroplanes
what is electric current?
the rate of flow of electric charge
what is potential difference?
a measure of electric work done for every coloumb of charge that flows through a component
PRACTICAL: resistance in a wire
- set up circuit as shown in the diagram
- connect a lead from the negative side of the ammeter to the crocodile clip at the 0cm end of the ruler
- attach the other crocodile clip to the wire at the 30 cm end
- ensure the power pack is set no higher than 3V to minimise overheating the wire
- turn on the power pack
- record the current and voltage
- turn off the power pack in between readings
- repeat steps 3-7 moving the crocodile clip to 40, 50, 60, 70, 80, 90 and 100cm
- repeat whole experiment 2 more times
- calculate and record the resistance for each length of the wire: resistance = p.d/current
what is the unit for energy?
Joules (J)
what is the unit for charge?
Coulombs (C)
what is the symbol for charge?
Q
what is the unit for pd?
Volts (V)
what is the unit for power?
Watts (W)
What is the unit for time?
Seconds (s)
what is the unit for current?
Amps (A)
what is the symbol for current?
I
what is the units for resistance?
Ohms
