Topic 2: Electricity Flashcards
what is the voltage in a series circuit?
shared amongst components
V(total) = V(1) + V(2) + V(3)
what is the current in a series circuit?
the current is constant in all parts
I(1) = I(2) = I(3)
what is the resistance in a series circuit?
the resistance is the sum of the individual resistances of components
R(total) = R(1) + R(2) + R(3)
what is the voltage in parallel circuits?
all components get the full voltage
V(total) = V(1) + V(2) + V(3)
what is the current in a parallel circuit?
the current is split between branches based on resistance
I(total) = I(1) + I(2) + I(3)
what is the resistance in parallel circuits?
reciprocal of total resistance is the sum of the reciprocals of the individual resistances
how to investigate the current in resistor at constant temperature varied with the potential difference across the resistor
- measure the current using an ammeter
- measure the potential difference using a voltmeter
- vary the resistance of the variable resistor
- record a range of values of current and potential difference
- ensure the current is low to avoid temperature increase
- reverse connect of R to power supply
- repeat measurements of I and V in negative direction
- plot a graph of current against potential difference
in light dependant resistors (LDR) describe the resistance when it is light and dark
- when it is dark - resistance is high
- when it is light - resistance is low
describe what happens in light dependant resistors (LDR) in a circuit when it is dark
- when it’s dark
- high resistance
- low current (stops the current from flowing in)
- so a high potential difference is needed to push the current through
describe what happens in light dependant resistors (LDR) in a circuit when it is light
- when it is light
- low resistance
- high current
- low potential difference
- light bulb will turn off
what is a thermistor dependant on?
temperature - so would be connected to a fan or a boiler
describe the resistance when it is cold and when it hot in a thermistor
- when it is cold you will get high resistance
- when it is hot you will get low resistance
describe what happens in a thermistor in a circuit when it is cold
- when it is cold
- high resistance
- low current
- high potential difference
describe what happens in a thermistor in a circuit when it is hot
- low resistance
- high current
- low potential difference
- will cause the fan to turn on
describe the current in a series circuit and a parallel circuit
series - current is the same everywhere
parallel - current is shared between components
describe the potential difference in a series circuit and a parallel circuit
series - potential difference is shared between components
parallel - potential difference is the same everywhere
describe the resistance in a series circuit and a parallel circuit
series - total resistance = R1 + R2
(adds up)
parallel - resistance is lower than the lowest resistance
what’s an insulator?
does not allow electrical charge to flow - plastics/ rubber
what is a conductor?
allow the flow of charge through the material - metals - delocalised electrons
how to build static charge?
- two insulating materials
- rub the two insulating materials against each other
- this will cause a transfer of electrons
- if the potential difference is large enough - you will get a spark - flow of electrons
positive electric field
- it points outwards
negative electric field
- points inwards
what is the national grid made up of?
step-up transformer
cables/ pylon
step-down transformer
what does the step-up transformer do?
- increases pd
- decreased current
- less resistance
- reduces energy lost as heat
what do the cables/ pylons do?
carry electrical charge and distribute electricity across the country
what does the step-down transformer do?
- decreases pd
- increases current
- makes it safe to use homes and businesses
change of state from solid to liquid
melting
change of state from liquid to gas
vaporisation, evaporation
change of state from solid to gas
sublimation
how to know there’s a change of state on a graph?
- flat part of the graph
why does the temperature not increase when changing the state?
- temperature does not increase
- energy is used to break bonds
- separate particles
increase in temperature
particles are gaining kinetic energy
internal energy is increasing
Describe what the live wire (brown) does
Provides an alternating potential difference (at about 230V) from the mains supply
Describe what the neutral wire (blue) does
Neutral wire completes the circuit - when the appliance is operating normally, current flows through the live and neutral wires.
(It’s around 0V)
Describe what the earth wire (green and yellow) does
- for protecting the wire and for safety
- it stops the appliance casing from becoming live
- it doesn’t usually carry a current - only when there’s a fault
(It’s also at 0V)
Describe what happens to the resistance when temperature increases
The resistance increases
What do we mean by the term conventional current?
Current flows from positive to negative side in a circuit
Describe the graph for a ohmic conductor
- the current through the ohmic conductor (at constant temperature)
- is directly proportional to potential difference, so you get a straight line
Describe the graph for a Filament lamp
- as current increases, the temperature of the filament also increases
- this means less current can flow per unit p.d.
- so the graph gets shallower - hence the curve
Describe the graph for a Diode
- current will only flow through a Diode in one direction
- the Diode has very high resistance in the reverse direction
Describe what happens when certain insulating materials are rubbed together
- when certain insulating materials are rubbed together
- negatively charged electrons will be transferred from one material to another
- this leaves the materials electrically charged
