Electricity Flashcards
What is current?
flow of electric charge around a circuit
What is resistance?
anything that slows down the flow in a circuit
How does resistance affect current?
the greater the resistance, the smaller the current
and vice versa
What components have a resistance that doesn’t change with current?
ohmic conductors
eg. wire or resistor
What are ohmic conductors?
Components that has a resistance that doesn’t change with current. At constant temperature, the current is directly proportional to the potential difference.
What does the graph of an ohmic conductor look like?
and why?
a straight line (y=x)
because the current is directly proportional to potential difference
What does the graph of a filament lamp look like?
and why?
curved (s shape)
as current increases, the temperature increases, meaning the resistance increases too
What does the graph of a diode look like?
and why?
curved in positive side of axis
current only flows in one direction in a diode
What is an LDR?
A light dependent resistor is a resistor that is dependent on light.
In bright light, the resistance falls.
In darkness, the resistance increases.
What is a thermistor?
A thermistor is a temperature dependent resistor.
In hot conditions, the resistance drops.
In cold conditions, the resistance goes up.
What can LDRs be used for?
automatic night lights
outdoor lighting
burglar detectors
What can thermistors be used for?
temperature detectors, eg. car engine temperature sensors and electronic thermostats
What are sensing circuits?
circuits that can be used to turn on or increase power depending on the conditions they are in
What is a series circuit?
a circuit where all the components are in one loop
What is the potential difference like across a series circuit?
the potential difference across a circuit adds up (so that the total potential difference of the cells is shared between all the components)
What is current like across a series circuit?
current is the same everywhere
What is the potential difference like across a parallel circuit?
the potential difference is the same across all components in the circuit
What is current like across a parallel circuit?
current is shared between the branches
Describe the mains supply of electricity in the UK
ac supply
230V
50Hz
What are the three types of wire in cables? (and their colours?)
neutral wire (blue) live wire (brown) earth wire (yellow and green stripey)
What is the neutral wire?
blue wire that completes he circuit and carries the current away
around 0V
What is the live wire?
brown wire that provides the alternating potential difference
around 230V
What is the earth wire?
green and yellow wire that is for protection
it stops the appliance casing from becoming live
doesn’t carry a current
What is the national grid?
giant system of cables and transformers that covers the UK, which connects power stations to consumers
How are transformers used in the national grid?
a step up transformer is used to increase the potential difference when its come from a power station and is going to travel across the country
a step down transformer is used to decrease the potential difference before it reaches the consumer so that it is safe
Why does the potential difference need to be high as electricity travels from the power station to consumer?
by increasing the potential difference, the current decreases, which means that less energy will be lost (eg. from heat) meaning that it is more efficent
What causes a build up of static electricity?
friction
Explain static electricty
When some insulating materials are rubbed together, electrons will be transferred from one material to the other, causing the two materials to become charged.
The material gaining the electrons will become negatively charged but the material loosing the electrons will become positively charged.
What happens when there is too much static electricity?
Sparks are created.
As an electric charge builds up on an object, the potential difference between the object and Earth increases. If this gap is large enough, the electrons can jump across the gap -that’s the spark
