Unit 2 - Electricity Flashcards
disadvantages of nuclear power plants
- radioactive waste is produced, which is difficult to dispose of safely.
- It’s expensive to set up and close down nuclear power stations.
- There is a risk of radiation leaks and catastrophes.
define current
rate of flow of charge
what carries charge
electrons
other names for voltage
emf (electromotive force)
potential difference
from which terminal does current flow
positive to negative
define voltage
the amount of energy needed to transfer one coulomb of charge between 2 points
define direct current
a current with the same current and direction
define alternating current
a current with changing magnitude and direction
define resistance
A measure of how hard it is for current to flow through a material or component
what is a live wire
Wire in a circuit with a high voltage compared to the other wires
what is a neutral wire
Wire that completes the circuit; the voltage is always compared to this wire
what is an earth wire
Wire in a circuit that prevents electrical shock. These are only needed in devices with metal cases.
what are insulators
Materials that do not allow a current to flow, they do not contain free moving electrons .
for example plastic or rubber
what is double insulation
A protection method which avoids the need for an earth wire. Two layers of insulating material, usually rubber and plastic, are used.
what is power
energy transferred per second
what is a diode
a diode only allows current to pass in one direction.
( This means that if the voltage is positive, the resistance is very low and the line is very steep. If the voltage is reversed, the resistance is so high that no current flows at all.
thermistor function
As temperature decrease resistance increase
light dependent resistor function
examples of direct current
batteries and solar cells
which appliances make use of induction
generators
describe how an earth wire acts as a safety feature [4]
- the earth wire is fitted to the metal casing of the appliance , providing a low resistance path to the earth
- this means that if there is an excess current in the appliance due to a fault , the current passes into the earth wire
- the large current in the earth wire causes the fuse to melt
- this breaks the circuit and stops the flow of current
explain how a fuse works
when a current greater than the value of the fuse flows through the circuit , the fuse melts this breaks the circuit so no further current can flow. This prevents the current from overheating
advantages of using a circuit breaker over a fuse
- a circuit breaker an be reset while a fuse needs to be replaced after it has melted
- circuit breaker works instantly, while a fuse needs time to heat up enough to melt
- circuit breaker are more sensitive than fuses
- a circuit using a circuit breaker doesn’t not require an earth wire, whereas one with fuse does
common question - justify your fuse rating choice
answer is the closest value above the current required
Suggest reasons why nuclear fission models are usually tested before setting up a nuclear power plant
- to make sure the fusion process is possible
- to develop an understanding of the process
- to make predictions
- assess safety risks
how to charge a conducting sphere by induction
(1) bring the charged rod close to the sphere
(2) connect the earthing
(3) remove the earthing remove the rod
what happens to the resistance of a filament lamp as its temperature increases
resistance increases
what happens to the resistance of a thermistor as temperature increases
resistance decreases
what happens to the resistance of a lightt dependant resistor when light intensity decreases
resistance decreases
