Electricity - GCSE Flashcards
Name 3 hazards that come with electricity
Damaged insulation
Overheating of cables
Damp conditions
How does damaged insulation pose a hazard
Contact with wire due to the gaps in the insulation can causes an electric shock or pose a fire hazards by creating a short circuit
How does overheating of cables pose a hazard
High currents passing through thin wire conductors cause the wires to heat up to very high temperatures which could melt the insulation and cause a fire
How do damp conditions pose a hazard
Water can conduct a current so wet electrical equipment can cause an electric shock
What is a fuse?
A thin piece of wire which overheats and melts if the current is too high, protecting the circuit.
They have a current rating which should be slightly higher than the current used by the device in the circuit.
What are circuit breakers?
They consist of an automatic electromagnet switch which breaks the circuit if the current rises over a certain value.
Why are circuit breakers better than fuses?
Because they can be reset and used again, and they operate faster.
How do earth wires prevent electric shocks?
They create a safe route for current to flow through in the case of a short circuit, preventing electric shocks
Why do earth wires have a very low resistance
So a strong current surges through them which breaks the fuse and disconnects the appliance
How does double insulation work?
Appliances either have plastic casings or have been designed so that the earth wire annoy touch the metal casing, preventing them from giving an electric shock
What is energy measured in?
Joules (J)
Energy is transferred from 1)________ energy in the battery to 2)_________ energy used by circuit components and then to the surroundings
1) chemical
2) electrical
What is power measured in?
Watts (W)
Give the equation for power using current (I) and voltage (v)
P = I x V
Give the equation for energy using current (I), voltage (V) and time (t)
E = I x V x t
What is direct current
Current that only flows in one direction
What is alternating current
Current that continuously changes direction
What is an alternating current supplied by?
Mains electricity
What is a direct current supplied by?
A cell or battery
What is current measured in?
Amperes (A)
What is current?
The rate of flow of charge at a point in the circuit
Describe current in metals
In metals, current is due to a flow of electrons
Because electrons are negatively charged, conventional current (which is the rate of flow of positive charge) is in the opposite direction to the flow of electrons
Current is conserved at a…
JUNCTION in a circuit because current is always conserved
What is potential difference measured in?
Volts (V) where 1V = 1JC
What is the definition for potential difference?
It is the work done per unit charge in moving between two points in the circuit
What is the equation for potential difference using energy (E) and charge (Q)?
V = E/Q
How is potential difference measured in a circuit?
It is measured with a voltmeter placed in a parallel across the component
What happens to the current when there is a high potential difference?
There is a greater current
What is resistance measured in?
Ohms
How is resistance measured?
Potential difference divided by the current
R = V/I
What happens to the current when there is a greater resistance?
It is harder for the current to flow through the component
What is an ohmic conductor?
When the current is directly portional to the voltage (such as resistor at a constant temperature)
I.e. it has a constant resistance
What is an non-ohmic conductor?
When the resistance changes as the voltage and current changes (such as a filament lamp)
When a circuit is connected in series…
Components are connected end to end in one loop
The same current flows through every component
The same potential difference is shared across each component
The total resistance is the sum of resistances of each component
When a circuit is connected in parallel…
Components are connected to the power supply in separate branches
The current is shared between each branch
The potential difference is the same across every branch
Why is connecting lamps in parallel advantageous?
Because if one breaks current can still pass through the rest
