Electricity 2 Flashcards
The home, national grid, energy transfer, electrical fields, electricity.
What are the stages of the national grid? (steps 1 -3)
- Electric power is generated at a power station.
- Step up transformers (between power stations and transmission lines) increase voltage and decrease current.
- The electrical power is transmitted via the national grid at low current which minimises power and energy loss (efficient).
What are the stages of the national grid? (steps 4 and 5)
- Step down transformers (between transmission lines and domestic buildings) decrease voltage and increase current near our homes.
- Electric power is wired into our homes at a voltage that is relatively safe to use (230V).
Why is a high current bad when transmitting electricity?
A high current generates a lot of wasted heat because the wire heats up, and energy is lost as thermal energy to the surroundings.
What are the three wires in UK plugs?
Live wire
Neutral wire
Earth wire
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
What colour is the earth wire?
Green and yellow stripes.
How does the earth wire work to prevent an appliance becoming live?
-The earth wire is connected to the casing of the appliance.
-If the live wire touches the appliance casing, the earth wire provides an alternative pathway for electricity to flow.
-This way, we don’t get an electric shock from touching the live appliance casing.
What are the risks of surges in current?
Electric shocks, fires, damage to appliance.
Safety features of UK plugs.
-Fuse
-Circuit breakers
-Double insulation
-Earth wire
What does a fuse do?
Melts if the current through it is too high, which breaks the circuit.
What is a fuse’s rating?
The current at which a fuse breaks a circuit.
What are circuit breakers?
Fuses that can be reset and reused.
What is double insulation in terms of UK plugs?
Plastic casing, but no earth wire, so that electricity is not conducted to things the wire touches.
Where are electric fields found?
Around all charged objects.
Electrical field lines run…
…from positive to negative.
The closer to a charged object…
…the stronger the electric field (and the closer the field lines).
Ionisation (physics)
The physical process of atoms loosing or gaining electrons.
A strongly charged object can ionise the air, which means the air looses some of its electrons and conducts electricity.
What is an electrical field?
A region in which a charged object will experience a non-contact electrical force.
What is static electricity?
The build up of electrical charge on insulating materials.
Explain how rubbing an acetate rod with a cloth causes the rod and cloth to become charged (static electricity).
- Friction between the cloth and rod causes electrons to move to the cloth.
-The cloth is now negatively charged and the rod is positively charged.
Describe what happens when two electrically charged object are brought close to each other.
The charged objects exert a force on one another.
If two objects have the same type of electrical charge, they repel each other.
If they have different types of electrical charge, they attract one another.
How can we prevent static charge?
Earth two rubbing materials so that charge flows off of them to the ground.
What is an electrical conductor?
A material capable of transferring electrical energy (carrying charge) because its electrons are delocalised and can flow
A device has higher power if..?
It transfers more energy in a shorter time.
Explain why electrical power is transmitted at high voltage and low current on the National Grid.
Because the amount of electrical energy wasted as thermal energy is proportional to the square of the current, from the equation
P = I²R.
For example, if the current got 10x bigger, then 100x more energy would be lost as heat each second.