2. Electricity Flashcards
What is the size of the nucleus of an atom?
One thousandth of the atom.
What do insulators do?
Allow charge to build up.
What do conductors do?
Allow charge to flow through them.
How do you get a static shock?
When a balloon rubs against a jumper, the friction causes the electrons in the jumper to move to the balloon. The balloon now has a negative charge and the jumper a positive charge. The jumper is EARTHED. The balloon is then attracted to the jumper as positive attracts negative charge. They therefore stick to each other.
What are electric fields?
The two charged objects do not have to be touching to experience a force. Therefore, this is a non-contact force. It is the area around a charged object where if you put another charged object into that area it will experience a force.
How do you draw electric fields?
The arrows point in the direction that a positive charge would move if placed in the field.
What is current?
A measure of the rate of flow of electric charge in a circuit. It is measures in amperes using an ammeter.
Charge = current x time (what are the units?)
Charge= coulombs (C)
Current= amps (A)
Time = seconds (s)
Why do electrons flow?
Due to potential difference.
What is potential difference?
A measure of the difference in potential energy between two points in a circuit. Potential difference is also called voltage. It is measured in volts using a voltmeter.
Energy = charge x potential difference (what are the units?)
Energy= joules (J)
Charge = coulombs (C)
Potential difference= volts (V)
Potential difference= currrent x resistance (what are the units)
Potential difference = volts (V)
Current = amps (A)
Resistance = ohms
What happens if the resistance increases in a circuit?
The potential difference increases but the current decreases.
What happens if the resistance decreases in a circuit?
The current increases but the potential difference decreases.
What is a series circuit?
A circuit that has all its components wired in the same continuous loop so there is only one path for the electrons to flow through.
What are the rules of a series circuit?
- there is the same current through each component
- the total potential difference of the power supply is shared between the components
- the total resistance of 2 components is the sum of the resistance of each component
What is a parallel circuit?
A circuit that contains a point (junction) where the current can split or join.
What are the rules of a parallel circuit?
- the potential difference across each component is the same
- the total current through the whole circuit = sum of currents through separate components
- total resistance of 2 resistors = less than the resistance of the smallest individual resistor
What is a thermistor and what is it used for?
A circuit component that can be used for temperature control and sensing, controlling devices that change depending on temperature and in digital thermometers
What happens in a thermistor at a low temperature?
Resistance is high.
What happens in a thermistor at a high temperature?
Resistance is low.
What is a light dependent resistor and what is it used for?
They are used to detect light levels- e.g. in security lights that are automatic.
What happens to a light dependent resistor in the dark?
Resistance is high.
What happens to a light dependent resistor in the light?
Resistance is low.
What is direct current and what is it produced by?
An electrical current that always flows in one direction- produced by cells and batteries.
What is an alternating current and what is it produced by?
An electric current that is constantly changing direction- produced by most generators and used in mains electricity.
What frequency does the AC supply have in the UK?
50 Hz
What potential difference does the AC supply have in the UK?
230V
What is the period of an AC supply?
The time taken for one complete oscillation.
What is the frequency of an AC supply?
The number of oscillations per second.
What colour is the live wire?
Brown
What is the function of the live wire?
Carries the alternating potential difference from the power supply.
What is the PD of a live wire?
230V
What colour is the neutral wire?
Blue
What is the function of the neutral wire?
To complete the circuit from the appliance back to the supply.
What is the PD of a neutral wire?
0V
What is the colour of an earth wire?
Green and/or yellow
What is the function of the earth wire?
It does not form part of the normal circuit but it is there for safety.
What is the PD of the earth wire?
0V
What is power?
The rate of transfer of energy.
Energy transferred = power x time (what are the units?)
Energy transferred= joules (J)
Power= watts (W)
Time= seconds (s)
Power = current x voltage (what are the units?)
Power= watts (W)
Current= amps (A)
Voltage= volts (V)
Power = current2 x resistance (what are the units?)
Power= watts (W)
Current= amps (A)
Resistance= ohms
What are some rules about efficiency?
It is always LESS than one and has NO unit.
What is the national grid?
A network of cables and transformers designed to carry mains electricity around the country from the power stations where it is generated to the homes and factories where is it used.
Why is a low current used in terms of energy?
Less energy is transferred to the surroundings as heat from the cables. This increases the efficiency.
What does a step up transformer do?
Increases the PD, decreases the current
What does a step down transformer do?
Decreases the PD, increases the current
