P5 - Electricity in the home Flashcards
What is an alternating current?
Electric current in a circuit that repeatedly reverses its direction
What is a direct current?
Electric current in a circuit that is in one direction only
What is a fuse?
A fuse contains a thin wire that melts and cuts the current off if too much current passes through it
What is an oscilloscope?
A device used to display the shape of an electrical wave
What are step down transformers?
Electrical device used to step down the size of an alternating potential difference
What are step-up transformers?
Electrical device used to step-up the size of an alternating potential difference
What is electrical power?
The rate of energy transfer by each electrical component
What are the 3 equation for power
- Power = Energy / time
- Power = Current x Potential Difference
- Power = Current² x Resistance
What is the unit for power?
Watt
What are the 4 types of domestic fuses?
- 1A
- 3A
- 5A
- 13A
How do you determine what fuse to use?
Electrical power / potential difference = fuse rating (current) [You always round up to the fuse rating]
Why is it a bad idea to use an incorrect fuse?
- A fuse that is too low will fail almost immediately, breaking the circuit
- A fuse that is too big will fail to break the circuit if the current is too large, this can cause damage to the circuit such as burning the insulation or melting the wire. It could even start a fire.
What fuse would you use if the current through a circuit is 2.2A and why?
You would use a 3A fuse because it would not melt when the correct current is flowing through the circuit, however if the current becomes too high it would fail, protecting the house
What is the potential difference of the mains supply?
230 Volts
What fuse would you use if the current in a circuit was 9.1A?
You would use a 13A fuse as the fuse would not melt if the correct current if flowing through the circuit, however it would fail and protect the house if the current is too high
What are the 2 equations for voltage?
- V = IR
* V = E / Q
What forces charge around a circuit?
Potential difference
What is charge carried around the circuit by?
electrons
What is the equation for charge flow?
Charge flow = current x time
What is 1 coulomb?
6.242 x 10^18 protons or electrons
What is the current is 31.21 x 10^18 electrons flow each second?
5A
Describe how resistors are heated
Electrons flowing through the resistor constantly collide with the vibrating metal ions in the resistor, transferring energy to the metal ions. The metal ions gain energy to their kinetic energy stores and vibrate more, this causes the resistor to get hotter. The resistor heats the surroundings, dissipating the energy supplied to the surroundings
What is the rule for potential difference in series circuits?
Potential difference is shared across components in series
Describe the energy store changes in a circuit containing a bulb
The chemical energy store of the battery decreases as it transfers energy by an electric current, increasing the thermal energy store of the bulb and variable resistor. Energy is then transferred to the surroundings as heat and light
What is energy efficiency?
The ratio of useful energy output from a device to total energy input of a device
What is the equation for energy efficiency?
Energy efficiency = useful output energy / total input energy
Energy efficiency = useful output power/ total input power
What are the units of efficiency?
There are no units as it is a ratio
Why can no device be more than 100% efficient?
Because the law of conservation of energy states that energy cannot be created or destroyed
Why is it useful to know what type of energy is being transferred and in what amounts by a device?
To discover how efficient the device is
What is the equation for useful power?
useful power = efficiency x input power
What is the equation for kilowatt hours?
(Power [Watts] x time [hours]) / 1000
What is 1kWh in Joules?
3600000 J
What is 1 kWh?
1 kWh is the electrical energy converted by a 1 kW appliance used for 1 hour.
What useful energy does a lightbulb produce?
Light radiation
What is the role of step-up transformers?
Step-up transformers are used at power stations to transfer electricity to the national grid. These transformers are used to make the size of the alternating potential difference much larger, typically from 25 000 V to 132 000 V
What is the role of step-down transformers?
Step-down transformers are sued to supply electricity from the national grid to consumers. Homes and offices in the UK are supplied with mains electricity that provides the same power as a 230V DC supply. Factories use much more power than homes so are supplied with a high p.d
What is the purpose of transformers in the national grid?
By making the grid potential difference very large, much less current is needed to transfer the same amount of power (high p.d, low current). So the power loss due to resistance heating in the cables is much reduced as lots of energy is lost when there is a high current. This means that the national grid is an efficient way to transfer power
What equation can be used to calculate the energy transferred to a component by a flow of charge?
E = V x Q
What is the total energy transferred by the supply equal to?
The sum of the energies transferred to each component of the circuit
Describe how electrical appliances waste energy?
Electrical appliances waste energy because the current in the wires and component of the appliance has a heating effect due to the resistance of the wires and the components. So they transfer energy by heating to the surroundings.
How much energy dose each coulomb of charge carry in a 12V battery/
12J
If the voltmeter reads 10V, what is the energy transfer to the variable resistor per second if the current is 1A
2J
How is a charge supplied with energy?
Energy is supplied to the charge at the power source, increasing the potential difference
What does it mean if a battery has a larger potential difference?
It supplies more energy to the circuit for every coulomb of charge that which flows round it
What is a live wire?
a wire carrying an electric current
