P5- Domestic electricity 🔌 Flashcards
How does a blender transfer energy?
Hint: why?
- electrical energy—> kinetic energy of motors because the main purpose of these appliances is to movement.
- The blender moves to mix the food; due to friction in the motors, a small amount of thermal energy will also be generated. [not intended]
How does a fan transfer energy ?
Hint: thermal energy
- electrical energy—> kinetic energy of motors because the main purpose of these appliances is to movement.
- the fan moves to create air currents; due to friction in the motors, a small amount of thermal energy will also be generated. [not intended]
How does an iron transfer energy ?
Hint: don’t generate
- electrical energy—-> thermal energy
- electrical energy from the mains, is transferred to thermal energy- since the appliances are designed to get hot. [they don’t generate kinetic energy]
How does a kettle transfer energy ?
Hint: mains ac
- electrical energy—-> thermal energy
- electrical energy from the mains ac supply, is transferred to the thermal energy store, of the heating element inside the kettle.
- since the appliances are designed to get hot. [they don’t generate kinetic energy]
How does a hair dryer transfer energy ?
Hint: motor
- electrical energy—> kinetic energy of electric motors + thermal energy
- This appliance uses electrical energy and it transfers electrical energy, to kinetic energy of the electric motors + thermal energy.
- A motor moves air through the hair dryer, and the heating element heats the air.
How does a washing machine transfer energy ?
- electrical energy—> kinetic energy of electric motors + thermal energy
- This appliance uses electrical energy and it transfers electrical energy, to kinetic energy of the electric motors + thermal energy.
- a heating element heats the water, and a motor turns the drum to wash the clothes.
RECAP: What is power ?
- power is, the rate at which energy is transferred.
- OR the rate at which work is done
- [1W, is an energy transfer of 1J per second]
- Fill in the gaps: appliances which are designed to generate ________ energy, usually have a much ______ power rating than appliances designed to generate kinetic energy.
- appliances which are designed to generate thermal energy, usually have a much higher power rating than appliances designed to generate kinetic energy.
No appliance completely transfer all energy usefully.
The higher the current, what will happen to the energy transferred ?
- the higher the current, the more energy is transferred to the thermal energy stores of the components. [and the surroundings]
What is direct current [dc] ?
- direct current is [current from a cell or battery,] that always flows in the same direction.
What is alternating current [ac] ?
- alternating current, is current that is constantly changing direction.
In the UK, what type of current is the mains electricity?
- the mains electricity in the UK is alternating current.
What is the main benefit of using alternating current ?
- the main benefit of using alternating current is:
- it’s easier to use a transformer, to increase or decrease the potential difference, than it is with direct current.
What is the frequency of the UK’s domestic electricity supply ?
- the frequency of the UK’s domestic electricity supply, is 50 Hz [hertz]
What is the potential difference of the UK’s domestic electricity supply ?
- the potential difference of the UK’s domestic electricity supply is 230V.
What’s an oscilloscope ?
- an oscilloscope is used to see the pattern of current.
In a oscilloscope, how can we calculate the frequency
- [Periodic time for one cycle [T] = divisions x timebase]
- Frequency [F], F= 1/T
- first work out the time from one peak, to the next peak- this shows one complete cycle.
- look at the time interval: the time between the peak.
How are electrical appliances in the UK, normally connected to the mains supply ?
Hint: cables
- electrical appliances in the UK, normally connected to the mains supply by three core cables.
- there are three wires that are made of copper- and copper is a good conductor of electricity; the coatings of the wires are made of plastic and they don’t conduct electricity.
What is the defenition of ‘the live wire ?’
Hint: carries
- the live wire, is the browned colour wire that carries alternating current from the supply, in a mains power supply.
What is the neutral wire ? [3]
Hint: mains power supply
- the neutral wire, is a [/the]blue coloured wire that completes the circuit in a mains power supply
What is the definition of ‘the earth wire ?’
- the earth wire, connect the metal case of an appliance to the earth in a mains cable
Explain how the earth wire works ? [3]
Hint: metal case
- the metal case of an appliance is connected into the Earth wire and the Earth wire is connected into the ground, with a metal rod.
- This means that if the case becomes live, a huge current flows to the Earth. The fuse then melts, shutting off the current. [as it breaks the circuit]
- This is what prevents anyone from getting an electric shock from touching the case, of an appliance [if the live wire touches it].
If the switch is open, there can still be a risk of electric shock. Why ?
Hint: part
- even if the switch is opened [e.g- plug socket or light switch turned off] the first part of the live wire running to the switch, still has a potential difference of 230V.
- so if you made contact with the live wire, your body provides a connection between the supply and the earth- current would still flow through you.
Why is any connection between live and earth dangerous ?
Hint: 🔥
Hint #2: huge current
- any connection between live and earth dangerous, because if the connection creates a low-resistance path to the earth, a huge current flows. [this could result in a fire hazard]
What can you tell me about direct and alternating current, in an oscilloscope
- in an alternating current: the potential difference is rising and falling-this shows the current is moving backwards and forwards.
- the height of the peak, tells us the maximum potential difference.
- in a direct current: the potential difference doesn’t change and is therefore a flat line.
- Fill in the gaps: the live wire is _____ and this can be remembered by- Br [bottom right] ____ because it’s always the bottom right wire.
- ; the live wire also carries the ___________ potential difference [of 230V], from the mains supply and is also connected to a ____ in the plug.
- the live wire is brown and this can be remembered by- Br [bottom right] brown, because it’s always the bottom right wire.
- the live wire also carries the alternating potential difference [of 230V], from the mains supply and is also connected to a fuse in the plug.
How can the live wire be dangerous ?
Hint: 0V
- the live wire can be extremely dangerous, and could easily be fatal if touched- since your body, [just like the earth] is at 0V.
- meaning that if you touch the wire, a large potential difference [of 230V] is produced across your body, allowing a current to flow through you into the earth- which electrocutes you.
What colour is the neutral wire ?
- the neutral wire is blue and this can be remembered by- Bl [bottom left] blue, because it’s always the bottom left wire.
- the neutral wire completes the circut, having a potential difference of 0V.
- [when the appliance is operating normally, current flows through the live and neutral wires.]
What colour is the earth wire ?
the earth wire is green-and-yellow striped. It’s a safety wire, to stop the from becoming live.
