P5- Domestic electricity 🔌

Question 1

How does a blender transfer energy?

Hint: why?

Answer 1

• 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]

Question 2

How does a fan transfer energy ?

Hint: thermal energy

Answer 2

• 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]

Question 3

How does an iron transfer energy ?

Hint: don’t generate

Answer 3

• 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]

Question 4

How does a kettle transfer energy ?

Hint: mains ac

Answer 4

• 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]

Question 5

How does a hair dryer transfer energy ?

Hint: motor

Answer 5

• 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.

Question 6

How does a washing machine transfer energy ?

Answer 6

• 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.

Question 7

RECAP: What is power ?

Answer 7

• 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]

Question 8

• Fill in the gaps: appliances which are designed to generate ________ energy, usually have a much ______ power rating than appliances designed to generate kinetic energy.

Answer 8

• appliances which are designed to generate thermal energy, usually have a much higher power rating than appliances designed to generate kinetic energy.

Question 9

No appliance completely transfer all energy usefully.

The higher the current, what will happen to the energy transferred ?

Answer 9

• the higher the current, the more energy is transferred to the thermal energy stores of the components. [and the surroundings]

Question 10

What is direct current [dc] ?

Answer 10

• direct current is [current from a cell or battery,] that always flows in the same direction.

Question 11

What is alternating current [ac] ?

Answer 11

• alternating current, is current that is constantly changing direction.

Question 12

In the UK, what type of current is the mains electricity?

Answer 12

• the mains electricity in the UK is alternating current.

Question 13

What is the main benefit of using alternating current ?

Answer 13

• 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.

Question 14

What is the frequency of the UK’s domestic electricity supply ?

Answer 14

• the frequency of the UK’s domestic electricity supply, is 50 Hz [hertz]

Question 15

What is the potential difference of the UK’s domestic electricity supply ?

Answer 15

• the potential difference of the UK’s domestic electricity supply is 230V.

Question 16

What’s an oscilloscope ?

Answer 16

• an oscilloscope is used to see the pattern of current.

Question 17

In a oscilloscope, how can we calculate the frequency

Answer 17

• [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.

Question 18

How are electrical appliances in the UK, normally connected to the mains supply ?

Hint: cables

Answer 18

• 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.

Question 19

What is the defenition of ‘the live wire ?’

Hint: carries

Answer 19

• the live wire, is the browned colour wire that carries alternating current from the supply, in a mains power supply.

Question 20

What is the neutral wire ? [3]

Hint: mains power supply

Answer 20

• the neutral wire, is a [/the]blue coloured wire that completes the circuit in a mains power supply

Question 21

What is the definition of ‘the earth wire ?’

Answer 21

• the earth wire, connect the metal case of an appliance to the earth in a mains cable

Question 22

Explain how the earth wire works ? [3]

Hint: metal case

Answer 22

• 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].

Question 23

If the switch is open, there can still be a risk of electric shock. Why ?

Hint: part

Answer 23

• 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.

Question 24

Why is any connection between live and earth dangerous ?

Hint: 🔥

Hint #2: huge current

Answer 24

• 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]

Question 25

What can you tell me about direct and alternating current, in an oscilloscope

Answer 25

• 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.

Question 26

• 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.

Answer 26

• 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.

Question 27

How can the live wire be dangerous ?

Hint: 0V

Answer 27

• 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.

Question 28

What colour is the neutral wire ?

Answer 28

• 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.]

Question 29

What colour is the earth wire ?

Answer 29

the earth wire is green-and-yellow striped. It’s a safety wire, to stop the from becoming live.