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Physics GCSE > P5. Electricity in the home > Flashcards

P5. Electricity in the home Flashcards

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1
Q

Is mains electricty an a.c supply or d.c supply? What do each of these stand for

A

Mains electricity is an a.c supply

a.c. : Alternating current

d.c. : Direct current

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2
Q

Define alternating current and direct current

A

Alternating current: Current that continuously changes direction at a specific frequency
Direct current: One directional current flow

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3
Q

What is the frequency and voltage of the UK mains electricity supply?

A

Frequency: 50 Hz
Voltage: 230V

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4
Q

How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires

A
  1. Live wire
  2. Neutral wire
  3. Earth wire
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5
Q

State the insulation colour used on the Earth wire.

A

Green and yellow stripes

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6
Q

State the insulation colour used on the live wire.

A

Brown

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7
Q

State the insulation colour used on the neutral wire

A

Blue

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8
Q

Explain when the Earth wire does and doesn’t carry a current.

A

Under normal circumstances, no current flow through the Earth wire
If a fault occurs in the appliance (such as the surge or the casing becoming live), current will flow to the ground

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9
Q

What potential is the neutral wire at?

A

0 volts

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10
Q

State the potential difference between the live and earth wires.

A

230 volts

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11
Q

What is the purpose of the neutral wire?

A

To complete the circuit by connecting the appliance back to the mains supply

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12
Q

For metal appliances, where is the Earth wire connected to? Why?

A

Earth wire is connected to the metal casing of the appliance
If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution

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13
Q

State two equations for the power of a circuit. Give appropriate units

A

P = I V P = I² R

Power (Watts) = Current (Amperes) x Potential difference (volts)
Power (Watts) = Current² (Amperes) x Resistance (Ohms)

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14
Q

State an equation linking energy transferred, power and time. Give appropriate units

A

E = P t

Energy (Joules) = Power (Watts) × Time (Seconds)

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15
Q

State an equation linking energy transferred, power and time. Give appropriate units

A

E = Q V

Energy (Joules) = Charge (Coulombs) × Potential Difference (Volts)

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16
Q

What two main factors does the amount of energy transferred by an appliance depend on?

A
  1. How long the appliance is being used for
  2. The power of the appliance
17
Q

Describe the energy transfers in a battery powered torch.

A

Battery converts chemical energy into electrical energy
Bulb converts electrical energy into light as well as waste energy in the form of heating

18
Q

Describe the energy transfers in a battery powered motor

A

Battery converts chemical energy into electrical energy
Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction

19
Q

What three things determine the power of a circuit device?

A
  1. The potential difference across the circuit
  2. The current through the circuit
  3. The amount of energy transferred in a given time
20
Q

What is the purpose of the National Grid?

A

To link power stations to consumers so that they have access to a source of electricity

21
Q

What are two types of transformers used in the National Grid?

A
  1. Step-Up Transformers
  2. Step-Down Transformers
22
Q

Where are step-up transformers found in the National Grid? What do they do?

A

Step-Up Transformers are used when connecting power stations to transmission cables
They increase the potential difference

23
Q

What are step-down transformers found in the National Grid? What do they do?

A

Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)
They decrease the potential difference

24
Q

Why do transmission limes transfer electricity at high potentials?

A

A high potential, results in a low current
The lower the current, the less energy that is wasted as heat
Therefore it is more efficient

25
Q

Why does the potential need to be decreased between transmission lines and houses?

A

Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
Appliances are designed for 230V

26
Q

What can happen when insulating materials are rubbed together?

A

They can become (statically) electrically charged

27
Q

Why can insulators become electrically charged when rubbed together?

A

Electrons are rubbed from one material onto the other
The material gaining electrons becomes negatively charged
The material losing electrons becomes equally positively charged

28
Q

What happens when two electrically charged objects are brought close together?

A

They exert a force on each other

29
Q

What happens when two identically charged objects are brought close together?

A

They exert a repulsive force on each other and repel

30
Q

What happens when two oppositely charged objects are brought close together?

A

They exert an attractive force on each other and attract

31
Q

Give an example of a non-contact force

A

The repulsive or attractive force acting between two electrically charged objects

32
Q

What is an electric field?

A

A region in which a charged object will experience a non-contact electrical force

33
Q

Where can electric fields be found?

A

Surrounding any charged object

34
Q

Describe the electric field around a charged particle.

A

Strongest closest to the object
Decreases in strength as you move away from the object

35
Q

What happens to the force between two charged objects when they are moved closer together?

A

The forces between them becomes stronger as the separation reduces

36
Q

In situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?

A

Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials.

Physics GCSE (11 decks)

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