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GCSE AQA physics > Topic 2- Electricity: > Flashcards

Topic 2- Electricity: Flashcards

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1
Q

What is energy efficiency?

A

A higher percentage of energy input is usefully transferred.

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2
Q

What is electric current?

A

The flow of electrical charge.

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3
Q

What can be said aout the value of current at any point in a single closed loop?

A

Current is the same at all points in a closed loop.

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4
Q

What two factors does the current in a circut depend on?

A
  • Potential difference (V)
  • Resistance (R)
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5
Q

What is an ‘ohmic conductor’? State the condition required.

A
  • A conductor for which current and potential difference are directly proportional.
  • Resistance remains constant as current changes
  • Temperature must be constant
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6
Q

List four components for which resistance is not constant as current changes.

A

1) Lamps
2) Diodes
3) Thermistors
4) Light dependant resistors (LDR’s)

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7
Q

What happens to the resistance of a filament lamp as temperature increases? Why?

A
  • Resistance increases
  • Ions in the metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow.
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8
Q

What is different about current flow through a diode?

A
  • The current only flows in one direction
  • Resistance is very high on the other end, preventing current flow
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9
Q

What happens to the resistance of a thermistor as temperature increases?

A

The thermistor’s resistance decreases.

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10
Q

Give two examples of when a thermistor may be used.

A
  • In a thermostat- to turn a heater on to a certain temperature.
  • In a freezer to turn on a cooler when the temperature becomes too high.
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11
Q

What happens to the resistance of the LDR as light intensity DECREASES?

A

The LDR’s resistance increases.

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12
Q

Give an appliaction for an LDR.

A
  • Street lights
  • When ilght levels become too low, the light gains sufficient current to turn on
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13
Q

What are two ways that a component can be connected in a circut?

A
  • Series
  • Parallel
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14
Q

How does p.d. accross two components vary when connected in series and parallel?

A
  • Series: total p.d. is shared between each component
  • Parallel: p.d. is the same accross each component
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15
Q

If 2 resistors are connected in parallel, what can be said about their combined total resistance?

A
  • Their total resistance is less than the smallest of the 2 individual resistors.
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16
Q

If two resistors are connected in series, what can be said about their total resistance?

A

Their total combined resistance is equal to the sum of the two individual resistances.

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17
Q

Describe the current in a series cicut.

A
  • The current is the same at all positions
  • Because the charge has only one path to flow through
18
Q

Describe the current in a parallel circut.

A
  • The current is shared between different branches
  • When the charge reaches a junction, it splits.
19
Q

How is an ammeter connected to measure current?

A

In series with the component that tthey are measuring current through.

20
Q

How is a volmeter connected to measure p.d.?

A

Voltmeters should be connected parallel to the commponent they are measuring the p.d. of.

21
Q

Why is it advantageous to connect lamps in parallel?

A
  • If one lamp blows
  • The rest are unaffected and can still recieve the current (the circut is still complete)
22
Q

Is mains an a.c supply or a d.c supply?

A

Mains is an a.c. supply.

23
Q

Define alternating current and direct current.

A
  • Alternating current: Current that continuosly changes direction at a specific frequency
  • Direct current: One directional current flow
24
Q

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

A
  • Frequency: 50 Hz
  • Voltage: 230 V
25
Q

What three wires found in cables connect electricity appliances to the mains?

A
  • Live wire 🟤
  • Neutral wire 🔵
  • Earth wire 🟡🟢
26
Q

Explain why the earth wire may/ may not carry a current.

A
  • Under normal circumstances, the earth wire does not carry a current.
  • If a fault occurs in the appliance, a large current will flow to the ground, as the wire has virtually no resistance. This causes the fuse to blow, preventing any further current flow.
27
Q

What potential is the neutral wire at?

A

0 V

28
Q

State the potential difference between the live wire and earth wire.

A

230 Volts

29
Q

What is the purpose of the neutral wire?

A

To complete the circut by connecting the appliance back to the mains supply.

30
Q

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

A
  • The earth wire is connected to the metal casing of the appliance.
  • If the live wire becomes loose and touches the casing, the current will flow through the earth wire, preventing electrocution.
31
Q

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

A

1) How long the applance is being used for
2) The power of the appliance

32
Q

Describe the energy transfer in a battery powered torch.

A
  • The battery converts chemical energy into electrical energy
  • The bulb converts electrical energy into light as well as waste energy in the form of heating.
33
Q

Describe the energy transfers in a battery powered motor.

A
  • Battery converts chemical energy into electrical enrgy.
  • Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to** friction.**
34
Q

What 3 things determine the power of a circut device?

A

1) The p.d. accross the circut
2) The current through the circut
3) The amount of energy transferred in a given time

35
Q

Whatis the purpose of the national grid?

A

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

36
Q

What are the 2 types of transformers used in the national grid?

A
  • Step-up transformers
  • Step-down ransformers
37
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 p.d.
38
Q

Where 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)
  • The decrease the p.d.
39
Q

Why do transmission lines transfer energy at a high potential difference?

A
  • A high potential difference results in a low current
  • The lower the current, the less energy is wasted as heat
  • Therefore it is more efficient
40
Q

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

A
  • A lower p.d. is safer for domestic use
  • So it reduces the likelyhood of a severe electrocution
  • Appliances are designed for 230 V
41
Q

What happens when 2 insulating materials are rubbed together?

A

GCSE AQA physics (3 decks)

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