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AQA: Combined Science Physics Higher > 2: Electricity > Flashcards

2: Electricity Flashcards

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1
Q

Define current

A

Electric current is the flow of electrical charge. The size of the electric current is the rate of flow of electrical charge.

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2
Q

State the equation that links charge flow and current.

A

Q = It

Q: Charge (coulombs, C)

I: Current (Amperes, A)

t: time (seconds, s)

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3
Q

Define potential difference.

A

Potential difference is a measure of energy, per unit charge, transferred between two points in a circuit. It is measured in volts, V.

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4
Q

State the equation that links potential difference, current and resistance.

A

V = IR

V: potential difference (volts, V)

I: current (amperes, A)

R: resistance (ohms, Ω)

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5
Q

Define resistance.

A

Resistance is the opposition to the flow of current. It is measured in ohms, Ω.

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5
Q

How is current and potential difference related in an ohmic conductor?

A

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means the resistance remains constant as the current changes.

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6
Q

How does resistance change with temperature in a filament lamp?

A

Resistance of a filament lamp increases as the temperature of the filament increases.

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7
Q

How does resistance change with potential difference in a diode?

A

The current in a diode flows in the positive direction only. Resistance is very high in the opposite direction.

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8
Q

How does resistance change with temperature in a thermistor?

A

The resistance of a thermistor decreases as temperature increases.

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9
Q

Describe how resistance changes with temperature in an ohmic conductor?

A

If the temperature of a metal conductor increases, the ions of the metal vibrate more vigorously. This increases the number of collisions between the free electrons. and the ions. Hence, for a metal, resistance increases with increasing temperature.

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10
Q

How does resistance change with light intensity in an LDR?

A

The resistance of an LDR decreases as light intensity increases.

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11
Q

What are the circuit rules of current, potential difference and resistance in a series circuit?

A
  • There is the same current through each component.
  • The total potential difference of the power supply is shared between the components.
  • The total resistance of the two components is the sum of the resistance of each component.
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12
Q

What are the circuit rules of current, potential difference and resistance in a parallel circuit?

A
  • The individual currents between the separate branches sums to the total current within the circuit.
  • The potential difference of the individual branches is the same and equal to that of the power source.
  • The total resistance of the separate branches is less than the resistance of the smallest resistor.
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13
Q

Describe the properties of the UK mains power supply.

A

The mains supply is AC (alternating current). It has a frequency of 50Hz and a potential difference of about 230V.

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14
Q

How are the different wires completing the mains supply easily identified?

A

They are colour coded:

Brown - Live wire

Blue - Neutral wire

Green and yellow stripes - Earth wire

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15
Q

What is the equation linking power, potential difference and current?

A

P = IV

P: power (watts, W)

I: Current (amperes, A)

V: Potential difference (volts, V)

16
Q

What is the equation linking power, current and resistance.

A

P = I²R

P: power (watts, W)

I: current (amperes, a)

R: resistance (ohms, Ω)

17
Q

What is the equation linking potential difference, energy transferred and time?

A

E = Pt

E: energy transferred, work done (joules, J)

P: power (watts, W)

t: time (seconds, s)

18
Q

What is the equation linking charge, potential difference and energy transferred?

A

E = QV

E: energy transferred, work done (joules, J)

Q: charge (coulombs, C)

V: potential difference (volts, v)

19
Q

What is the difference between a step-up transformer and a step-down transformer?

A

A step-up transformer increases the potential difference but loses some current as a result.

A step-down transformer decreases potential difference and gains some current as a result.

20
Q

What is the equation linking potential difference across primary coil and potential difference across secondary coil?

A

Potential difference across primary coil x current in primary coil = potential difference across secondary coil x current in secondary coil

21
Q

Required Practical Activity 15.1 (Pt1): What apparatus is required to investigate how the length of wire affects the resistance at a constant temperature.

A
  • A battery or suitable power supply
  • Ammeter
  • Voltmeter
  • Crocodile clips
  • Resistance wire attached to metre ruler
  • Connecting leads
22
Q

Required practical activity 15.1 (Pt2): State a method you could use to investigate how the length of wire affects the resistance at a constant temperature.

A

1: Set up the power supply, ammeter and metre ruler with resistance wire connected with crocodile clips in series with one being at the zero end of the ruler.

2: Set up a voltmeter in parallel with the metre ruler.

3: Decide the interval distance (e.g. 10cm) you will investigate and connect the first distance to be tested between crocodile clips A and B.

4: Measure the readings on the voltmeter and ammeter at this distance.

5: Record your results on a table with four columns: length of wire, potential difference in volts, current in amps and resistance in ohms.

6: Move crocodile clip B and record the readings for different lengths of wire e.g. 20cm, 30cm etc.

7: Calculate the resistance of each length of wire using the equation V = IR

8: Plot a graph of resistance against length of wire

9: Draw a line of best fit but it may not go through the origin.

23
Q

Required practical activity 15.2 (Pt1): What apparatus is required to investigate how the arrangement of resistors in series and parallel affects resistance.

A
  • A battery or suitable power supply
  • a switch
  • ammeter
  • voltmeter
  • crocodile clips
  • two 10 Ω resistors
  • connecting leads
24
Q

Required practical activity 15.2 (Pt2): State a method you could use to investigate how the arrangement of resistors in series and parallel affects resistance.

A

1: Set up the power supply, switch, the two resistors and ammeter in series. Set up the voltmeter in parallel with the two resistors.

2: Switch on and record the readings of the ammeter and voltmeter.

3: Calculate the total resistance of the series circuit.

4: Reset up the whole circuit with the power supply switch, the first resistor and the ammeter in series. Set up the second resistor in parallel with the first resistor and set up the voltmeter in parallel with the second resistor.

5: Switch on and record the readings of the ammeter and voltmeter.

6: Calculate the total resistance of the parallel circuit.

7: What conclusions can you make about the effect of adding resistors:
- in series
- in parallel

25
Q

Required practical activity 16.1 (Pt1): What apparatus is required to investigate current through a component when potential difference changes.

A
  • digital ammeter
  • digital voltmeter
  • element holders
  • a variable resistor
  • connecting leads
  • a filament lamp
  • a battery or suitable power supply
26
Q

Required practical activity 16.1 (Pt2): State a method you could use to investigate current through a component when potential difference changes.

A

1: Set up the power supply, ammeter, filament lamp and variable resistor in series. Connect the voltmeter in parallel with the filament lamp.

2: Record the readings on the ammeter and voltmeter.

3: Adjust the variable resistor and record the new readings on the ammeter and voltmeter.

4: Repeat this to obtain several pairs of readings.

5: Swap the connections on the battery/power supply. The ammeter is now connected to the negative terminal and the variable resistor to the positive terminal. The readings on the ammeter and voltmeter should now be negative.

6: Continue to record pairs of readings of current and potential difference with the battery reversed.

7: Plot a graph of current against potential difference. As the readings include negative values, the origin of the graph will be in the middle of the graph paper.

8: Draw a line of best fit through the origin. This is the characteristic of a filament lamp.

9: Repeat the experiment with a resistor and draw a line of best fit through the graph. This is the characteristic of a resistor.

27
Q

Required practical 16.2 (Pt1): What apparatus is required to investigate current through a diode when potential difference changes.

A
  • the circuit set up in activity 1
  • a millammeter
  • a diode
  • an extra resistor labeled P
28
Q

Required practical activity 16.2 (Pt2): State a method you could use to investigate current through a diode when potential difference changes.

A

1: Swap the leads on the battery/power supply back to their original positions

2: Reduce the battery/power supply potential difference to less than 5V.

3: Connect the extra resistor labelled P into the series circuit.

4: Replace the ammeter with the millammeter.

5: Replace the resistor used in activity 1 with a diode.

6: Record the readings on the millammeter and voltmeter in a suitable table.

7: Adjust the variable resistor and record the new millammeter and voltmeter readings.

8: Repeat this to obtain several pairs of readings.

9: Swap the connections on the battery/power supply. The millammeter is now connected to the negative terminal and the variable resistor to the positive terminal. The readings on the millammeter and voltmeter should now be negative.

10: Continue to record pairs of readings of current and potential difference with the battery reversed.

11: Plot a graph of current against potential difference. As the readings include negative values the origin of the graph paper will be in the middle of the graph paper.

12: You should now be able to draw a line of best fit through the graph paper. This is the characteristic of a diode.

AQA: Combined Science Physics Higher (7 decks)

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