Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > 4.2 Energy, power and resistance > Flashcards

4.2 Energy, power and resistance Flashcards

1
Q

What is the definition of electromotive force?

A

The energy gained per unit charge by passing through the supply, when a form of energy is transferred to electrical energy carried by the charges.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the definition of potential difference?

A

The energy transferred per unit charge by the charges passing through the component.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are e.m.f and p.d both measured in?

A

Volts (v) or joules per coulomb (JC^-1).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where is e.m.f measured?

A

At a supply.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where is p.d measured?

A

Across a component.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the equation for e.m.f?

A

e.m.f = energy transferred / charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the equation for p.d?

A

p.d = work done / charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are e.m.f and p.d measured by?

A

A voltmeter connected in parallel with a supply or component.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens when an electron is accelerated by a voltage?

A

The electron gains energy equal to eV, this energy is also equal to the kinetic energy of an electron, Ek = 1/2mv^2.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the resistance of an ammeter assumed to be?

A

Very small so that it doesn’t affect the circuit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the resistance of a voltmeter assumed to be?

A

Very high so that it doesn’t affect the circuit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is Kirchhoff’s second law?

A

Around any series circuit, the sum of the e.m.fs is equal to the sum of the p.ds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do current and voltage behave in a series circuit?

A

Current is the same at any point, voltage splits up over each component.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do current and voltage behave in a parallel circuit?

A

Current splits up down each branch, voltage is the same across each branch.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the equation for resistance?

A

Resistance = voltage / current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is resistance measured in?

A

Ohms (Ω).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the relationship between voltage and current across a fixed resistor?

A

Voltage is directly proportional to current.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does Ohm’s Law state?

A

The voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperature, remain constant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What factors affect electrical resistance?

A

The material the wire is made from, the length of the wire, the cross-sectional area of the wire, the temperature of the wire.

20
Q

What are features of LEDs?

A

Switch on instantly, very robust, very versatile, operate with low potentials, long working life, more efficient than incandescent light bulbs.

21
Q

What does a thermistor do?

A

Changes its resistance based on the surrounding temperature (higher temperature = lower resistance).

22
Q

What does an LDR do?

A

Changes its resistance based on the surrounding light intensity (higher light intensity = lower resistance).

23
Q

What is the explanation for the VI graph for a filament lamp?

A

As more pd is applied across the filament, it heats up more, increasing its resistance and reducing the rate of increase of current flow with increasing pd.

24
Q

What is the explanation for a graph of temperature against resistance?

A

As temperature increases, ions vibrate more so there are more delocalised electrons meaning more current can be carried so resistance decreases.

25
Q

What is the equation for the resistivity of a wire?

A

Resistivity = (resistance x cross-sectional area) / length of wire (ρ = (R x A) / L)

26
Q

Why are resistivity values given at a specific temperature?

A

Resistivity changes with temperature.

27
Q

What equation is used to find the actual resistivity of a material?

A

ρT = ρO [1 + α (T - TO)]

28
Q

What does ρT in the resistivity and temperature equation represent?

A

The resistivity at temperature T.

29
Q

What does ρO in the resistivity and temperature equation represent?

A

The resistivity at reference temperature (usually 20 degrees Celsius).

30
Q

What does α in the resistivity and temperature equation represent?

A

The temperature coefficient of the material.

31
Q

What does TO in the resistivity and temperature equation represent?

A

The temperature for which the resistivity value is quoted.

32
Q

What does T in the resistivity and temperature equation represent?

A

The temperature of the material.

33
Q

What is the temperature coefficient?

A

A constant that symbolises the resistance change factor per degree of temperature change.

34
Q

What is the value of α for pure metals?

A

Positive as when temperature increases, resistance increases.

35
Q

What is the value of α for semi conductors?

A

Negative as when temperature increases, resistance decreases.

36
Q

What happens as the value of α gets closer to 0?

A

The material’s conductivity is affected less by temperature.

37
Q

What is power measured in?

A

Watts (W).

38
Q

What is the equation for power using current and voltage?

A

Power = current x voltage (P = I x V)

39
Q

What is the equation for power using current and resistance?

A

Power = current^2 x resistance (P = I^2 x R)

40
Q

What is the equation for power using voltage and resistance?

A

Power = voltage^2 / resistance (P = V^2 / R)

41
Q

What is the equation for power using energy transferred and time?

A

Power = energy transferred / time (P = E / t)

42
Q

What two things does the cost of electricity depend on?

A

The power rating of the appliance (in kilowatts), how long the appliance is left on for (in hours).

43
Q

What is electricity measured in?

A

‘Units’ (kilowatt hours)

44
Q

What is the equation for the number of electrical units?

A

Number of units = power x time

45
Q

What is the equation for the cost of electricity?

A

Cost = number of units x cost of each unit

46
Q
A

Physics (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions