# 4.2 Energy, Power and Resistance Flashcards Preview

## Physics A Level > 4.2 Energy, Power and Resistance > Flashcards

Flashcards in 4.2 Energy, Power and Resistance Deck (24)
1
Q

What is potential difference? (2)

A

A measure of the energy provided to the charge carriers in order for them to convert it into other forms of energy
The amount of work done per unit charge

2
Q

What is electromotive force?

A

The energy transferred from one type of energy to electrical energy per unit charge

3
Q

What is the difference between potential difference and electromotive force? (2)

A

PD - the transfer of electrical energy to other types of energy
EMF - the transfer of other types of energy to electrical energy

4
Q

What is 1 volt equal to?

A

1 joule per coulomb

5
Q

How is voltage calculated?

A

V (V) = W (J) / Q (C)

6
Q

How is the energy transfer for electrons and other charged particles calculated?

A

eV = 1/2 mv^2

7
Q

How is resistance calculated?

A

R = V / I

8
Q

What is Ohm’s law?

A

The current in an ohmic conductor is proportional to the voltage across it, provided that the temperature and other physical conditions are kept constant

9
Q

What is electrical resistance? (2)

A

The interference of metal atoms with the motion of electrons

The amount of volts per amp

10
Q

How does temperature affect resistance? (2)

A

As temperature increases, atoms vibrate faster

The likelihood of them impeding electron flow increases meaning resistance increases

11
Q
```I-V Characteristics:
Fixed Resistor (4)```
A

Straight line through (0,0)
Voltage is directly proportional to current
Obeys Ohm’s law
Resistance is constant

12
Q
```I-V Characteristics:
Filament Bulb (4)```
A

For the same change in voltage, current increases less as voltage increases
Voltage is not proportional to current
Does not obey Ohm’s law
Resistance increases as PD increases

13
Q

I-V Characteristics:

LED

A

Before the activation PD (0.7 - 1.5) there is infinite resistance so no current flows
After the activation PD resistance decreases rapidly
A large current flows with a small PD
Does not obey Ohm’s law

14
Q

I-V Characteristics:

Thermistor (4)

A

For the same increase in PD, current increases at an increasing rate
As current increases, temperature increases causing resistance to fall
Resistance decreases with increasing PD
Does not obey Ohm’s law

15
Q

How does the resistance of an LDR change with light intensity? (3)

A

Resistance decreases as light intensity increases
Photons of light hit a cadmium sulphide track, giving the electrons enough energy to jump into the conduction band
Approximately 1 mega ohm to 500 ohms resistance

16
Q

What is the equation for the resistivity of a metal?

A

Resitivity (ohm metres) = AR / L
A = cross sectional area (m^2)
R = resistance (ohm)
L = length (m)

17
Q

What is resistivity? (2)

A

An electrical property of a material that affects its resistance
Resistivity is constant at a constant temperature

18
Q

How does the resistance of a thermistor change with temperature?

A

As temperature increases, resistance decreases

19
Q

What is power?

A

The rate of doing work

20
Q

How is power calculated? (2)

A

P (W) = V (V) x I (A)
Or
Power = energy / time

21
Q

What is 1 watt equivalent to?

A

1 joule per second

22
Q

How is energy transfer calculated?

A

Energy transfer = voltage x current x time

23
Q

How is energy calculated? (2)

A

Energy (J) = Power (W) x Time (s)

Energy (kWh) = Power (kW) x Time (hr)

24
Q

What is 1kWh? (2)

A

The energy transferred by a device working at 1kW for 1 hour

1kWh = 3.6 MJ