# 4.2 Energy, Power and Resistance Flashcards

What is potential difference? (2)

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

What is electromotive force?

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

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

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

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

What is 1 volt equal to?

1 joule per coulomb

How is voltage calculated?

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

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

eV = 1/2 mv^2

How is resistance calculated?

R = V / I

What is Ohm’s law?

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

What is electrical resistance? (2)

The interference of metal atoms with the motion of electrons

The amount of volts per amp

How does temperature affect resistance? (2)

As temperature increases, atoms vibrate faster

The likelihood of them impeding electron flow increases meaning resistance increases

I-V Characteristics: Fixed Resistor (4)

Straight line through (0,0)

Voltage is directly proportional to current

Obeys Ohm’s law

Resistance is constant

I-V Characteristics: Filament Bulb (4)

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

I-V Characteristics:

LED

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

I-V Characteristics:

Thermistor (4)

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

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

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