4.2 - Electricity - Energy, Power and Resistance

Question 1

What is potential difference (V)

Answer 1

It is used to measure the work done by charge carriers, which lose energy as they pass through the components in a circuit,

Question 2

What is potential difference (V) defined as

Answer 2

The energy transferred from electrical energy to other forms per unit charge

Question 3

What equation contains potential difference, energy and charge

Answer 3

V = W/Q

Question 4

What is 1 volt defined as

Answer 4

1 joule of energy transferred per coulomb

Question 5

What is electromotive force (e.m.f)

Answer 5

Is it the work done to charge carries, when they gain energy as they pass through a cell or power supply

Question 6

What is the difference between voltage and emf

Answer 6

Voltage is energy transferred per coulomb across a load resistance.
Emf is the total amount of work done by the battery per coulomb

Question 7

Is the kinetic energy of an electron is multiplied by its charge multiplied by the voltage

Answer 7

Yes, Energy transferred = eV = 1/2 x m x v^2

Question 8

What is the equation for resistance

Answer 8

R = V/I

Question 9

What is resistance defined as

Answer 9

The potential difference across the component, divided by the current in the component.

Question 10

What is resistance

Answer 10

How difficult it is for current to flow through an appliance.

Question 11

What is the definition of 1 Ohm

Answer 11

When a resistor is subject to a voltage of 1V and allows a current of 1A through

Question 12

What is an ohmic conductor

Answer 12

A conductor that obeys Ohm’s law

Question 13

What is Ohm’s law

Answer 13

The current through an ohmic conductor is directly proportional to the potential difference across it. (resistance doesn’t vary with voltage or current)
(only true if constant temperature)

Question 14

What graph represents an ohmic conductor

Answer 14

A line that has a constant gradient (straight line) and passes through the origin

Question 15

On a I V graph what shows a higher resistance

Answer 15

A smaller gradient means a higher resistance

Question 16

What graph represents a non ohmic conductor

Answer 16

Scoops at the bottom left going up through the origin then begins to curve over.

Question 17

What is an example of a non ohmic conductor

Answer 17

Filament lamp where as current increases so does resistance

Question 18

What graph represents a diode

Answer 18

Flat when the voltage is negative or 0 then has a curved increase (not present in negative current as in diode current only flows in one direction)

Question 19

What is a light dependent resistor (LDR)

Answer 19

A semiconductor that is sensitive to light, as light intensity increases the resistance decreases (brighter = more resistance)

Question 20

What is a thermistor

Answer 20

As the temperature increases the resistance decreases (thermistors that work this way are called negative temperature coeficcient)

Question 21

What is resistivity

Answer 21

The resistivity of a metal shows how east or difficulty it is for current to flow in the material (at a specific temperature)

Question 22

What is the resistivity equation

Answer 22

p = RxA / L
( resistivity = resistance x cross sectional area / length )

Question 23

What is the experiment to determine resistivity of a metal

Answer 23

Take a wire use a micrometeor to measure diameter then calculate area. Vary length in wire and record voltage and current. Use R=V/I to work out resistance. Plot a graph of resistance against length. Gradient = resistivity / area. resistivity = gradient x area

Question 24

What is power

Answer 24

Rate of energy transfer

Question 25

What is the equation for power

Answer 25

P = V x I

Question 26

Why are kilo watt hours (kWh) used

Answer 26

As joules and watts are both too small so to be more practical and make the numbers smaller for people electrical companies use kWh

Question 27

Equation to find cost of electricity

Answer 27

Total cost = units x price