Module 4: Electricity

Question 1

Electric force

Answer 1

The force responsible for binding nuclei and electrons to form atoms, binding atoms to form molecules, and binding molecules to form bulk materials

Question 2

What does electrical force act upon?

Answer 2

Charged objects

Question 3

Unit for charge

Answer 3

C coulombs

Question 4

Smallest nonzero charge an object can have

Answer 4

qe

Question 5

Value of qe

Answer 5

1.6 x 10^-19 C

Question 6

Describe charging by friction

Answer 6

Electrons are transferred from one insulator to another when they are rubbed together

Question 7

Conductor

Answer 7

A material where charge can move freely

Question 8

Insulator

Answer 8

A material where charge cannot move freely

Question 9

Two examples of conductors

Answer 9

Metals

Salty water

Question 10

Four examples of insulators

Answer 10

Plastics
Oil
Glass
Undissolved salt

Question 11

Do conductors have a high or low resistivities?

Answer 11

Low

Question 12

Do insulators have high or low resistance?

Answer 12

High

Question 13

Polarisation

Answer 13

The separation of charges in a neutral object

Question 14

In which materials does polarisation occur to a larger extent?

Answer 14

Conductors

Question 15

|q|

Answer 15

Absolute value of charge

Question 16

In which direction does an electric field go?

Answer 16

Positive to negative

Question 17

Function of a battery

Answer 17

Kees constant potential difference across terminals

Question 18

How can we increase the capacitance? (3)

Answer 18

Decrease distance between plates
Increase size of plates
Add a capacitor in parallel

Question 19

Relative permittivity

Answer 19

Range between 1-100

Can find actually permittivity by multiplying this with the permittivity of a vaccum

Question 20

What circuit component does a cell membrane (and fluid around it) act like?

Answer 20

Capacitor

Membrane is insulator between two ‘plates’ of salty water

Question 21

How does capacitance relate to our reaction times?

Answer 21

The capacitance of nerve cell membranes determines how fast you can think

The smaller the capacitance, the faster the reaction time

Question 22

Which has a larger capacitance: capacitors in series or parallel?

Answer 22

Parallel

Question 23

Which has a larger resistance: resistors in series or in parallel?

Answer 23

Series

Current can split through two resistors in parallel

Question 24

Conventional current

Answer 24

The current in the direction of positive charge flow

Opposite direction to conduction (movement of electrons)

Question 25

What property determines a specific objects resistance?

Answer 25

It’s geometry (additional to the materials resistance)

Question 26

Kirchoffs law #1

Answer 26

The sum of potential charges around a loop is zero Due to conservation of energy

Question 27

Kircchoffs law #2

Answer 27

The current flowing into a junction is the same as the current flowing out Due to conservation of charge

Question 28

What happens to electrical energy as it passes through a resistor?

Answer 28

They lose energy- bashing into the metal atoms of the resistor This energy is converted into heat

Question 29

Why don’t electrons slow down as they travel ‘through’ the battery, like they do in a resistor?

Answer 29

The battery provides chemical energy- which is converted into electrical energy in the electrons

Question 30

If potential is decreased in the direction of current flow, what happens to the power?

Answer 30

Dissipates

Question 31

How do we increase the potential in the direction of current flow?

Answer 31

Power input

Question 32

If two lights are connected in series, will they be as bright as one?

Answer 32

No- resistance is doubled (and voltage stays the same) so the current is halved Power is halved

Question 33

What happens to the brightness if we add two lightbulbs in parallel?

Answer 33

Same brightness- resistance is halved, so current is doubled Power is doubled through two lights- so each is the same as before

Question 34

Four factors determining how dangerous an electric shock can be

Answer 34

Amount of current (not voltage) Path taken by current (through body) Duration of shock Frequency (DC more dangerous than AC)

Question 35

Why is most electrical interference (e.g. defibrillator) done through the skin?

Answer 35

Because skin provides a large resistance that prevents current through the body from being too large

Question 36

RC circuit

Answer 36

Resistor and capacitor in series

Question 37

When does the charging of a capacitor finish?

Answer 37

When the voltage across the capacitor = voltage across the resistor

Question 38

What happens to the rate of charge in a capacitor when discharging? What is this called?

Answer 38

Decreases as current approaches zero Exponential decay

Question 39

RC

Answer 39

Time constant/ RC constant Time taken for charge to drop to 37% of previous value

Question 40

For a circuit that quickly reaches equilibrium, will the time constant be small or large?

Answer 40

Small- small resistance and capacitance