Section 6 - Electricity

Question 1

Define current

Answer 1

Rate of flow of charge

Question 2

What is the unit of current?

Answer 2

A - Ampere

Question 3

What is the unit of charge?

Answer 3

C - Coulomb

Question 4

Define coulomb

Answer 4

The amount of charge that passes in 1 second of the current is 1 ampere

Question 5

How do you measure current, and how do you connect the component?

Answer 5

With an ammeter in series

Question 6

Define potential difference

Answer 6

Work done per unit charge moved

Question 7

How do you measure voltage, and how do you connect the component?

Answer 7

With a voltmeter in parallel

Question 8

Define a volt

Answer 8

When one joule of energy is moving 1 coulomb of charge through a component

Question 9

Define resistance

Answer 9

A potential difference of 1 volt making a current of 1 amp generates 1 Ohm, R = V / I

Question 10

State Ohm’s law

Answer 10

Provided the physical conditions are kept constant, the current through an ohmic conductor is directly proportional to the p.d across it

Question 11

What do I/V graphs show in terms of resistance?

Answer 11

How it varies

Question 12

On an I/V graph for a resistor, what does a steep and shallow gradient represent?

Answer 12

Steep means low resistance

Shallow means steep resistance

Question 13

On an V/I graph for a resistor, what does a steep and shallow gradient represent?

Answer 13

Steep means high resistance

Shallow means low resistance

Question 14

Describe the curve for a filament lamp on an I/V and V/I graph

Answer 14

I/V - Starts shallow but gets steeper curve. Only touches the origin type cubic
V/I - Starts steep and gets shallower. Point of inflexion type cubic as stays at origin for a bit

Question 15

What is a filament?

Answer 15

A coiled up length of wire

Question 16

State an application for semi conductors

Answer 16

Sensors, diodes and thermistors

Question 17

Why are semiconductors good sensors?

Answer 17

When energy is supplied, more charge carriers are released

Question 18

What does the resistance of a thermistor depend on?

Answer 18

Temperature

Question 19

What happens as the temperature of a thermistor increases?

Answer 19

Resistance decreases

Question 20

Describe the resistance-temperature graph for a thermistor

Answer 20

Top left to bottom right inward curve

Question 21

Describe the I/V and V/I graph for a thermistor

Answer 21

I/V - Starts steep and gets shallower
V/I - Starts shallow and gets steeper
OPPOSITE TO FILAMENT LAMP

Question 22

What are diodes designed to do?

Answer 22

Let current flow in 1 direction

Question 23

Describe the I/V and V/I graph for a diode

Answer 23

I/V - At 0 until about 0.6V then sharp spike

V/I - Sharp increase and then steady upward sloping line

Question 24

What 3 things determine resistance?

Answer 24

Length - Longer the wire, the lower the current
Area - The wider the wire, the larger the current
Resistivity - Depends on material

Question 25

Define resistivity

Answer 25

The resistance of a 1m wire with a 1m^2 of cross sectional area

Question 26

What is the unit of resistivity?

Answer 26

Ohm meters

Question 27

Describe the process to find the resistivity of a wire

Answer 27

- Use micrometer to measure diameter in multiple places - Take an average and find area of wire - Test wire should be clamped where the ruler reads 0 - Attach the flying lead to the clamped wire and record the length of the wire - Record the voltmeter and ammeter reading and calculate resistance - Repeat and draw a graph. Multiply the area by the gradient = resistivity

Question 28

State uses of superconductors

Answer 28

- Power cables transmit electricity with no loss of power - Strong electromagnets don't need a constant power source - Electronic circuits work really fast

Question 29

Define power

Answer 29

The rate of transfer of energy

Question 30

State the extra power equations you need to know

Answer 30

``` P = I^2R P = V^2 / R ```

Question 31

State the energy equation you need to know

Answer 31

E = IVt

Question 32

Where does resistance come from?

Answer 32

Electrons colliding with atoms and losing energy to other forms

Question 33

What makes electrons move in a battery?

Answer 33

Chemical energy

Question 34

What is emf?

Answer 34

The amount of electrical energy the battery produces for each coulomb of charge

Question 35

What is the terminal p.d?

Answer 35

The energy transferred when 1 coulomb of charge flows through the load resistance

Question 36

What are lost volts?

Answer 36

Energy wasted per coulomb overcoming the internal resistance

Question 37

What is the terminal p.d if there is no internal resistance?

Answer 37

The same as the emf

Question 38

How can you calculate the total emf in a series circuit?

Answer 38

By adding the their individual emfs

Question 39

How can you calculate the total emf in a parallel circuit?

Answer 39

The total emf of the cells is the same size as the emf of each of the individual cells

Question 40

Does charge get used up in a circuit?

Answer 40

No

Question 41

State Kirchhoff's first law

Answer 41

Total current entering a junction = total current leaving it

Question 42

State Kirchhoff's second law

Answer 42

Total emf around a series circuit = sum of pds across each component

Question 43

What does a potential divider do?

Answer 43

It splits the pd across the voltage source into a ratio of resistances

Question 44

What is the use for a potential divider?

Answer 44

Supply a pd between 0 and the pd across the voltage source

Question 45

What is a use for a variable resistor?

Answer 45

To vary voltage

Question 46

What is the use of a potentiometer?

Answer 46

Using a variable resistor to give a variable voltage