P2 Electricity

Question 1

What is alternating current?

Answer 1

Electric current in a circuit that repeatedly changes direction

Question 2

What is direct current?

Answer 2

Electric current in a circuit that flows in one direction only

Question 3

What is power?

Answer 3

The energy transformed or transferred per second

Question 4

What is the unit for power?

Answer 4

Watts, W

Question 5

What is efficiency?

Answer 5

Useful energy transferred by a device / total energy supplied to a device

Question 6

What is potential difference?

Answer 6

A measure of the work done or energy transferred between 2 points in an electrical circuit

Question 7

What is the unit for potential difference?

Answer 7

Volts, V

Question 8

What is the national grid?

Answer 8

The network of cables and transformers used to transfer electricity from electricity producers to electricity consumers

Question 9

What is the unit for energy?

Answer 9

Joules, J

Question 10

What are the 3 equations to calculate power?

Answer 10

1. Power = Energy / Time (P = E / T) - PET
2. Power = Current x Voltage (P = I x V) - Penguins in Vegas
3. Power = Current^2 x Resistance (P = I^2 x R) - Penguins in a square room

Question 11

What are the 2 equations to calculate energy?

Answer 11

1. Energy = Power x Time (E = P x T)
2. Energy = Charge x Voltage (E = Q x V) - Every Queen Vacuums

Question 12

What are the 2 equations to calculate efficiency?

Answer 12

1. (useful energy out / total energy in) x 100
2. (useful power out / total power in) x 100

Question 13

What colour is the live wire?

Answer 13

Brown

Question 14

What is the function of the live wire?

Answer 14

Carries a current that alternates between negative and positive voltage - current flows in through

Question 15

What colour is the earth wire?

Answer 15

Green/yellow

Question 16

What is the function of the earth wire?

Answer 16

A safety feature that is needed to earth electrical appliances with metal casing. This makes it safer to touch an appliance if it develops a fault - only has current if there is a fault

Question 17

What is the function of the neutral wire?

Answer 17

Completes the circuit. Kept at 0 voltage by the electricity company - current flows out through

Question 18

What colour is the neutral wire?

Answer 18

Blue

Question 19

What is the function of the fuse in a plug?

Answer 19

Can melt (blow) if too much current flows through - breaks the circuit

Question 20

What type of supply is mains electricity?

Answer 20

a.c. supply

Question 21

What is the voltage of mains electricity?

Answer 21

230V

Question 22

What is the frequency of mains electricity?

Answer 22

50Hz

Question 23

What does the frequency of mains electricity mean (50Hz)?

Answer 23

That it changes direction and back again 50 times a second (analogue signal graph)

Question 24

What does directly proportional mean?

Answer 24

Double one, doubles the other

Question 25

What does inversely proportional mean?

Answer 25

Double one, halves the other

Question 26

What does a diode do?

Answer 26

Only lets current flow one direction - very high resistance in the 'wrong direction'

Question 27

What is current measured in?

Answer 27

Amps, A

Question 28

What is charge measured in?

Answer 28

Coulombs, C

Question 29

What is potential difference?

Answer 29

Difference in energy between 2 points

Question 30

What is the function of a thermistor?

Answer 30

Changes resistance with temperature - higher temp = lower resistance

Question 31

What is the function of a variable resistor?

Answer 31

We can manually change the resistance

Question 32

What is the function of a fixed value resistor?

Answer 32

Always has the same resistance value

Question 33

What is resistance?

Answer 33

How hard it is for current to flow

Question 34

What are the 2 types of circuit?

Answer 34

Series and parallel

Question 35

Explain current in a series circuit:

Answer 35

Current same at every point in a series circuit

Question 36

Explain current in a parallel circuit:

Answer 36

Total current in a parallel circuit = sum of currents through the separate components

Question 37

Explain p.d. in a series circuit:

Answer 37

Total p.d. of power supply is shared between the components

Question 38

Explain p.d. in a parallel circuit:

Answer 38

p.d across each component is the same

Question 39

Explain resistance in a series circuit:

Answer 39

More resistors, greater the resistance. Total resistance of 2 components = sum of resistance of each component (R^total = R^1 + R^2)

Question 40

Explain resistance in a parallel circuit:

Answer 40

More resistors, lower resistance. Total resistance of 2 resistors is less than resistance of smallest individual resistor

Question 41

What is the equation for charge?

Answer 41

Charge = current x time (Q = I x T)- QUIT

Question 42

What is the equation for potential difference?

Answer 42

p.d. = current x resistance (V = I x R) - Very Important Rabbit

Question 43

What is the equation for power?

Answer 43

Power = p.d. x current (P = I x V) - Penguins In Vegas

Question 44

What is the equation for energy transferred?

Answer 44

Energy transferred = power x time (E = P x T)

Question 45

What is electric current?

Answer 45

Flow of electric charge

Question 46

What is resistance caused by?

Answer 46

Anything which opposes the flow of electric charge

Question 47

What is charge?

Answer 47

Anything charged which is able to move within a circuit - electrons or ions

Question 48

What is a series circuit?

Answer 48

A circuit with only one route for charge to take

Question 49

What is a parallel circuit?

Answer 49

A circuit with more than one route for charge to take

Question 50

Describe the V/I graph of a filament lamp:

Answer 50

Resistance is not constant - as temp increases, resistance increases as ions vibrate more increasing collisions with electrons

Question 51

Describe the V/I graph of a fixed resistor:

Answer 51

Resistance is constant. Current and p.d. are directly proportional

Question 52

Describe the V/I graph of a diode/LED:

Answer 52

Current flows one-way. High resistance in reverse direction

Question 53

What is the function of a step-up transformer?

Answer 53

Increases p.d. for transmisson across power cables - less current, less heat lost

Question 54

What is the function of a step-down transformer?

Answer 54

Reduces the p.d. from the cables to 230V for use by consumers

Question 55

What power supply does batteries/cells use?

Answer 55

d.c. supply

Question 56

Where do electric fields exist?

Answer 56

Around all objects

Question 57

Electric fields - what does it mean if field lines are closer together?

Answer 57

Pulling force is stronger

Question 58

Where do field lines point?

Answer 58

Positive to negative charge

Question 59

What is the equation for density?

Answer 59

Density = mass (kg) / volume (m^3)

Question 60

What is density?

Answer 60

The mass of a substance per unit volume

Question 61

Are smaller objects more/less dense?

Answer 61

More dense

Question 62

What happens when 2 insulators are rubbed together?

Answer 62

They become charged

Question 63

What does friction force cause?

Answer 63

Electrons to be transferred between insulators

Question 64

Is the total no. of protons/electrons constant or alternating?

Answer 64

Constant

Question 65

Do oppositely charged objects attract/repel?

Answer 65

Attract

Question 66

Do objects with the same charge attract/repel?

Answer 66

Repel

Question 67

What is charging by induction?

Answer 67

When a negative object is moved towards a negative object, electrons are repelled to the other side - closest surface becomes positively charged. Works same other way, leaving opposite surface negatively charged