Electricity (2)

Question 1

what is potential difference

Answer 1

energy transferred per charge passed

Question 2

what is the formula for Energy Transferred (J)

Answer 2

Charge Flow (C) x Potential Difference (V)

Question 3

What is the formula for Power (W)

Answer 3

Potential Difference (V) x Current (A)

Question 4

What does total energy transferred by an appliance depend on

Answer 4

how long an appliance is on for and its power

Question 5

What is the power of an appliance

Answer 5

the energy that it transfers per second (more energy transferred in a given time , the higher its power)

Question 6

What is energy transferred by electrical work (J)

Answer 6

Power (W) x Time (S)

Question 7

What is the National Grid

Answer 7

• A giant system of cables and transformers that covers the UK and connects power stations to consumers (anyone who is using electricity)
• The national grid transfers electrical power from power stations anywhere on the grid (the supply) to anywhere else on the grid where it’s needed (the demand – e.g. homes and industry)

Question 8

When can demand in electricity change

Answer 8

• when people get up in the morning
• when people get home from school / work
• when it starts to get dark / cold at night
• popular sporting event on tv (World Cup, The Olympics)

Question 9

How do stations prepare for massive changes in demand

Answer 9

• they often run at well below their maximum power output, so there’s spare capacity to cope with such high demand
• There are also lots of smaller power stations that can start up quickly that are kept in standby just in case

Question 10

How does national grid transmit huge amounts of power

Answer 10

• you need either a high potential difference or a high current
• Lots of energy can be lost as the wires heat up and energy is transferred to the thermal energy stores
• It’s much cheaper to boost the Potential Difference up really high ( 400,000 V ) and keep the current as low as possible

Question 11

What the problem in having a high current

Answer 11

• Lots of energy can be lost as the wires heat up and energy is transferred to the thermal energy stores

Question 12

How does the national grid get the potential difference to transmit 400,000 V worth of power

Answer 12

• Transformers ( that step the potential difference up )

- Big pylons with huge insulators

Question 13

what is the structure of a national grid

Answer 13

• Electricity travels from a power station to a step-up transformer ( steps up the potential difference ) to a massive pylon which can transmit the electricity from long distances to other pylons, the electricity then travels to a step-down transformer ( steps down the potential difference ) so it can eventually travel to the consumer