P1.3.1 Transferring Electrical Energy

Question 1

Describe the energy transfer system in the following devices:

1. Electrical devises, e.g. television
2. Batteries
3. Electrical generator, e.g. wind turbine
4. Potential energy, e.g. firing a bow and arrow

Answer 1

1. (television) electrical energy —> light, sound and wasted heat energy
2. (batteries) chemical energy —> electrical and wasted heat energy
3. (wind turbines) kinetic energy —> electrical and wasted heat energy
4. (firing a bow and arrow) elastic potential energy —> kinetic and wasted heat energy

Question 2

What two things does the amount of energy an appliance transfers depend on?

Answer 2

The amount of energy that an appliance transfers depends on how long the appliance is switched on and its power (how fast an appliance can transfer it).

Question 3

What formula is used to calculate the amount of energy transferred from the mains? Give the different units that can be used.

Answer 3

• Energy (J) = Power (W) x Time (s)
  1 Joule is the amount of energy transferred by a 1 Watt appliance in 1 second.
• Energy (kWh) = Power (kW) x Time (h)
  1 Kilowatt-Hour is the amount of energy transferred by a 1 Kilowatt appliance in 1 hour.

Question 4

What formulas are used to calculate the cost of mains electricity given the cost per kilowatt-hour?

Answer 4

• No. of Unit (kWh) used = Power (kW) x Time (hours)
• Cost = No of Units x Price per Unit
  i. e The number of units is basically the energy (remember E = P x T)

Question 5

If given two readings from an electricity meter and asked to calculate the total energy that’s been used over a particular time period, what do you do?
To calculate the cost of the energy used in that particular time period, what do you do?

Answer 5

Subtract the meter reading at the start of the time from the reading at the end to work out the total energy used over that time period in kWh.
To calculate the cost, just multiply the calculated energy used in this time period by the price per unit.

Question 6

What things might you need to consider when comparing the advantages and disadvantages of using different electrical appliances for a particular application?
(You might be given data to compare appliances, or might need to do calculations)

Answer 6

1. How much energy does each appliance use? So which one is better for the environment?
2. Which one is more efficient?
3. Which one is more cost-effective?
4. Which one is more practical?
5. Which one lasts longer?

Question 7

Consider the implications of instances when electricity is not available.

Answer 7

Most people have access to mains electricity in developed countries - without it, there would be a big impact on their particular standard of living:

1. Devices transform electricity into other useful types of energy, e.g lighting - this is useful, convenient and can help improve safety.
2. Refrigerators require electricity - they keep food fresh, slow growth of bacteria and keep vaccines cold.
3. Public health benefits from electricity, e.g. X-rays - with machines to diagnose and treat patients, life expectancy could be reduced and patients poorer.
4. Communications could be affected, without internet or phones - this makes it harder for people to keep in touch, or deliver news and information.