P1 - Energy Transfer

Question 1

What is potential energy?

Answer 1

Stored energy that is not being currently used

Question 2

What is the conservation of energy principle?

Answer 2

Energy can’t be created and destroyed but only transferred

Question 3

How do you calculate the energy efficiency of a device?

Answer 3

Efficiency = useful energy out / total energy in

Question 4

How do you calculate the power efficiency of a device?

Answer 4

Efficiency = useful power out / total power in

Question 5

What is the main cause of inefficiency of devices?

Answer 5

Energy is wasted as heat

Question 6

What device is usually 100% efficient?

Answer 6

Electric heaters (heat is not waste energy)

Question 7

What does “dissapated” mean?

Answer 7

When wasted energy (usually heat) becomes less concentrated (e.g. if heat spreads out)

Question 8

What are the 3 things you need to consider when buying an appliance?

Answer 8

Cost-effectiveness

Energy-efficiency

Whether the energy type needed is readily available

Question 9

What are heat exchangers?

Answer 9

A device that reduces the amount of heat energy lost by collecting some of it back

Question 10

Describe how heat exchangers work

Answer 10

A cool fluid is pumped through the escaping heat

The fluid temperature increases and can be used for heating

Question 11

What are the nine types of energy?

Answer 11

Electrical (flowing current)

Light

Sound

Kinetic (movement)

Nuclear potential (stored in nuclei of radioactive isotopes)

Thermal / heat

Gravitation potential

Elastic potential

Chemical potential (food, fuels etc.)

Question 12

What is a Sankey diagram?

Answer 12

A diagram that shows the input and output energies of a device and the device’s efficiency

Question 13

Describe how you would draw a Sankey diagram

Answer 13

Show the energy in going to the left with the number of joules labelled

The energy wasted in different ways are boxes that go downwards and end with a point, label the type of energy and amount (the box widths are proportional to the input energy) (different boxes for different types of energy)

The energy still travelling to the left ends in a point and it is labelled “useful” and then the type of energy and also the amount of energy

Question 14

What is the unit for energy used in homes?

Answer 14

Kilowatt-hours or kWh

Question 15

What is a kWh?

Answer 15

The amount of energy used by a 1kW appliance left on for 1 hour

Question 16

What is the formula that relates energy, time and power?

Answer 16

Energy = power * time

E = Pt

Question 17

What are the 2 formulas for calculating the cost of electricity?

Answer 17

Number of units used (kWh) = power (kW) * time (h)

Cost = no. of units * price per unit

Question 18

Give 4 ways that access to electricity affects standard of living

Answer 18

Many types of energy in the home are convenient and can increase safety (eg. lights)

Refrigerators keep food fresh and keep vaccines cold. Without this, the area’s population can be drastically effected

Electricity is needed in hospitals (X-rays, diagnosis etc.)

Communications require electricity

Question 18

What are the 2 usual waste energy types?

Answer 18

Heat

Sound