Efficiency

Question 1

what is the aim of energy efficiency

Answer 1

the aim of energy efficiency is to use less energy to provide the same service

Question 2

how can energy efficiency be increased in the homes of people using electrical appliances

Answer 2

reducing standby times of electrical appliances

Question 3

formula for calculating kinetic energy

Answer 3

KE = (1/2mass) x v^2

Question 4

what is wasted energy

Answer 4

wasted energy is the percentage of energy that isnt transferred to the energy stores of the device or is used to fulfil its function

Question 5

what is the wasted energy from a lightbulb and how is it wasted

Answer 5

• the wasted energy is thermal energy it gives off

- this energy is dispersed to the thermal energy stores of the surroundings

Question 6

how can heat loss be reduced in a house other than with cavity walls and why does this work

Answer 6

• double glazing windows
• because air is trapped between the windows so the heat has to be transferred through it
• but air is a lower thermal conductivity than solids
• so the heat from the house is lost at a slower rate

Question 7

what general method can be used to reduce energy loss

Answer 7

• cogeneration
• this consists of putting wasted energy (byproduct) of a machine to use by using it to power something else
• like transferring the heat given off by a generator to the thermal energy stores of water to heat it

Question 8

when is energy only useful

Answer 8

when it is transferred from one store to another useful store

Question 9

what can useful devices do

Answer 9

transfer energy from one store to a useful store

Question 10

how is some of the input energy from a store to a useful store usually lost as

Answer 10

it is lost or dissipated to the thermal energy stores of the surroundings

Question 11

how is efficiency decreased when work is done mechanically

Answer 11

• frictional forces have to be overcome
• like moving parts rubbing or air resistance
• the energy needed to overcome these frictional forces
• is transferred to the thermal energy stores of whatever is doing the work
• and the surroundings

Question 12

explain the energy transfers of a motor lifting a load

Answer 12

• energy is transferred electrically to the motor by the mains supply
• the motor transfers useful energy from its kinetic energy stores to the kinetic and gravitational potential energy stores of ghe load
• but it also transfers energy mechanically to the thermal energy stores of the moving parts
• and electrically to the thermal energy stores of the circuit
• the energy is dissipated, heating the surroundings

Question 13

what is the conservation of energy principle

Answer 13

total energy output = useful energy output + wasted energy

Question 14

what does the conservation of energy principle mean

Answer 14

the less energy that is wasted, the more efficient the device is said to be

Question 15

what is the formula for efficiency

Answer 15

• efficiency = useful energy transferred by device (J) / total energy supplied to device (J)
• multiply the calcluation by 100 to get the percentages

Question 16

is a fluorescent bulb more efficient than a filament bulb and if so, why

Answer 16

• the fluorescent light bulb is more efficient than an incandescent flashbulb
• as it uses less electrical energy