efficiency and reducing wastes

Question 1

what determines if something is more efficient?

Answer 1

less energy that is wasted

Question 2

how do you work out efficiency?

Answer 2

useful power output / total power input

Question 3

example: a blender is 70% efficient and has a total input of 600w, what is the useful output power?

Answer 3

0.7 x 600 = 420 w

Question 4

what is the exception to the rule that no device is 100% efficient?

Answer 4

electric heaters because all of the electrostatic energy goes towards the useful thermal energy stores

Question 5

how can you reduce the amount of energy wasted?

Answer 5

lubrication and thermal insulation

Question 6

how does lubrication reduce energy wasted?

Answer 6

it reduces frictional forces

Question 7

what happens if frictional forces aren’t reduced?

Answer 7

the object can be transferred thermal energy stores that are useless

Question 8

how does insulation reduce the amount of energy wasted?

Answer 8

it reduces the rate of energy transfer by heating

Question 9

why would you want to prevent energy losses in things like a house?

Answer 9

because you want to create a warm environment and without insulation the heat would escape outside

Question 10

what are the ways to prevent energy loss through heating?

Answer 10

having thick walls that are made from low thermal conductivity materials or use thermal insulation

Question 11

what can cavity wall insulation do?

Answer 11

reduce energy transfer by convection in the wall cavity

Question 12

what does loft insulation do?

Answer 12

reduce convection currents being created in lofts

Question 13

what are other examples of thermal insulation?

Answer 13

double-glazed windows (work in the same way as cavity walls) and draught excluders

Question 14

how can you investigate the effectiveness of materials as thermal insulators?

Answer 14

using different materials to surround boiling water and record how much the temperature changes to evaluate which material is the best insulator