1.2 Conservation and dissipation of energy

Question 1

1.2.1 - energy transfers in a system

Law: conservation of energy

Answer 1

Energy can be transferred usefully, stored, dissipated. Cannot be created or destroyed

Question 2

1.2.1 - energy transfers in a system

Energy transfers in a closed system

Answer 2

can be a transfer of energy, but not mass
no change to the total energy in the system

Question 3

1.2.1 - energy transfers in a system

Sankey diagram

Answer 3

• the thicker the line/arrow, the greater amount of energy involved
• shows useful energy and wasted energy

Question 4

1.2.1 - energy transfers in a system

Reducing unwanted energy transfers

Answer 4

Lubrication:
* friction = unwanted heat. lubricating reduces friction

Thermal insulation:
* the higher the thermal conductivity, the quicker heat is transferred through the material.
* insulation uses materials with low conductivity, like fibreglass in the loat, double glazed windows, foam in wall cavities.

Question 5

1.2.2 Efficiency

Formula for efficiency

Answer 5

Efficiency = useful output energy transfer / total input energy transfer

Efficiency = useful power output / total power input

efficiency = (useful output/ total input) x 100