4.1.2.1 Energy Transfers in a System

Question 1

What is the principle of conservation of energy?

Answer 1

• Energy cannot be created or destroyed
• It can only be transferred from one store to another usefully, stored or dissipated
• Energy in = Energy out

Question 2

What is the input and output of energy in a closed system?

Answer 2

• In a closed system the total energy input into the system is equal to the total energy output
• This is known as the Principle of Conservation of Energy
• Only some of the energy output is useful, the rest of the energy is dissipated as wasted energy (usually into thermal store)

Question 3

When is energy dissipated and give an example:

Answer 3

• Energy is dissipated in all system changes so that is stored in less useful ways (often described as being wasted e.g. Friction can result in energy being dissipated as thermal energy
  
  • This can be reduced with lubrication

Question 4

Can thermal energy be dissipated into the surroundings? if so how can it be reduced?

Answer 4

Thermal energy can also be dissipated to the surroundings, but this can be reduced with the use of thermal insulation

Question 5

E transfers (pathways):

Answer 5

• Mechanically – ask yourself is a force being applied over a distance
• Electrically
• By heating
• By radiation

Question 6

Give two ways of reducing unwanted energy transfers:

Answer 6

• through lubrication

- through the use of thermal insulation

Question 7

The higher the thermal conductivity of a metal…

Answer 7

the higher the amount of heat transferred

Question 8

What is the rate of cooling of a building affected by?

Answer 8

The rate of cool of a building affected by the thickness and thermal conductivity of its walls