1.2 Conservation and Dissipation of Energy Flashcards

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1
Q

state the law of energy conservation.

A

energy cannot be created or destroyed (it can only be transferred into different forms).

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2
Q

state any changes in the total energy of a ball that is kicked, assuming that no external forces act.

A

the total energy of the system remains constant due to the conservation of energy.

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3
Q

describe the energy changes that occur in a filament light-bulb.

A
  • electrical energy is transferred into light and heat energy
  • light is a useful energy form, heat is waste energy
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3
Q

state two equations to calculate efficiency.

A

useful output energy transfer/total input energy transfer
useful power output/total power output

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4
Q

how can the efficiency of a system by increased?

A
  1. reducing waste output (by lubrication, thermal insulation etc)
  2. recycling waste output (e.g. recycling thermal waste energy as input energy)
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4
Q

what is waste energy?

A

the energy that is not used by the device for its desired purpose.

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4
Q

state the consequences for energy transfer of a material with a high thermal conductivity.

A

the rate of energy transfer through the material is higher than for a material with a lower thermal conductivity.

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5
Q

do double-glazed windows have a higher or lower thermal conductivity than single-glazed windows?

A

lower, meaning less energy transfers through them.

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6
Q

what key factors affect the rate of cooling of a building?

A
  • the thickness of the walls
  • the thermal conductivity of the walls
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7
Q

state three methods of reducing heat loss in a building.

A
  1. double glazing
  2. loft and wall insulation
  3. thicker walls
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8
Q

how can the efficiency of a mechanical machine with moving parts be improved?

A

lubricate any moving parts to reduce the friction and therefore energy loss due to heating.

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9
Q

how can the efficiency of a radiator be improved?

A

installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed into the walls.

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10
Q

how can the efficiency of boiling water in a pan be improved?

A

by placing a lid on the pan to reduce the heat loss from the top.

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