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BMAT val > Energy > Flashcards

Energy Flashcards

1
Q

What happens when a system changes?

A

There are changes in the way energy is stored

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2
Q

calculation of kinetic energy

A

kinetic energy (J) = 0.5 x mass (kg) x speed squared (m/s)

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3
Q

the calculation for the gravitational potential energy gained by raising an object above ground level

A

gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

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4
Q

the amount of elastic energy stored in a stretched or compressed spring can be found with the equation:

A

Ee (J) = 0.5 x spring constant (N/m) x extension ^2 (m)

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5
Q

the equation for power (energy transfer)

A

energy transferred/ time

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6
Q

equation for power (word done)

A

work done / time

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7
Q

what is wasted energy caused by?

A

unwanted energy transfer

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8
Q

How can unwanted transfers be reduced ?

A

lubrcation- reduces the friction that produces heat

tightening any loose parts - prevents unwanted vibration that wastes energy as sound

thermal insulation - resuces heat loss

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9
Q

What is thermal conductivity?

A

a measure of how well a material conducts energy when it is heated.

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10
Q

What does the rate of cooling depend on?

A

the thickness and thermal conductivity of the walls

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11
Q

what is special heat capacity?

A

the amount of energy required to raise the temperature of one kilogram of the substance by 1 degree celsius

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12
Q

what is internal energy?

A

the total kinetic and potential energy of all the particles that make up a system

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13
Q

what is the result of doing work on a system

A

it increases the energy stored in a system

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14
Q

How does heating change the energy in a system

A

by increasing the energy of the particles within it

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15
Q

as energy increases……

(what happens to the state and the temperture)

A

it will either increase the temperature or produce a change of state

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16
Q

the law of conservation of energy is ……

A

energy cannot be created or destroyed

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17
Q

the higher the thermal conductivity of a material

A

the higher the rate of energy transfer by conduction across the material.

18
Q

thin walls with hight thermal conductivity will conduct heat …..

A

the quickest and the building will cool down rapidly

19
Q

what are the three ways in which thermal energy can be transferred?

A

radiation, convection and conduction

20
Q

when does convection occur?

Describe it

A

when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less energy

The warmer fluid has lower density than the surrounding cooler fluid. So the warmer fluid moves upwards

The upwards movement of warmer fluid pushes cooler fluid out of the way, and the result is that cooler fluid moves around to take the place where the warmer fluid was.

As the warmer fluid rises, it gradually cools (by conduction of heat to the cooler fluid around it), becomes less dense, and tends to sink.

If the heat source continues to supply heat, a cycle of moving fluid, called a convection current, can develop within the fluid. Fluid nearest the heat source is continuously warmed, rises, and cools, while cooler fluid continuously moves to take its place next to the heat source.

21
Q

How is heat energy transferred from homes?

convection, conduction, radiation

A

convection - cold air can enter the house through gaps in the doors and windows and convection current can transfer heat energy in the loft to the roof tiles

conduction - through the walls, floor, roof and windows.

radiation - through the walls, roof and windows.

22
Q

materials with low thermal conductivity are _______ insulators

A

good

23
Q

what are the several ways in which you can reduce heat loss in homes

A

-carpets, curtains and draught excluders
- double glazing
- cavity wall insulation
- loft insulation

24
Q

how does double glazing reduce heat loss through windows?

A

double glazing has a vacuum in between the two panes of glass which means that there will be no conduction or convection

if double glazing has air, convection is minimised because there is little room for the air to move. Air is a poor conductor so there will be very little heat loss by conduction

25
Q

how is heat loss reduced through cavity wall insulation and loft insulation?

A

the insulating material is blown into the gap between the brick and the inside wall.

Insulating materials have low thermal conductivity and so this reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.

26
Q

What is a renewable energy resource?

A

one that is being (or can be) replenished as it is used.

27
Q

What are the main uses of energy resources?

A

transport, electricity generation and heating

28
Q

What is a non-renewable energy resource?

A

resources which will eventually run out

29
Q

what are the renewable energy resources? (7)

A

bio-fuel
wind
hydro-electricity
geothermal
Tidal
Solar
water waves.

30
Q

What are the non-renewable energy resources? (4)

A
  • Nuclear fuel
  • coal
  • oil
  • gas
31
Q

What are the factors that can affect the rate of conduction?

A

-temperature gradient (inc)
- decrease distance between objects
-surface area (more area in contact w heating surface inc)

32
Q

Describe the effect of temperature on the density of fluid. Describe how this causes fluid flow

A

increase in temperature = increases average speed of particles

separation between the particles increases and fluid expands = density decreaes

therefore hotter, less dense fluids will rise and be replaced by less dense colder fluid (convection current)

33
Q

Convection vs conudction

A

convection is more rapid method of heat conduction in fluid than conduction

covection cannot occur in solids due to the dixed nature of particles in relation to neighbouring particles

34
Q

What is thermal/infra-red radiation?

A
  • part of the electromagnetic spectrum
  • travels at the speed of light and does not require particles for energy transfer like conduction and convection
  • can transfer energy through a vacuum
  • radiation can be used to transfer energy to a far away object without heating the space in between
35
Q

What are the factors affecting the rate of absorption and emission of thermal radiation?

A

shiny objects = poor absorbers and emitters of thermal radiation
matt objects = good absorbers and emitters

  • the higher the temperature of the object, the greater the rate of thermal radiation emission
  • As an object emits radiation, the thermal energy
36
Q

What type of object is thermal radiation emitted by?

A

any object that is above the temperature of absolute zero

37
Q

What is the equation for specific heat capacity?

A

thermal energy/ mass x temperature change

38
Q

Why can’t heat travel in a vacuum by convection

A

does not contain particles.

39
Q

What does it mean when something is an insulator

A

a slow conductor, through which heat transfers by conduction relatively slowly.

40
Q

Describe conduction in different states

A

Gases are typically poorer conductors than liquids and solids. This is because the particles in a gas are far apart relative to their size. Collisions are not frequent enough to transfer kinetic energy between particles as quickly as in liquids and solids.

Liquids are typically poorer conductors than solids, because in a liquid the particles aren’t held tightly together, and it takes longer for kinetic energy to be transferred between particles.

41
Q

How does conduction work in metals?
Why are they good conductors?

A

In metals in the solid and liquid states, there are free electrons, which can move through the lattice of metal ions.

When part of a metal becomes hotter, not only the ions but also the free electrons gain kinetic energy. ions can only pass on kinetic energy relatively slowly, from one ion to its immediate neighbours and so on.

However, free electrons can transfer energy much faster, by moving through the lattice and colliding with ions and with each other. This is why metals are particularly good thermal conductors.

42
Q

What are the factors that affect conduction?

A

Rate of conduction higher for:
higher temperature difference

better thermal conductor

shorter distance

area of object surfaces in contact with connecting material = larger area

BMAT val (31 decks)

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