Science - Energy Transfer Unit

Question 1

What is the difference between temperature and heat?

Answer 1

• Heat is energy.
• When an object gains heat energy, its particles start to move more.
• Temperature is a measurement of how hot an object is.
• The more particles that are moving, and the faster they move, the more heat energy the object has.

Question 2

What is the difference between temperature and energy?

Answer 2

The heat an object contains is the amount of its thermal energy, measured in Joules or J.
The temperature of an object is to do with how hot or cold it is, measured by a thermometer in degrees Celsius.

Question 3

The energy that is needed to increase the temperature of a material depends on:

Answer 3

• Mass of material
• Required temperature rise
• What the material is made of

Question 4

Why does heat transfer happen?

Answer 4

Heat is a type of energy called thermal energy.
During heat transfer, thermal energy always moves in the same direction
Heat energy is only transferred when there is a temperature difference from a warmer area to a cooler area.

Question 5

What is conduction?

Answer 5

Conduction is the method of heat transfer in solids but not liquids and gases. This is because solid particles are very close together but the particles in liquids and gases are further.
The best type of solid conductors are metals.

Question 6

Why are metals the best conductors?

Answer 6

The outer electrons of metal atoms are not attached to any particular atom. They are free to move between the atoms. This makes them really good at transferring energy from one atom to the next.

Question 7

How does heat move through solids?

Answer 7

Conduction

Question 8

What happens to the particles when they are heated?

Answer 8

Vibrate Faster

Question 9

How is the heat passed through the solid?

Answer 9

Vibrations are passed along

Question 10

Which metal is the best conductor?

Answer 10

Copper

Question 11

Why does air not conduct heat well?

Answer 11

Particles are far apart

Question 12

What is a convection current?

Answer 12

Thermal energy is transferred from hot places to cold places by convection. The hot air rises and the cold air falls. This is a convection current.

Question 13

What happens when a fluid is heated?

Answer 13

The heated fluid particles gain energy, so they move about more and spread out. The same number of particles now take up more space, so the fluid has become less dense.

Question 14

What is a convection current?

Answer 14

The steady flow between the warm and cool sections of a fluid, such as air or water, is called a convection current.

Question 15

How does convection work?

Answer 15

Warmer regions of a fluid are less dense than cooler regions of the same fluid. The warmer regions will rise because they are less dense. The cooler regions will sink as they are more dense.

Question 16

How does heat energy travel from the Sun to the Earth?

Answer 16

There are no particles between the Sun and the Earth so the heat cannot travel by conduction or by convection.

The heat travels to Earth by infrared waves. They are similar to light waves and are able to travel through empty space.

Question 17

What is the best emitters of radiation and the worst emitters of radiation?

Answer 17

Best: Matt Black
Worse: Shiny colours (Silver, White)

Question 18

What are the best absorbers of radiation and the worst absorbers of radiation?

Answer 18

Matt black surfaces are the best absorbers of radiation.
Shiny surfaces are the worst absorbers because they reflect most of the radiation away.

Question 19

List 3 things infrared radiation is used for

Answer 19

Any 3 from:
- Detect signs of breast cancer up to 2 years earlier than previous methods.
- Develop remote controls
- Night vision used by the police and military
- Learn more about our universe
- Find people in fires
- Read the dead sea scrolls (Early Abrahamic texts)

Question 20

Complete the sentences:
- Houses in hot countries are often painted white because….
- Solar panels on the roof of a house are painted black….
- Electric fires often have a shiny metal sheet behind the heating element…..
- A car radiator is usually painted in black because…
- A matt surface absorbs infrared radiation…..

Answer 20

1- Light surfaces are poor absorbers of radiation
2- So they absorb as much solar radiation as possible
3- Because light shiny surfaces are good reflectors of infrared radiation
4- It will radiate infrared energy more quickly
5- Better than a shiny surface

Question 21

Complete the sentences:
Heat energy gets to Earth from the sun by…
Matte black materials are…
These houses in Greece are white because…

Answer 21

1- Infrared waves
2- The best absorbers of radiation and the best emitters of radiation
3- White is not a good emitter of radiation

Question 22

Explain how evaporation happens:

Answer 22

As the particles vibrate / move there are many collisions between them. This causes some particles to have more energy and other particles to have less energy. We say there is a “varying distribution of energies”.
Some of the particles will gain enough kinetic energy to escape from the top surface of the liquid. This leaves the particles that have less kinetic energy behind in the liquid resulting in the average kinetic energy and speed of the remaining particles to decrease. This decrease in the average energy of the particles results in a decrease in the
temperature of the liquid and a cooling effect is observed.

Question 23

Particles collide with each other —–> Distribution of Energies ——> Some particles l____ k_____ e____, Some particles g____ k____ e_____ These particles ______ _____ and _____ _____ _____ _____. These particles move _____. The remaining liquid c___ d____ and these particles e_____ and e______/

Answer 23

Particles collide with each other —–> Distribution of Energies ——> Some particles lose kinetic energy, Some particles gain kinetic energy, These particles move slower and remain in the liquid. These particles move faster. The remaining liquid cools down and these particles escape and evaporate.