Energy Transfer

Question 0

How can the rate of heat transfer be sped up?

Answer 0

By increasing the difference in temperature between the object and its surroundings.

Question 1

What is infrared radiation?

Answer 1

The transfer of thermal energy by electromagnetic waves; no particles of matter are involved.

Question 2

How can the rate of heat transfer be slowed down?

Answer 2

By the use of insulation, which provides a barrier.

Question 3

What do dark matt surfaces do?

Answer 3

Absorb and emit more radiation than light shiny surfaces.

Question 4

What do light shiny surfaces do?

Answer 4

Reflect infrared radiation.

Question 5

What are the properties of particles in a solid?

Answer 5

They have the least energy.

They are not able to move but vibrate around a fixed point.

Question 6

What happens when a solid is heated?

Answer 6

It gives the particles enough energy to move around (but not very far apart) and it melts to become a liquid.

Question 7

What happens when a liquid is heated?

Answer 7

It gives the particles enough energy to move very quickly. They separate from each other and the liquid evaporates to become a gas.

Question 8

What is conduction?

Answer 8

The transfer of heat energy without the substance itself moving.

Question 9

How do metals conduct heat?

Answer 9

They are good conductors of heat.
As a metal becomes hotter, its tightly packed particles gain more kinetic energy and vibrate.
This energy is transferred to cooler parts of the metal by delocalised electrons, which move freely through the metal, colliding with particles and other electrons.

Question 10

How do non-metal solids conduct heat?

Answer 10

The particles can pass energy from one to the next by vibration.
However, the lack of free electrons makes most non-metals poor conductors.

Question 11

Why are gases bad conductors?

Answer 11

Because the particles are so far apart.

Question 12

What is convection?

Answer 12

The transfer of heat energy through movement. This occurs in liquids and gases and creates convection currents.

Question 13

How does convection occur?

Answer 13

In a liquid or gas the particles nearest to the heat source move faster and become further apart. This causes the substance to expand and become less dense than the colder parts.
The warm liquid or gas rises up and colder, denser liquid or gas moves into the space created where the warm liquid or gas was.

Question 14

What is condensation?

Answer 14

When a gas condenses to form a liquid, energy is released because the gas particles have more energy than those in a liquid. This can make the temperature increase.

Question 15

When can condensation occur?

Answer 15

When a warm gas comes into contact with a cold surface.
The surface needs to be cold enough to cool the particles so that they no longer have enough energy to move around quickly in a gas.
The colder the surface, the greater the rate of condensation.

Question 16

What is evaporation?

Answer 16

When a liquid’s particles have gained enough energy to escape the surface of the liquid and become a gas.

Question 17

How does a large surface area to volume ratio affect the rate of heat transfer?

Answer 17

It causes heat to be gained and lost quicker.

Question 18

How do different materials affect heat transfer?

Answer 18

Fur, feathers and human clothing are poor conductors and reduce heat loss. They also trap air, which is a bad conductor, and therefore reduce heat loss even more.

Question 19

How does sweating affect heat transfer?

Answer 19

As the moisture on our skin evaporates, it takes heat from its surroundings. So it increases heat loss and keeps us cool.

Question 20

How does the temperature difference between an object and its surroundings affect heat transfer?

Answer 20

The bigger the difference, the faster the object transfers heat.

Question 21

How does a vacuum flask keep hot drinks hot and cold drinks cold?

Answer 21

Shiny sides reflect infrared radiation and stop heat transfer.
Vacuum contains no particles so neither conduction nor convection can take place.
Screw top prevents evaporation from the surface and convection currents at the top.

Question 22

What is a U-value?

Answer 22

Indicates how effective a material is as an insulator because it shows how quickly heat energy can pass through.
The lower the U-value, the better the insulator.

Question 23

What is the payback time?

Answer 23

It tells us how long it would take to make, in efficiency savings, the amount it cost for the improvement (e.g. Loft insulation). It can be used to work out the cost effectiveness of different types of insulation as well as other improvements e.g. Solar panels.

Question 24

What is specific heat capacity?

Answer 24

The amount of energy needed to change the temperature of one kilogram of a substance by one degree Celsius.

Question 25

What can specific heat capacity be used for?

Answer 25

Deciding which materials to use in heating and cooling applications.

Question 26

How do solar panels work?

Answer 26

Water filled panels placed on a roof absorb heat from the Sun. This radiation energy warms the water. So the water in the panel stores a lot of heat energy, which can be used to heat buildings or provide domestic hot water.
They are often black and have a large surface area to absorb as much infrared energy as possible.