Energy - Transfer by Heating
Metals are good conductors of heat because they have free electrons.

Energy - Transfer by Heating

This Physics quiz is called 'Energy - Transfer by Heating' and it has been written by teachers to help you if you are studying the subject at senior high school. Playing educational quizzes is one of the most efficienct ways to learn if you are in the 11th or 12th grade - aged 16 to 18.

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Energy can be transferred by many different methods and into many different forms. A lot of energy transfers involve heat which sometimes is useful and sometimes is wasted. In senior high school, you need to be able to recognize situations in which other forms of energy are transferred into heat energy, to identify if the heat energy is useful or wasted, how to reduce the heat energy losses from buildings and to be able to explain how heat energy moves from one place to another.

Energy transfers can be represented in different ways. One of these is by an energy transfer diagram. This has three parts and usually only shows the main useful energy transfer. The first part of the diagram indicates the energy input, for example, chemical energy in the fuel for a car engine.

The second part of the diagram shows the process (in our example, this would be a picture of a car engine). The third part indicates the useful energy output from the engine which is the kinetic energy.

A different way of representing energy transfers is a Sankey diagram. This is most commonly used to represent energy efficiency as it is drawn to scale and shows the useful energy transfers and the waste energies. A Sankey diagram is sometimes presented on squared paper, with each square representing a specific quantity of energy; other times, it is just drawn as two or more arrows, with the energy values written on the arrows. You may be asked to work out the efficiency of an energy transfer from the figures on a Sankey diagram so make sure that you revise how to do that.

Where you come across questions about reducing heat losses from buildings, you are expected to know what U-values are and what they tell you plus how and why the various methods of insulation work. For example, loft and cavity wall insulation works by trapping air, since air is a poor conductor of heat, it slows down the speed at which heat leaves a building. Higher tier candidates would be expected to relate heat insulation to the kinetic theory. An example of this would be to show that you understand why warmer air rises and how conduction of heat occurs in solids.

1.
Which surface is the best reflector of heat?
Red surface
Black surface
Blue surface
Shiny white surface
Any surface that reflects light efficiently will also reflect infrared radiation effectively too. Remember, heat radiation is made from infrared radiation, a member of the electromagnetic spectrum just beyond the red end of the visible light spectrum
2.
Which of the following is one reason why metals are good conductors of heat?
They are shiny
They have free electrons
They have a high resistance
They are rigid
Metals are good conductors because the free electrons within them are able to move throughout the material, helping to transfer the heat quickly
3.
What does the transfer of energy by conduction, convection and evaporation involve?
Radio waves
Particles
Sound waves
UV waves
All these processes need particles to occur. In conduction, the particles vibrate next to each other and pass heat on through the vibrations. In convection, the hotter particles vibrate more vigorously so they move further apart. This means the density of the hotter gas or liquid is lower so it rises through the colder parts which are more dense
4.
How does heat transfer through the vacuum of space?
By radiation
By conduction
By spacecraft
It doesn't
Space is a vacuum and as such there are no particles in it. This means that the only way for energy to travel through space is in the form of radiation as electromagnetic waves
5.
What does the rate at which an object transfers energy by heating depend on?
Surface area and volume
The material from which the object is made
The nature of the surface with which the object is in contact
All of the above
Many factors affect the speed of transfer of thermal energy, not just the temperature gradient
6.
Which of the following surfaces is the best absorber of heat?
Shiny surface
Black surface
White surface
Red surface
The best surface for absorbing heat is matt black, matt surfaces are better absorbers than shiny polished ones
7.
What factor will cause an object to lose its heat energy the fastest?
Heating the object
A smaller temperature difference between the object and its surroundings
A larger temperature difference between the object and its surroundings
Encasing the object in a blanket
A larger temperature difference means that the heat will be lost at a much faster pace as there is more energy to radiate to the environment. We call the temperature difference a temperature gradient. The bigger the gradient, the faster the heat flows and vice-versa. You will have noticed exactly this effect when plotting cooling curves on graph paper
8.
What is evaporation?
The process during which fastest moving particles of a liquid escape from the liquid's surface
The vaporization of the entire mass of the liquid as heat energy is applied
It is the collective movement of molecules in liquids and gasses
High energy particles knock lower energy particles out of the liquid and into the air
During evaporation, because the highest energy particles escape, the liquid left behind has a lower temperature. You may have seen this demonstrated using a hygrometer
9.
Which sentence best describes how conduction works?
Conduction involves vibrating particles passing the heat energy along
The heat is radiated into the surroundings
Warm particles rise and cold particles fall
Particles do not make contact with each other but are heated individually via an external source
This is the other reason why metals are good heat conductors - their particles are very closely packed so the vibrations are easily passed from one atom to the next
10.
What kind of surfaces is heat radiation emitted from?
Shiny surfaces
Dark surfaces
All surfaces
Kitchen surfaces
Any object with a temperature above absolute zero will emit heat radiation (infrared radiation). Hotter objects emit more than cooler ones
Author:  Martin Moore

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