Quiz about Heat Energy
In GCSE Science students will spend some time looking at the transfer of heat energy. This is the third of eight quizzes on the topic and it looks at efficiency in energy transfers and how some energy (in the form of heat, light or sound for example) is wasted.
When energy is transferred only part of it is usefully transferred - the rest is ‘lost’. Only it isn't really lost. It is still there but in different forms and spread out into the surroundings, so we refer to it as 'wasted energy'. This wasted energy is often in the form of heat but could be in other forms like light and sound. One way or another, the energy that has been transferred to the surroundings makes them warmer. The wasted energy is increasingly spread out and is therefore a lot less useful.
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In mechanical systems, an important cause of wasted energy is friction. Friction transfers kinetic energy into heat and sound which dissipates directly into the surroundings. As the sound energy passes through the air (or any other medium) it is transferred back into kinetic energy as it causes the particles to vibrate. The sound energy is thus absorbed and spread through the medium.
In electrical systems, as the free electrons move through a conductor they collide with its atoms. Some of the electrical energy is therefore transferred into kinetic energy by the particles of the conductor, making them vibrate more. Vibrating particles transfer kinetic energy into heat energy and the conductor becomes warmer. This sets up a temperature gradient which transfers the thermal energy into the surroundings, wasting some of the original electrical energy. Sparks in electrical systems also waste some energy in the form of light, which spreads out into the surroundings.
No attempt to transfer one form of energy into another form of useful energy is ever 100% successful. Some come pretty close but there is always a bit of energy that is wasted. In class, you will have come across Sankey diagrams. These are simply scale drawings on graph paper that show how much energy is transferred usefully and how much is wasted. The proportion of energy that is usefully transferred is called the efficiency. Efficiency can be worked out by dividing the amount of useful energy obtained by the amount of energy at the start of the transfer, then multiplying it by 100 to express it as a percentage.
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1.
|
As a train travels along its rails, its wheels create sparks. Apart from this light energy, what other forms of energy are wasted? |
|
[ ] |
Sound only |
[ ] |
Heat only |
[ ] |
Kinetic only |
[ ] |
Heat and sound |
|
|
2.
|
What is a Sankey diagram? |
|
[ ] |
A diagram of the London Underground railway system |
[ ] |
A diagram drawn to scale (usually using squared paper) to represent the efficiency of an energy transfer |
[ ] |
A circuit diagram for a machine that can be used for measuring the efficiency of energy transfers |
[ ] |
A graph showing only the percentage of useful energy produced in an energy transfer |
|
|
3.
|
How is the efficiency of an energy transfer expressed? |
|
[ ] |
As a percentage |
[ ] |
As a proportion |
[ ] |
As a ratio |
[ ] |
In kilowatt hours |
|
|
4.
|
If a filament light bulb consumes 150 J/s and produces 12 J/s of light energy, what is its efficiency? |
|
[ ] |
0.08% |
[ ] |
8% |
[ ] |
12.5% |
[ ] |
1,250% |
|
|
5.
|
A houseowner replaces their filament light bulbs with LED lighting. This is 85% efficient and requires only a 7 watt input. What is the useful power output of the new lights? |
|
[ ] |
2.95 W |
[ ] |
3.95W |
[ ] |
4.95 W |
[ ] |
5.95 W |
|
|
6.
|
When the outside temperature is cold, the air inside a car is warmed by some of the thermal energy from the engine. What effect does this have on the overall efficiency of the car engine? |
|
[ ] |
It remains the same |
[ ] |
It increases |
[ ] |
It decreases |
[ ] |
A Sankey diagram is needed to work it out |
|
|
7.
|
What is the efficiency of a computer that consumes 25 J/s of electrical energy and wastes 9 J/s of heat energy? |
|
[ ] |
278% |
[ ] |
36% |
[ ] |
0.36% |
[ ] |
64% |
|
|
8.
|
Burning 2kg of wood in a particular woodburning stove releases 29 MJ of heat energy. If 25 MJ of that heat is transferred to the room, which of the following statements is true? |
|
[ ] |
The fire is 100% efficient |
[ ] |
The fire is between 90% and 100% efficient |
[ ] |
The fire is between 85% and 90% efficient |
[ ] |
The efficiency of the fire is less than 85% |
|
|
9.
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Distributing electrical energy through the 400,000 V cables of the National Grid wastes some of the energy of the electricity (see below). What is the efficiency of this part of the system to the nearest whole number?
Total power generated: 62,161.5 MW
Step-up transformer losses: 157 MW
Step-down transformer losses: 142 MW
Losses caused by heating of the cables during transmission: 1.4% |
|
[ ] |
99% |
[ ] |
98% |
[ ] |
97% |
[ ] |
96% |
|
|
10.
|
A roof receives 1,000 W/m2 of energy from the Sun on a clear, sunny day. How many watts would be produced from a 5cm wide by 20cm long solar cell positioned on the roof if the efficiency of the solar cell is 14%? |
|
[ ] |
1.4 W |
[ ] |
1.6 W |
[ ] |
14,000 W |
[ ] |
14 kW |
|
|
1.
|
As a train travels along its rails, its wheels create sparks. Apart from this light energy, what other forms of energy are wasted? |
|
[ ] |
Sound only |
[ ] |
Heat only |
[ ] |
Kinetic only |
[x] |
Heat and sound |
|
|
2.
|
What is a Sankey diagram? |
|
[ ] |
A diagram of the London Underground railway system |
[x] |
A diagram drawn to scale (usually using squared paper) to represent the efficiency of an energy transfer |
[ ] |
A circuit diagram for a machine that can be used for measuring the efficiency of energy transfers |
[ ] |
A graph showing only the percentage of useful energy produced in an energy transfer |
|
|
3.
|
How is the efficiency of an energy transfer expressed? |
|
[x] |
As a percentage |
[ ] |
As a proportion |
[ ] |
As a ratio |
[ ] |
In kilowatt hours |
|
|
4.
|
If a filament light bulb consumes 150 J/s and produces 12 J/s of light energy, what is its efficiency? |
|
[ ] |
0.08% |
[x] |
8% |
[ ] |
12.5% |
[ ] |
1,250% |
|
|
5.
|
A houseowner replaces their filament light bulbs with LED lighting. This is 85% efficient and requires only a 7 watt input. What is the useful power output of the new lights? |
|
[ ] |
2.95 W |
[ ] |
3.95W |
[ ] |
4.95 W |
[x] |
5.95 W |
|
|
6.
|
When the outside temperature is cold, the air inside a car is warmed by some of the thermal energy from the engine. What effect does this have on the overall efficiency of the car engine? |
|
[ ] |
It remains the same |
[x] |
It increases |
[ ] |
It decreases |
[ ] |
A Sankey diagram is needed to work it out |
|
|
7.
|
What is the efficiency of a computer that consumes 25 J/s of electrical energy and wastes 9 J/s of heat energy? |
|
[ ] |
278% |
[ ] |
36% |
[ ] |
0.36% |
[x] |
64% |
|
|
8.
|
Burning 2kg of wood in a particular woodburning stove releases 29 MJ of heat energy. If 25 MJ of that heat is transferred to the room, which of the following statements is true? |
|
[ ] |
The fire is 100% efficient |
[ ] |
The fire is between 90% and 100% efficient |
[x] |
The fire is between 85% and 90% efficient |
[ ] |
The efficiency of the fire is less than 85% |
|
|
9.
|
Distributing electrical energy through the 400,000 V cables of the National Grid wastes some of the energy of the electricity (see below). What is the efficiency of this part of the system to the nearest whole number?
Total power generated: 62,161.5 MW
Step-up transformer losses: 157 MW
Step-down transformer losses: 142 MW
Losses caused by heating of the cables during transmission: 1.4% |
|
[ ] |
99% |
[x] |
98% |
[ ] |
97% |
[ ] |
96% |
|
|
10.
|
A roof receives 1,000 W/m2 of energy from the Sun on a clear, sunny day. How many watts would be produced from a 5cm wide by 20cm long solar cell positioned on the roof if the efficiency of the solar cell is 14%? |
|
[x] |
1.4 W |
[ ] |
1.6 W |
[ ] |
14,000 W |
[ ] |
14 kW |
|
|