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%
25%
99%
75%
98%
0%
97%
0%
96%
Q.2.
A roof receives 1,000 W/m 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%?
100%
1.4 W
0%
1.6 W
0%
14,000 W
0%
14 kW
Q.3.
If a filament light bulb consumes 150 J/s and produces 12 J/s of light energy, what is its efficiency?
50%
0.08%
50%
8%
0%
12.5%
0%
1,250%
Q.4.
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?
33%
It remains the same
67%
It increases
0%
It decreases
0%
A Sankey diagram is needed to work it out
Q.5.
What is the efficiency of a computer that consumes 25 J/s of electrical energy and wastes 9 J/s of heat energy?
0%
278%
0%
36%
100%
0.36%
0%
64%
Q.6.
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 ?
50%
The fire is 100% efficient
0%
The fire is between 90% and 100% efficient
50%
The fire is between 85% and 90% efficient
0%
The efficiency of the fire is less than 85%
Q.7.
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?
33%
2.95 W
67%
3.95W
0%
4.95 W
0%
5.95 W
Q.8.
As a train travels along its rails, its wheels create sparks. Apart from this light energy, what other forms of energy are wasted?
0%
Sound only
0%
Heat only
50%
Kinetic only
50%
Heat and sound
Q.9.
How is the efficiency of an energy transfer expressed?
50%
As a percentage
0%
As a proportion
0%
As a ratio
50%
In kilowatt hours
Q.10.
What is a Sankey diagram?
0%
A diagram of the London Underground railroad system
50%
A diagram drawn to scale (usually using squared paper) to represent the efficiency of an energy transfer
50%
A circuit diagram for a machine that can be used for measuring the efficiency of energy transfers
0%
A graph showing only the percentage of useful energy produced in an energy transfer
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