The unit of energy density of a fuel is 

• J m^–2. 
• J m^–3. 
• J kg^–1. 
• kg J^–1. 

Which of the following is the best estimate for the overall efficiency of a typical coal power station? 

• 5%
• 30%
• 60%
• 90%

The power per unit length P of an oscillating water column (OWC) is due to the action of a surface wave of amplitude A.
Which of the following correctly relates P and A, and correctly identifies the nature of the energy of the water column? 

• A
• B
• C
• D

The average temperature of the surface of the Sun is about 20 times more than the average surface temperature of the Earth. The average power per unit area radiated by the Earth is P. The average power per unit area radiated by the Sun is 

• 20P. 
• 400P. 
• 8000 P. 
• 160 000 P. 

Global warming reduces the ice and snow cover on Earth. Which of the following correctly describes the changes in albedo and rate of energy absorption by Earth? 

• A
• B
• C
• D

The efficiency of a modern natural gas power station is approximately 

• 10%
• 50%
• 75%
• 90%

The rate of global warming might be reduced by 

• replacing the use of coal and oil with natural gas. 
• a reduction in the Earth’s albedo. 
• a reduction in carbon fixation. 
• an increase in deforestation. 

Greenhouse gases 

• reflect infrared radiation but absorb ultraviolet radiation. 
• reflect ultraviolet radiation but absorb infrared radiation. 
• transmit infrared radiation but absorb ultraviolet radiation. 
• transmit ultraviolet radiation but absorb infrared radiation. 

The Sankey diagram shows a typical fossil-fuel plant of total efficiency 40 %. There are frictional, electrical transmission and energy losses to the lower temperature surroundings. Which branch represents the electrical energy arriving at the customer? 

• A
• B
• C
• D

The absolute temperature of a black body increases by 2 %. What is the percentage increase in the power emitted by the black body?

• 2

• 4

• 8

• 16