Two pulses are travelling towards each other.

What is a possible pulse shape when the pulses overlap?

A

Which of the following is not a primary energy source? 

A. Wind turbine 

B. Jet Engine 

C. Coal-fired power station 

D. Nuclear power station

B

What are the principal energy changes in a photovoltaic cell and in a solar heating panel? 

A

The average surface temperature of Mars is approximately 200 K and the average surface temperature of Earth is approximately 300 K. Mars has a radius half that of Earth. Assume that both Mars and Earth act as black bodies.

What is $\frac{\text{power radiated by Mars}}{\text{power radiated by Earth}}$?

A.  20
B.  5
C.  0.2
D.  0.05

D

Planet X and planet Y both emit radiation as black bodies. Planet X has a surface temperature that is less than the surface temperature of planet Y.

What is the graph of the variation of intensity I with wavelength λ for the radiation emitted by planet Y? The graph for planet X is shown dotted.

D

The orbital radius of the Earth around the Sun is 1.5 times that of Venus. What is the intensity of solar radiation at the orbital radius of Venus?

A. 0.6 kW m^-2

B. 0.9 kW m^-2

C. 2 kW m^-2

D. 3 kW m^-2

D

This had a low discrimination index at both SL and HL and although the correct answer was the most popular, all options gained high support. Candidates should be reminded that they have a data booklet and become familiar with its contents before the exam.

What are the units of specific energy and energy density?

B

What are the principal roles of a moderator and of a control rod in a thermal nuclear reactor?

C

The energy density of a substance can be calculated by multiplying its specific energy with which quantity?

A. mass

B. volume

C. $\frac{\text{mass}}{\text{volume}}$

D. $\frac{\text{volume}}{\text{mass}}$

C

The three statements give possible reasons why an average value should be used for the solar constant.

I.   The Sun’s output varies during its 11 year cycle.
II.  The Earth is in elliptical orbit around the Sun.
III. The plane of the Earth’s spin on its axis is tilted to the plane of its orbit about the Sun.

Which are the correct reasons for using an average value for the solar constant?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

A

What is the main role of carbon dioxide in the greenhouse effect?

A. It absorbs incoming radiation from the Sun.

B. It absorbs outgoing radiation from the Earth.

C. It reflects incoming radiation from the Sun.

D. It reflects outgoing radiation from the Earth.

B

A wind turbine has a power output p when the wind speed is v. The efficiency of the wind turbine does not change. What is the wind speed at which the power output is $\frac{p}{2}$?

A.     $\frac{v}{4}$

B.     $\frac{v}{\sqrt{8}}$

C.     $\frac{v}{2}$

D.     $\frac{v}{\sqrt[3]{2}}$

D

A black body at temperature T emits radiation with peak wavelength ${\lambda }_{\text{ρ}}$ and power P. What is the temperature of the black body and the power emitted for a peak wavelength of $\frac{{\lambda }_{\text{ρ}}}{2}$?

D

What is equivalent to $\frac{\text{specific energy of a fuel}}{\text{energy density of a fuel}}$?

A.     density of the fuel

B.     $\frac{1}{\text{density of the fuel}}$

C.     $\frac{\text{energy stored in the fuel}}{\text{density of the fuel}}$

D.     $\frac{\text{density of the fuel}}{\text{energy stored in the fuel}}$

B

Mars and Earth act as black bodies. The $\frac{\text{power radiated by Mars}}{\text{power radiated by the Earth}}=p$ and $\frac{\text{absolute mean temperature of the surface of Mars}}{\text{absolute mean temperature of the surface of the Earth}}=t$.

What is the value of $\frac{\text{radius of Mars}}{\text{radius of the Earth}}$?

A.     $\frac{p}{t^4}$

B.     $\frac{\sqrt{p}}{t^2}$

C.     $\frac{t^4}{p}$

D.     $\frac{t^2}{\sqrt{p}}$

B

Which is correct for a black-body radiator?

A.  The power it emits from a unit surface area depends on the temperature only.

B.  It has an albedo of 1.

C.  It emits monochromatic radiation whose wavelength depends on the temperature only.

D.  It emits radiation of equal intensity at all wavelengths.

A

Three gases in the atmosphere are

          I.     carbon dioxide (CO₂)

          II.     dinitrogen monoxide (N₂O)

          III.     oxygen (O₂).

Which of these are considered to be greenhouse gases?

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A

A fuel has mass density $\rho$ and energy density $u$. What mass of the fuel has to be burned to release thermal energy $E$?

A.  $\frac{\rho E}{u}$

B.  $\frac{uE}{\rho }$

C.  $\frac{\rho u}{E}$

D.  $\rho uE$

A

A nuclear power station contains an alternating current generator. What energy transfer is performed by the generator?

A.  Electrical to kinetic

B.  Kinetic to electrical

C.  Nuclear to kinetic

D.  Nuclear to electrical

B

The Sankey diagram represents the energy flow for a coal-fired power station.

What is the overall efficiency of the power station? 

A. 0.3 

B. 0.4 

C. 0.6 

D. 0.7

A

The main role of a moderator in a nuclear fission reactor is to

A.  slow down neutrons.

B.  absorb neutrons.

C.  reflect neutrons back to the reactor.

D.  accelerate neutrons.

A

A room is at a constant temperature of 300 K. A hotplate in the room is at a temperature of 400 K and loses energy by radiation at a rate of P. What is the rate of loss of energy from the hotplate when its temperature is 500 K?

A.  $\frac{4^4}{5^4}$P

B.  $\frac{5^4+3^4}{4^4+3^4}$P

C.  $\frac{5^4}{4^4}$P

D.  $\frac{5^4-3^4}{4^4-3^4}$P

D

What is the function of control rods in a nuclear power plant?

A.   To slow neutrons down

B.   To regulate fuel supply

C.   To exchange thermal energy

D.   To regulate the reaction rate

D

Light of intensity I₀ is incident on a snow-covered area of Earth. In a model of this situation, the albedo of the cloud is 0.30 and the albedo for the snow surface is 0.80. What is the intensity of the light at P due to the incident ray I₀?

A.   0.14 I₀

B.   0.24 I₀

C.   0.50 I₀

D.   0.55 I₀

B

Wind of speed $v$ flows through a wind generator. The wind speed drops to $\frac{v}{3}$ after passing through the blades. What is the maximum possible efficiency of the generator?

A.  $\frac{1}{27}$

B.  $\frac{8}{27}$

C.  $\frac{19}{27}$

D.  $\frac{26}{27}$

D

Both HL and SL candidates found this question more challenging, with the large majority of candidates split between the three incorrect options. Option A was the most frequent (incorrect) answer, suggesting that candidates had correctly determined the proportion lost rather than that remaining to produce energy. Candidates should be reminded to consider whether or not their quantitative solutions are realistic; it is highly unlikely that a generator would have maximum efficiency of 1/27 (option A).

A photovoltaic panel of area S has an efficiency of 20 %. A second photovoltaic panel has an efficiency of 15 %. What is the area of the second panel so that both panels produce the same power under the same conditions?

A.   $\frac{S}{3}$

B.   $\frac{3S}{4}$

C.   $\frac{5S}{4}$

D.   $\frac{4S}{3}$

D

The diagram shows, for a region on the Earth’s surface, the incident, radiated and reflected intensities of the solar radiation.

What is the albedo of the region?

A.  $\frac{1}{4}$

B.  $\frac{1}{3}$

C.  $\frac{3}{4}$

D.  $1$

A

This question was well answered by both HL and SL candidates.

A neutron collides head-on with a stationary atom in the moderator of a nuclear power station. The kinetic energy of the neutron changes as a result. There is also a change in the probability that this neutron can cause nuclear fission.

What are these changes?

B

The average temperature of the surface of a planet is five times greater than the average temperature of the surface of its moon. The emissivities of the planet and the moon are the same. The average intensity radiated by the planet is $I$. What is the average intensity radiated by its moon?

A.  $\frac{I}{25}$

B.  $\frac{I}{125}$

C.  $\frac{I}{625}$

D.  $\frac{I}{3125}$

C

A beaker containing 1 kg of water at room temperature is heated on a 400 W hot plate. The specific heat capacity of water is 4200 J kg^–1 K^–1.

The temperature of the water increases until it reaches a constant value. It is then removed from the hot plate.

What will be the initial rate of change of temperature?

A. 10 K s^–1

B. 1 K s^–1

C. 0.1 K s^–1

D. 0.01 K s^–1

C

Which change produces the largest percentage increase in the maximum theoretical power output of a wind turbine?

A. Doubling the area of the blades

B. Doubling the density of the fluid

C. Doubling the radius of the blades

D. Doubling the speed of the fluid

D

The diagram shows a simple climate model for the Earth.

What does this model predict for the average albedo of the Earth?

A.     0.30

B.     0.51

C.     0.70

D.     0.81

A

A black body emits radiation with its greatest intensity at a wavelength of I_max. The surface temperature of the black body doubles without any other change occurring. What is the wavelength at which the greatest intensity of radiation is emitted?

A. I_max

B. $\frac{\text{I}{}_{\text{max}}}{\text{2}}$

C. $\frac{\text{I}{}_{\text{max}}}{\text{4}}$

D. $\frac{\text{I}{}_{\text{max}}}{\text{16}}$

B

A black-body radiator emits a peak wavelength of ${\lambda }_{\text{max}}$ and a maximum power of $P_0$. The peak wavelength emitted by a second black-body radiator with the same surface area is $2 {\lambda }_{\text{max}}$. What is the total power of the second black-body radiator?

A.  $\frac{1}{16}{P}_0$

B.  $\frac{1}{2}{P}_0$

C.  $2P_0$

D.  $16P_0$

A

The Sankey diagram shows the energy transfers in a nuclear power station.

Electrical power output of the power station is 1000 MW.

What is the thermal power loss in the heat exchanger?

A.  500 MW

B.  1000 MW

C.  1500 MW

D.  2500 MW

B

Three methods for the production of electrical energy are

I. wind turbine

II. photovoltaic cell

III. fossil fuel power station.

Which methods involve the use of a primary energy source?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

D

This question seems to have prompted some discussion among teachers and slightly more candidates chose response A than the others. Primary energy is defined as coming from a natural resource so whereas fossil fuels are non-renewable they are a primary energy resource. Also, a photovoltaic cell produces electricity, defined as a secondary energy source from a primary energy source, the sun. The clue is given in the question ‘involve the USE of a primary energy source’.

Photovoltaic cells and solar heating panels are used to transfer the electromagnetic energy of the Sun’s rays into other forms of energy. What is the form of energy into which solar energy is transferred in photovoltaic cells and solar heating panels?

A

The Sankey diagrams for a filament lamp and for an LED bulb are shown below.

What is the efficiency of the filament lamp and the LED bulb?

A

Most power stations rely on a turbine and a generator to produce electrical energy. Which power station works on a different principle?

A. Nuclear

B. Solar

C. Fossil fuel

D. Wind

B

Three energy sources for power stations are

       I.     fossil fuel

       II.     pumped water storage

       III.     nuclear fuel.

Which energy sources are primary sources?

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III 

B

Which of the energy sources are classified as renewable and non-renewable?

C

Three mechanisms that affect the composition of the atmosphere of the Earth are:

I.   Loss of forests that would otherwise store carbon dioxide – CO₂
II.  Release of methane – CH₄ by the digestive system of grazing animals
III. Increase of nitrous oxide – N₂O due to extensive use of fertilizer

Which of these statements describe a process that contributes to global warming?

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

D

This question was well answered by candidates, although option A was a frequent distractor suggesting candidates may be less clear about the role of nitrous oxide in global warming.

In a simple climate model for a planet, the incoming intensity is 400 W m⁻² and the radiated intensity is 300 W m⁻².

The temperature of the planet is constant. What are the reflected intensity from the planet and the albedo of the planet?

A

What is the function of the moderator in a thermal nuclear fission reactor?

A. To decrease the kinetic energy of neutrons emitted from fission reactions

B. To increase the kinetic energy of neutrons emitted from fission reactions

C. To decrease the overall number of neutrons available for fission

D. To increase the overall number of neutrons available for fission

A

The following are energy sources.

I.    a battery of rechargeable electric cells
II.   crude oil
III.  a pumped storage hydroelectric system

Which of these are secondary energy sources?

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

B

What is meant by the statement that the average albedo of the Moon is 0.1?

A. 10% of the radiation incident on the Moon is absorbed by its surface

B. 10% of the radiation emitted by the Moon is absorbed by its atmosphere

C. 10% of the radiation incident on the Moon is reflected by its surface

D. 10% of the radiation emitted by the Moon is at infrared wavelengths

C