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Date November 2011 Marks available 9 Reference code 11N.2.SL.TZ0.8
Level Standard level Paper Paper 2 Time zone Time zone 0
Command term Explain, Outline, Show that, and Suggest Question number 8 Adapted from N/A

Question

This question is in two parts. Part 1 is about the greenhouse effect. Part 2 is about an electric motor.

Part 1 Greenhouse effect

Describe what is meant by the greenhouse effect in the Earth’s atmosphere.

[3]
a.

The graph shows the variation with frequency of the percentage transmittance of electromagnetic waves through water vapour in the atmosphere.

(i) Show that the reduction in percentage transmittance labelled X occurs at a wavelength equal to approximately 5 μm.

(ii) Suggest, with reference to resonance, the possible reasons for the sharp reduction in percentage transmittance at a wavelength of 5 μm.

(iii) Explain how the reduction in percentage transmittance, labelled X on the graph opposite, accounts for the greenhouse effect.

(iv) Outline how an increase in the concentration of greenhouse gases in the atmosphere may lead to global warming.

[9]
b.

Markscheme

effect caused by gas such as H2O/NH3/CH4/CO2/greenhouse gas in the atmosphere;
gas absorbs outgoing (long wave) radiation from Earth;
gas re-radiates some of the energy back to Earth;

a.

(i) \(\frac{{3.0 \times {{10}^8}}}{{6.5 \times {{10}^{13}}}} = 4.6\left( {\mu m} \right)\);
≈5(μm)

(ii) water vapour molecules have a natural frequency of oscillation;
if this frequency of oscillation is \(6.5 \times {10^{13}}\) / reference to frequency at X;
due to resonance this radiation is readily absorbed by the molecules / the radiation matches the natural frequency of oscillation;

or

X is a natural frequency (of oscillation) of water molecule;
so resonance effects mean that molecules are excited at this frequency;
and energy is removed/less energy transmitted from electromagnetic waves at this (particular) frequency;

(iii) energy gained by absorption needs to be re-emitted (as molecules de-excite);
in other directions / some returns to Earth;

(iv) more greenhouse gases means that there is more absorption of outgoing radiation;
therefore more energy returns to Earth;
leading to a further/greater increase in the temperature of the surface (of Earth);

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Core » Topic 4: Waves » 4.2 – Travelling waves
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