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Date May 2015 Marks available 3 Reference code 15M.2.HL.TZ2.4
Level Higher level Paper Paper 2 Time zone Time zone 2
Command term Determine and Outline Question number 4 Adapted from N/A

Question

This question is about the properties of waves.

Microwaves from a microwave transmitter are reflected from two parallel sheets, A and B. Sheet A partially reflects microwave energy while allowing some to pass through. All of the microwave energy incident on sheet B is reflected.

Sheet A is fixed and sheet B is moved towards it. While sheet B is moving, the intensity of the signal detected at the receiver goes through a series of maximum and minimum values.

 

Outline why a minimum in the intensity occurs for certain positions of sheet B.

[3]
a.

The apparatus is arranged to demonstrate diffraction effects.

The microwaves emerge from the transmitter through an aperture that acts as a single slit.

(i) Outline what is meant by diffraction.

(ii) A maximum signal strength is observed at P. When the receiver is moved through an angle \(\theta \), a first minimum is observed. The width of the aperture of the transmitter is 60 mm. Estimate the value of \(\theta \).

[3]
c.

Microwaves can be used to demonstrate polarization effects. Outline why an ultrasound receiver and transmitter cannot be used to demonstrate polarization.

[2]
d.

Markscheme

mention of interference;
interference is between reflected waves from both reflectors;
minimum caused (by destructive interference) when crest meets trough/when path difference is \(\frac{\lambda }{2}\)
/ (completely) out of phase / phase difference of \(\pi \)/180º / OWTTE;
minimum occurs when twice the distance between plates is
\(\left( {n + \frac{1}{2}} \right)\lambda \);

Ignore references to standing waves.

a.

(i) spreading out of a wave; (do not allow “bending” even if context is obstacle)
when it meets an aperture/gap/slit/obstacle;
Allow credit for answers appearing on clear labelled diagram for both marks.

(ii) \(\left( {\theta  = \frac{{32}}{{60}} = } \right)0.533\left( {{\rm{rad}}} \right)\) or 30.6(º);
Award [0] for calculation that uses 1.22 (0.65 rad).
Award
[0] for 0.533º or 30.6 rad.
At least one centre is using the abbreviation
c
for rad. Please allow this.

c.

sound waves (in air) are longitudinal;
longitudinal waves cannot be polarized / only transverse waves can be polarized;

Award [0] for any suggestion that ultrasound is an electromagnetic wave.

d.

Examiners report

[N/A]
a.
[N/A]
c.
[N/A]
d.

Syllabus sections

Core » Topic 4: Waves » 4.3 – Wave characteristics
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