PMPH130 Waves Tutorial Sheet

SCHOOL OF MEDICINE AND HEALTH SCIENCES
DEPARTMENT OF BASIC SCIENCES
PMPH 130- A’ LEVEL PHYSICS

TUTORIAL SHEET
TOPIC: WAVES
LECTURER: MR MUBITA.D
2022 -2023 ACADEMIC YEAR
Page 1 of 6
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1) a). In a double-slit experiment using light from a helium–neon laser, a student obtained the
following results: width of 10 fringes 10x = 1.5 cm separation of slits a = 1.0 mm slit-to-screen
distance D = 2.40 m. Determine the wavelength of the light. [2]
b). A hydrogen discharge lamp produces a spectral line of wavelength 656 nm. Calculate the
angles at which a diffraction grating, with 5000 lines cm−1, would produce the first and second
maxima for this light. [2]
c). Explain what is meant by the term superposition. [2]
d). In a Young double-slit experiment using yellow light of wavelength 590 nm from a sodium
discharge tube, a student sets up a screen 1.8 m from the double slit. He measures the distance
between 12 fringes as 16.8 mm. Calculate the separation of the slits. [3]
e). State the effect of:
i. using slits of narrower width (but the same separation) [3]
ii. using slits with a smaller separation but of the same width [3]
[TOTAL: 15 MARKS]
2. a). A laser light is described as producing light which is both highly coherent and highly
monochromatic. Explain what is meant by the terms coherent and monochromatic. [1]
b). Figure 14.30 shows the setup used to analyse the spectrum of a sodium discharge lamp
using a diffraction grating with 5000 lines cm−1. Figure 14.31 shows the spectral lines observed in
the developed photographic film.
Fig. 14.30
Figure 14.31 Spectral lines produced

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i. Explain why two spectra are observed. [2]
ii. Study the two spectra and describe two differences between them. [2]
iii. The green maximum near end A is at an angle θ of 19.5°. Calculate the wavelength of the
green light. [3]
iv. Calculate the angle produced by the second green line. [2]
[TOTAL: 10 MARKS]
3. a). Monochromatic light is incident normally on a diffraction grating having 3000 lines per
centimetre. The angular separation of the zeroth- and first-order maxima is found to be 10°.
Calculate the wavelength of the incident light. [3]
b). White light is incident normally on a diffraction grating with a slit separation d of
2.00 ×10−6 m.
i. Calculate the angle between the red and violet ends of the first-order spectrum. [2]
ii. The visible spectrum has wavelengths between 400 nm and 700 nm. Explain why the second-
and third-order spectra overlap. [3]
[TOTAL: 8 MARKS]
4. a). Explain what is meant by the term destructive interference. [2]

b). A student sets up an experiment to investigate the interference pattern formed by microwaves
of wavelength 1.5 cm. The apparatus is set up as in Figure 14.17.
Fig. 14.17
The distance between the centres of the two slits is 12.5 cm. The detector is centrally placed 1.2 m
from the metal plates where it detects a maximum. The student moves the detector 450 cm across
the bench parallel to the plates.
i. Calculate how many maxima the detector will be moved through. [3]
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ii. Calculate the frequency of these microwaves. [2]
iii. Explain what is meant by the diffraction of a wave. [2]
c). Figure 14.32 shows waves, in a ripple tank, spreading out from two slits.
Fig. 14.32
On a copy of Figure 14.32, draw:
i. a line showing points along the central maximum – label this line 0 [1]
ii. a line showing the points along first maximum – label this line 1 [1]
iii. a line showing points along one of the first minima – label this line min. [1]
d). The centres of the slits are 12 cm apart. At a distance of 60 cm from the barrier, the first maxima
are 18 cm either side of the central maximum. Calculate the wavelength of the waves. You may
assume that the formula developed for light waves is applicable in this example. [3]
[TOTAL: 15 MARKS]
5. a). A stationary (standing) wave is set up on a vibrating spring. Adjacent nodes are separated
by 25 cm. Determine:
i. the wavelength of the stationary wave [2]
ii. the distance from a node to an adjacent antinode [2]
b). For sound waves of frequency 2500 Hz, it is found that two nodes are separated by 20 cm,
with three antinodes between them.
i. Determine the wavelength of these sound waves. [2]
ii. Use the wave equation v = f λ to determine the speed of sound in air. [2]
c). In a resonance tube experiment, resonance is obtained for sound waves of frequency 630 Hz
when the length of the air column is 12.6 cm and again when it is 38.8 cm. Determine:
i. the wavelength of the sound waves causing resonance [2]
ii. the end-correction for this tube [2]
iii. the speed of sound in air [2]
d). Define fundamental frequency [1]
[TOTAL: 15 MARKS]
Page 5 of 6
6. A tuning fork which produces a note of 256 Hz is placed above a tube which is nearly filled with
water. The water level is lowered until resonance is first heard.
a) Explain what is meant by the term resonance. [1]
b) The length of the column of air above the water when resonance is first heard is 31.2 cm.
Calculate the speed of the sound wave. [2]
c) What is the difference between phase and path difference [2]
[TOTAL: 5 MARKS]
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SCHOOL OF MEDICINE AND HEALTH SCIENCES

DEPARTMENT OF BASIC SCIENCES

PMPH 130- A’ LEVEL PHYSICS

2022 -2023 ACADEMIC YEAR

Figure 14.31 Spectral lines produced

4. a). Explain what is meant by the term destructive interference. [2]

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