EXAMINATIONS FOR THE AWARD
OF THE HIGHER EDUCATION
CERTIFICATE (HEC)
FINAL EXAMINATION FOR SEMESTER 2
FACULTY
DEPARTMENT
ACADEMIC YEAR
SEMESTER
PAPER CODE
PAPER NAME
DATE
TIME
INSTRUCTIONS
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SCIENCE
PHYSICS
2023/2024
1
HEC 1215
WAVES, OPTICS and MODERN PHYSICS
12 / 05 / 2023
09H00 - 12H00
—————————————–
Non-programmable electronic calculators are permissible.
Any constants without numerical values must be used as is.
The format a.bc × 10n must be used for all numerical results.
DO NO OPEN this question paper until instructed to do so.
Answer only 4(Four) questions.
c
○2023
Physics Department, Kabale University
1. (a) Define the term reflection of light
(b) State the laws of reflection of light
[01]
[02]
(c) In a church choir loft, two parallel walls are 5.30 m apart. The singers
stand against the north wall. The organist faces the south wall, sitting
0.800 m away from it. To enable her to see the choir, a flat mirror 0.600
m wide is mounted on the south wall, straight in front of her. What
width of the north wall can the organist see? Suggestion: Draw a
top-view diagram to justify your answer.
[07]
(d) A periscope (Fig. 1) is useful for viewing objects that cannot be seen
directly. It can be used in submarines and when watching golf matches
or parades from behind a crowd of people. Suppose the object is a distance p1 from the upper mirror and the two flat mirrors are separated
by a distance h.
(i) Find the position of the image
[05]
(ii) What is the distance of the final image from the lower mirror?
[01]
(iii) Is the final image real or virtual?
[01]
(iv) Is it upright or inverted?
[01]
(v) What is its magnification?
[01]
(vi) Does it appear to be left–right reversed?
[01]
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○2023
Physics Department, Kabale University
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2. (a) With clear examples distinguish between transverse and longitudinal
waves
[04]
(b) Define the following terms
(i) amplitude
[01]
(ii) frequency
[01]
(c) A transverse wave on a string is described by the wave function
π
x + 4πt
y(x, t) = (0.120m) sin
8
(i) Determine the transverse speed and acceleration of the string at
t = 0.200 s for the point on the string located at x = 1.60 m. [08]
(ii) What are the wavelength, period, and speed of propagation of this
wave?
[06]
✠✠✠✠✠✠✠✠
3. (a) What is meant by a line spectrum?
[(02)]
(b) Explain how line spectrum accounts for existence of discrete energy
levels in an atom.
[(04)]
(c) The energy levels in mercury atom are -10.4 eV, -5.5 eV, -3.7 eV and
-1.6 eV.
(i) Find the ionization energy of mercury in joules
[(02)]
(ii) What is likely to happen if mercury atom in unexcited state is
bombarded with an electron of energy 4.0 eV, 6.7 eV or 11.0 eV?
[(04)]
(d) An X-ray tube is operated at 20k V with electron current 16m A in
the tube. Estimate the:
(i) number of electrons hitting the target per second.
[(02)]
(ii) rate of production of heat, assuming 99.5% of the kinetic energy
of electron is converted to heat. (e = 1.6 x 10-19 C)
[(04)]
(e) Give two uses of X-rays
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○2023
Physics Department, Kabale University
[(02)]
✠✠✠✠✠✠✠✠
4. (a) (i) Define the term binding energy
[(01)]
(ii) Sketch a graph showing the variation of binding energy per nucleon
with mass number
[(02)]
(iii) Use the sketch in (a)(i) to explain how energy is released in each
of the process of fusion and fission.
[(02)]
(b) Explain why a high temperature is required during fusion of nuclides.
[(02)]
(c) The isotope 238
92 U emits an alpha particle and forms an isotope of tho144
rium (Th), while the 235
92 U when bombarded by a neutron, forms 56 Ba,
9036 Kr and neutrons.
235
(i) Write the nuclear equation for the reaction of 238
92 U and 92 U. [(02)]
(ii) How does the reaction of
238
92 U
differ from that of
235
92 U
[(03)]
(d) A steel piston ring contains 15g of radioactive iron, 54
26 Fe. The activ5
ity of 54
26 Fe is 3.7 × 10 disintegration per second. After 100 days of
continuous use, the crankcase oil was found to have a total activity of
1.23 × 103 disintegrations per second. Find the
(i) Half-life of
54
26 Fe
[(04)]
(ii) Average mass of iron worn off the ring per day, assuming that all
the metal from the ring accumulates in the oil.
[(04)]
✠✠✠✠✠✠✠✠
5. (a) Describe briefly the mechanism of
(i) thermionic emission
[(03)]
(ii) photoelectric emission
[(03)]
(b) (i) Describe with the aid of a well labelled diagram, the structure and
mode of operation of a C.R.O
[(10)]
(ii) State the advantages of C.R.O over a moving coil voltmeter. [(02)]
✠✠✠✠✠✠✠✠
c
○2023
Physics Department, Kabale University
6. (a) State the laws of refraction
[02]
(b) A beam of light strikes the surface of water at an incidence angle of
600 . Determine the directions of the reflected and refracted rays [For
water take n = 1.33].
[06]
(c) (i) Define the terms critical and total internal reflection
[02]
(ii) Figure 2 shows an isosceles prism ABC of refractive index 1.51,
dipped in a liquid with its refracting edge downwards. A ray of
light incident on the prism at angle i = 34.60 emerges perpendicularly through the base.
Figure 1:
Calculate the refractive index of the liquid
[05]
(d) Light enters a solid pipe made of plastic having an index of refraction
of 1.60. The light travels parallel to the upper part of the pipe (Fig.
3). You want to cut the face AB so that all the light will reflect back
Figure 2:
into the pipe after it first strikes that face. What is the largest angle
θ can be if the pipe is in air?
[05]
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○2023
Physics Department, Kabale University
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7. (a) (i) Define optical path
[(01)]
(ii) Distinguish between constructive and destructive interference [(04)]
(b) With reference to Young’s double slit experiment
(i) Explain how an interference pattern is formed.
[(02)]
(ii) State what happen to the fringes when the source is moved nearer
to the slits.
[(02)]
(iii) State what happens to the fringes when the separation of the slits
is charged.
[(02)]
(iv) Describe the appearance of the fringes when white light is used.
[(03)]
(c) Calculate the separation of the slits if the distance from the slits to
the screen is 800mm and the 8th bright fringe is formed 5mm away
from the centre of the fringe system, given that wave length of light
is.
[(03)]
(d) With the aid of a diagram, describe how interference can be produced
by division of wave front.
[(03)]
✠✠✠✠END✠✠✠✠
c
○2023
Physics Department, Kabale University