SMJK Yu Hua, Kajang, Selangor

STPM Trial Examination

Physics Paper 3
October 2019

Form : 6AS1 Prepared by : Pn Rosmaya Mokhtar

Date :3rd October 2019 (Thursday) Verified by ; Pn. Dayang Setiah

Time : 11:35 am – 1:05 pm

Number of printed pages : 5
Section A. (15 marks)
Answer all questions in this section.

1. An object of mass m undergoes a simple harmonic motion with frequency f and amplitude A. The maximum
restoring force is

2. The figure below shows two simple pendulums X and Y having the same lengths and same both sizes and a
simple pendulum Z whose length can be varied.

The pendulum X and pendulum Y will oscillate after the pendulum Z is set into oscillations in a plane parallel
to the wall. Which of the following graphs below shows the variation of the amplitude a for the pendulum X
and pendulum Y with frequency f of the pendulum Z when the length of the pendulum Z is varied?

3. A particle executes simple harmonic motion of amplitude A, at what distance from mean position its
kinetic energy is equal to its potential energy?
A. 0.51 A B. 0.61 A C. 0.71 A D. 0.81 A

4. The figure below shows the vibrations for the fundamental frequency, frequency of the first overtone
and frequency of the second overtone for a sound instrument.

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 These vibrations can also be produced by
A. Striking a tuning fork. B. Blowing across the open end of a pen cover.
C. Connecting a low alternating voltage to a loudspeaker D. Plucking a stretched string

5. Three successive overtones emitted by a pipe are at frequencies 210 Hz, 350 Hz and 490Hz. What is the
fundamental frequency?
A. 35 Hz B. 70 Hz C. 140 Hz D. 210 Hz

6. The displacement of a bob of a simple pendulum at time t is given by

where x is in metres and t in seconds. What is the magnitude of the maximum velocity of the bob?
A. 0.08 m s-1 B. 2.6 m s-1 C. 82 m s-1 D. 400 m s-1

7. A ray of light in a medium is incident towards the boundary of the first and second medium. Total internal
reflection occurs when the angle of incidence exceeds a certain value. Which of the following statements is
true concerning the incident ray ?
A The light is monochromatic
B. The light must be of sufficient intensity
C. The velocity of light in the first medium is less than the velocity of light in the second medium
D. The light’s frequency in the first medium is higher than the light’s frequency in the second medium

8. A concave lens of local length 10 cm is placed next to another concave lens of focal length 20 cm. If a point
object is placed at the primary focus of the first lens, where would be the emerging ray emerge from the first
lens if the distance between the two lenses is 25 cm ?
A. 5 cm from the first lens B. 5 cm from the second lens
C. 10 cm from the first lens D. 10 cm from the second lens

9. In a Young’s two-slit experiment, the two slits are illuminated with white light. Which of the following
observations is most probable ?
A. No fringes can be observed
B. The central fringe is black with black and white fringe on either side
C. The central fringe is white with coloured fringes on either side
D. The central fringe is black with coloured fringes on either side

10. A diffraction grating is ruled with 750 lines per milimetre when monochromatic light falls normally on the
grating. The second-order diffracted beams each making an angle of 180 with the normal to the grating are
observed on the far side of the grating. Find the frequency of the light
A. 1.9 x 1014 Hz B. 3.6 x 1014 Hz C. 1.5 x 1015 Hz D. 4.8 x 1015Hz

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11. A quantum of monochromatic light with energy 3.5 x 10-19 J falls on the cathode of a photocell. The current
flows through the cell is reduced to zero by supplying a stopping potential of 0.25 V. What is the work
function of the cathode?
A. 2.5 x 10-19 J B. 2.9 x 10-19 J C. 3.1 x 10-19 J D. 3.5 x 10-19 J

12. The figure below shows two energy levels of an atom. What is the wavelength of the photon emitted when
change of energy occurs between the two energy levels ?

13. The characteristic lines of an X-ray spectrum are cause by

A. collision of energetic incident electron with target atom
B. deceleration experienced by energetic incident electron when it is near the target.
C. transition of electron between orbit close to the atomic nucleus of the target.
D. emission of energy when target atom experiences ionisation

14. If m is the mass defect of a nucleus and E is the corresponding binding energy, which of the following
statements is correct concerning m and E ?
A. E is the kinetic energy of m. B. E is the energy equivalent of m
C. E is the binding energy of m in the nucleus. D. E is the fission energy of m from the nucleus.

15. The table below shows the count rate of a radioactive source at different times at a location.

Determine the half-life of the source based on the data given in the table.
A. 5 hours B. 10 hours C. 12 hours D. 18 hours

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Section B : [15 marks]
Answer all questions in this section.

16. In an experiment to determine the focal length of a concave mirror, an optical pin is used as an object. The
position of the optical pin in front of the concave mirror is adjusted until there is non-parallax between the
optical pin and its image formed by the mirror as seen by the eye as shown in the figure below. When this
occurs the distance of the optical pin from the concave mirror is 40.0 cm.

a) Explain the term non-parallax. [2 marks]

b) Calculate
i) the focal length, [2 marks]
ii) the radius of curvature of the concave mirror. [1mark]
c) Draw two rays from the tip of the optical pin to the concave mirror and the reflected rays. [2 marks]

17. a) Derive an expression for the number of radioactive nuclei N in a sample, at time t, in terms of the initial
number of radioactive nuclei N0 and the decay constant λ. [3 marks]
b) Technetium-99 has a half-life of 6.00 hours. It is commonly used as a radioactive tracer in medicine.
A fresh sample of 25.0 μg of technetium-99 is injected into a patient. Determine.
i) the decay constant of technetium-99. [2 marks]
ii) the activity of the tracer after 30.0 minutes. [3 marks]

Section C [30 marks] :

Answer any two questions in this section.

18. a) i) Explain what is meant by intensity of a progressive wave? [1mark]

ii) A point source emits spherical waves with a power of 5.00W. What is the intensity of the wave at the
point 20.0 m away from the source? [2 marks]

b) Stationary wave is produced along a stretched string with a wavelength of 4 cm by vibrating both ends of
the string simultaneously. The length of the string is 12 cm.
i) Draw the wave profile of the stationary wave produced. [2 marks]
ii) What is the frequency of this wave if the velocity of the wave in the string is 50 cm s -1 [2 marks]

c) The wave equation for the radio wave E1 received directly by station Y from a transmitter at station X is
given by

where E1, t and x are expressed in units of volt per metre, second, and metre respectively. A station Y also
receives radio wave E2 from a second transmitter at station X, reflected from a nearby mountain. E 2 is
equivalent to E1 except that there is a phase difference of /4
i) Determine the wavelength and frequency of the radio waves. [3 marks]
ii) Write an equation for E2 .[1 mark]
iii) Compare intensity E1 with the resultant intensity of E1 and E2 received by station Y. [4 marks]

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19. a) Explain the meaning of optical path.

b) The optical path through a glass plate and a plastic sheet are found to be the same. If the thickness of the
glass plate is 14.0 cm while the thickness of the plastic plate is 10.0 cm, compare
i) the time for a light ray to pass through the glass and the plastic [1 mark]
ii) the number of wavelengths that can be contained within the thickness of the glass and the plastic
[1 mark]
iii) the refractive indices of glass and plastic. [2 marks]

c) Monochromatic light of wavelength 480 nm is used in a Young’s two-slit experiment . The separation of
the two slits is 1.50 mm.
i) Calculate the angular separation between the interference fringes. [2 marks]
ii) When one of the two slits is covered with a transparent film with a refractive index of 1.40, the central
maximum of the interference pattern shifts to the position of the ninth bright fringe of the original
pattern. Calculate the thickness of the film. [2 marks]

d) i) What is meant by plane-polarized light? [1 mark]

ii) Explain why sound cannot be plane-polarised. [2 marks]

e) i) An unpolarised beam of intensity I0 is incident normally on a Polaroid. What is the intensity of the
transmitted beam? Explain your answer. [2 marks]
ii) The Polaroid is now rotated about the path of the ray through 90°. Describe and explain any changes
to the intensity and the plane of polarization of the transmitted light. [2 marks]

20. a) i) State a phenomenon which shows that electrons have wave properties. [1mark]
ii) In an electron microscope, electrons with de Broglie wavelength λ, is used. Derive an expression for
the potential difference required to produce electrons with wavelength λ in terms of Planck’s constant
h, mass m of the electron, charge e of the electron, and λ. If λ = 0.010 nm, calculate the potential
difference required. [5marks]
iii) State an advantage of the electron microscope over the optical microscope. [1mark]

b) i) The process of X-rays production is the inverse of that of the photoelectric effect. Explain this
statement. [2 marks]
ii) Explain the difference between the process of production of continuous X-rays with the process of
production of line X-rays from an X-ray tube. [4 marks]
iii) In an X-ray tube, electrons are accelerated by a potential difference of 10.0 kV. Calculate the
minimum wavelength for the X-rays produced. [2 marks]

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 SMJK Yu Hua, Kajang, Selangor
STPM Trial Examination
Physics Paper 3
October 2019
Mark scheme:
1. D

2. A
While X and Y have the same resonance frequency, Y (polystyrene) is lighter than X (copper). Therefore Y
will experiences greater damping effect than X and this causes its amplitude to be smaller than that of X
3. C
½ m2 (A2 – x2) = ½ m2x2
A2 – x2 = x2
2x2 = A2
x = 0.71 A
4. D
5. B
6. B

7. C
8. A

9. C
10. C

11. C

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12. C

13. C.
Each electron orbit in an atom has a fixed energy level. The transition of electrons between orbits causes the
difference in energy to be released as electromagnetic radiation
14. B
15. B

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