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Physics
UTME / JAMB 1991
Waves and Optics
Solution
Two tuning forks of frequency 256Hz and 260Hz are sounded close to each other. What is the frequency of the beats produced?
A
2Hz
B
4Hz
C
8Hz
D
258Hz
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
F = F2 - F1
= 260 - 256
= 4Hz
Source: Myschool Past Questions Archive (Record #28191)
Physics
UTME / JAMB 1991
Waves and Optics
Solution
A man hears his echo from a nearby hill 2s after he shouted. If the frequency of his voice is 260Hz and the wavelength is 1.29m, how far away is the hill?
A
330.0m
B
335.4m
C
660.0m
D
670.8m
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
v = \(\lambda\)F
260 x 1.29 =335.4ms-1
Echo time = \(\frac{2}{2}\) = 1sec.
distance = v x t
= 335.4 x 1 = 335.4m
Source: Myschool Past Questions Archive (Record #28193)
Physics
WAEC / WASSCE 1991
Waves and Optics
Which of the following is not a mechanical wave?
A
wave propagatd in stretched string
B
wave in closed pipe
C
radio waves
D
water waves
E
sound waves
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #33410)
Physics
WAEC / WASSCE 1991
Waves and Optics
Solution
Which of the following remains unchanged as light travels from one medium to the other? i. speed. ii. wavelength. iii. frequency.
A
i only
B
ii only
C
iii only
D
i and ii only
E
i and iii only
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
The frequency of the light ray remains same when it travels from one medium to another because it depends on the source of light. But the wavelength and speed vary because they depend on the medium through which the light passes.
Source: Myschool Past Questions Archive (Record #33411)
Physics
WAEC / WASSCE 1991
Waves and Optics
Which of the following statements about wave is not correct? i. A wavefront is a line which contains all particles whose vibration are in phase. ii. The direction of propagation of a wave is the link drawn parallel to the wavefront. iii. A wavefront is a circle which is common to particles that are in the same state of disturbance
A
i only
B
ii only
C
i and ii only
D
i and iii only
E
ii and iii only
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #33412)
Physics
WAEC / WASSCE 1991
Waves and Optics
Solution
A ray of light is incident at an angle of 30º on a glass prism of refractive index 1.5. Calculate the angle through which the ray is minimally deviated in the prism. (The medium surrounding the prism is air)
A
10.5o
B
19.5o
C
21.1o
D
38.9o
E
40.5o
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
n = \(\frac{sin i}{sin r}\)
sin r = \(\frac{30^o}{n}\)
sin r = \(\frac{0.5}{1.5}\)
sin r = 0.3333
r = sin\(^{-1}\)(0.333) = 19.5º
At minimum deviation, the ray passes symmetrically, so A = 2r
A = 2 x 19. 5 = 38.94
But minimum deviation = 2i - A
= 2 x (30º) - 38.94 = 21.06º
:
Source: Myschool Past Questions Archive (Record #33400)
Physics
WAEC / WASSCE 1991
Waves and Optics
Solution
Which of the following are true of plane-polarised light? i. Plane polarisation of light is the formation of hydrogen bubbles on the particle of light. ii. Plane polarisation of light is the splitting of light into its spectral components iii. A plane polarised light vibrates in one plane. iv. Polarisation of light is characteristic of transverse vibration
A
i and ii only
B
i and iv only
C
ii and iii only
D
iii and iv only
E
i and iii only.
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
Plane-polarized light consists of waves that vibrate in a single plane. Polarization occurs in transverse waves, where the oscillations are perpendicular to the direction of wave propagation.
Source: Myschool Past Questions Archive (Record #33407)
Physics
WAEC / WASSCE 1991
Waves and Optics
At which of the following distances from the lens should a slide be placed on a slide projector if f is the focal length of the projector length?
A
less than f
B
greater than f but less than 3f
C
equal to f
D
equal to 2f
E
greater than 2f
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #33408)
Physics
WAEC / WASSCE 1991
Waves and Optics
Diagram
Two mirrors are inclined as shown in the diagram. A ray of light RO strikes the arrangement at O and emerges along PO. The emergent ray has been deviated through
Attached Figure / Diagram
A
240o
B
180o
C
120o
D
60o
E
30o
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #33396)
Physics
WAEC / WASSCE 1991
Waves and Optics
Diagram
In the arrangement illustrated above, Y and B are yellow and blue transparent light filters respectively through the filters is
Attached Figure / Diagram
A
blue
B
red
C
yellow
D
green
E
black
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #33397)
Physics
WAEC / WASSCE 1991
Waves and Optics
The sound from a bell in an enclosed jar gradually faints away while the jar is being evacuated. Which of the following explains this observation?
A
the pressue is reduced
B
the sound waves are pumped out
C
the waves are absorbed in the inner walls
D
There is no more material medium
E
the air is disturbed
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #33414)
Physics
WAEC / WASSCE 1991
Waves and Optics
In which of the following is a stationary wave produced? i. A vibrating turning fork held near the end of a resonance tube closed at one end. ii. A string tightly stretched between two points and plucked at its middle. iii. The tuning fork vibrating in air
A
i only
B
ii only
C
i and ii only
D
ii and iii only
E
i, ii and iii
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #33417)
Physics
WAEC / WASSCE 1991
Waves and Optics
Diagram
Solution
If the frequency of the e.m.f. source in the a.c. circuit illustrated above is \(\frac{500}{\pi}\)Hz. What is the reactance of the inductor?
Attached Figure / Diagram
A
450
B
0.9
C
900
D
567
E
43
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
x = 2\(\pi f L = 2\pi \times \frac{500}{\pi} \times 0.9\)
= 900\(\Omega\)
Source: Myschool Past Questions Archive (Record #33423)
Physics
WAEC / WASSCE 1991
Waves and Optics
Solution
(a) Explain the terms reactance and impedance in an a.c circuit.
(b) A source of e.m.f. 240 v and frequency 50 Hz is connected to a resistor, an inductor and a capacitor in series. When the current in the capacitor is 10A, the potential difference across the resistor is 140V and that across the inductor is 50V. Draw the vector diagram of the potential difference across the inductor, the capacitor and the resistor.
Calculate the (i) potential difference across the capacitor; (ii) capacitance of the capacitor; (iii) inductance of the inductor.
medium Difficulty
Verified Correct Answer: Option
Physical Principles & Numerical Solution
(a) Reactance is the opposition in ohms to th alternating current by a capacitor or inductor. It is defined by
\(X_{C} = \frac{V}{I}\) or \(X_{L} = \frac{V}{I}\)
\(X_{C} = \frac{1}{2 \pi f c}\) or \(X_{L} = 2 \pi fl\)
V - voltage (V), c - current, f - frequency (Hz), I - inductance (H), c - capacitance (F).
Impedance is the opposition in ohms to the alternating current by combination of resistor, inductor or capacitor. It is defined as:
Z = \(\sqrt{R^{2} + X_{L} ^{2}}\)
Z = \(\sqrt{R^{2} + X^{2}}\)
Z = \(\sqrt{R^{2} + (X_{C} - X_{L})^{2}}\)
(b)
Hence using ,
\(V = \sqrt{V_{R} ^{2} + (V_{L} - V_{C})^{2}}\)
\(240 = \sqrt{140^{2} + (50 - V_{C})^{2}}\)
Square both sides,
\(57600 = 19600 + (50 - V_{C})^{2} \implies 57600 - 19600 = (50 - V_{C})^{2}\)
\(38000 = (50 - V_{C})^{2}\)
\(\sqrt{38000} = 50 - V_{C}\)
\(\pm 194.936 = 50 - V_{C} \implies V_{C} = \pm 194.936 + 50\)
\(V_{C} = -144.936 ; V_{C} = 244.936v\)
The voltage cannot be negative, hence, \(V_{C} = 244.936v\)
(ii) Using \(X_{C} = \frac{1}{2 \pi fc} = \frac{V}{I}\)
\(\frac{244.936}{10} = \frac{1}{2\pi \times 50 \times c}\)
\(24.4936 = \frac{1}{2\pi \times 50 \times c} \implies c = \frac{1}{2\pi \times 50 \times 24.4936}\)
\(c = \frac{1}{7694.89} = 0.00013F = 130\mu F\)
Source: Myschool Past Questions Archive (Record #54775)
Physics
WAEC / WASSCE 1990
Waves and Optics
When the direction of vibration of the particles of a medium is perpendicular to the direction of travel of a wave the wave transmitted is known as
A
sound wave
B
transverse wave
C
longitudinal wave
D
stationary wave
E
mechanical wave
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #24101)