1998 - WAEC Physics Past Questions and Answers - page 4
31
A lantern gives an image of 3m square of a slide 7.62cm square on a screen. If the screen is 10m from the projection lens of the lantern, calculate the focal length of the lens
A
40.3cm
B
26.1cm
C
24.8cm
D
0.7cm
correct option: c
M = \(\frac{V_H}{U_H} = \frac{300}{7.62}\)
= 39.3
U = \(\frac{V}{M} = \frac{1000}{39.3}\) = 25.44
\(\frac{1}{f} = \frac{I}{U} + \frac{I}{V} = \frac{I}{25.44} = \frac{I}{1000} = \frac{1025.44}{25440}\)
f = \(\frac{25440}{1025.44} = 24.8\)
Users' Answers & Comments= 39.3
U = \(\frac{V}{M} = \frac{1000}{39.3}\) = 25.44
\(\frac{1}{f} = \frac{I}{U} + \frac{I}{V} = \frac{I}{25.44} = \frac{I}{1000} = \frac{1025.44}{25440}\)
f = \(\frac{25440}{1025.44} = 24.8\)
32
The intensity of light falling on the film in a camera depend on the i. brightness of the object. ii. diameter of the aperture stop. iii. speed of the shutter. Which of the statements is/are correct/
A
i, ii and iii
B
i and ii only
C
i and ii only
D
ii and iii only
correct option: e
Users' Answers & Comments33
the shortest length of the air column in a resonance tube at resonance is 0.12m and the next resonance length is 0.37m. calculate the frequency of vibration given that the speed of sound in air is 340m-1
A
1360Hz
B
694Hz
C
680Hz
D
34Hz
correct option: c
f = \(\frac{v}{2(l_2 - l_1)} = \frac{340}{2(0.37 - 0.12)} = \frac{34}{0.5}\) = 680
Users' Answers & Comments34
A sonometer wire under a tension of N10N, produces a frequency of 250Hz when plucked. Keeping the length of the wire constant, the tension is adjusted to produce a new frequency of 350Hz. Calculate the new tension
A
39.2N
B
19.6N
C
14.2N
D
7.4N
correct option: b
f \(\alpha\) \(\sqrt{T}\)
\(\frac{f_1}{f_2} = \sqrt{\frac{T_1}{T_2}}\)
\(\frac{250}{350} = \sqrt{\frac{10}{T_2}}\)
\(\frac{5}{7} = \sqrt{\frac{10}{T_2}}\)
\(\frac{25}{49} = \frac{10}{T_2}\)
T2 = \(\frac{49 \times 10}{25} = 19.6\)
Users' Answers & Comments\(\frac{f_1}{f_2} = \sqrt{\frac{T_1}{T_2}}\)
\(\frac{250}{350} = \sqrt{\frac{10}{T_2}}\)
\(\frac{5}{7} = \sqrt{\frac{10}{T_2}}\)
\(\frac{25}{49} = \frac{10}{T_2}\)
T2 = \(\frac{49 \times 10}{25} = 19.6\)
35
Calculate he wavelength of a note which is one octave lower than a note of 256Hz in a medium in which the speed of sound is 352ms-1
A
0.69m
B
1.38m
C
2.75m
D
5.50m
36
Which of the following are both mechanical and transverse?
A
infra-red rays
B
gamma rays
C
sound waves
D
water waves
correct option: d
Users' Answers & Comments37
An electromagnetic wave of frequency 5.0 x 1014Hz, is incident on the surface of water of refractive index \(\frac{4}{3}\). Taking the speed of the wave in air as 3.0 x 108ms-1, calculate the wavelength of the wave in water.
A
2.2 x 10-6m
B
1.7 x 10-7m
C
8.0 x 10-7m
D
6.0 x 10-7m
correct option: e
\(_an_w = \frac{\lambda_a}{\lambda_w}\)
\(\frac{4}{3} = \frac{\lambda_a}{\lambda}\)
\(\lambda_w = \frac{v}{f}\)
= \(\frac{3.0 \times 10^8}{5.0 \times 10^{14}} = 0.6 \times 10^{-6}\)
\(\lambda_w = \frac{3}{4} \lambda_a = \frac{3}{4} \times 0.6 \times 10^{-6}\)
= 4.5 x 10-7m
Users' Answers & Comments\(\frac{4}{3} = \frac{\lambda_a}{\lambda}\)
\(\lambda_w = \frac{v}{f}\)
= \(\frac{3.0 \times 10^8}{5.0 \times 10^{14}} = 0.6 \times 10^{-6}\)
\(\lambda_w = \frac{3}{4} \lambda_a = \frac{3}{4} \times 0.6 \times 10^{-6}\)
= 4.5 x 10-7m
38
The gravitational force of the moon is one-sixth that of the earth. If a body weighs 6.0N on the moon. Calculate its weight on the earth
A
36.0N
B
12.0N
C
6.0N
D
2.0N
39
In the electrical method of magnetisation, the polarity of the magnet depends on the
A
amount of current passed
B
direction of current
C
magnetic material used
D
size of the magnetic material
correct option: b
Users' Answers & Comments40
A cell of e.m.f. 1.5v is connected in series with a resistor of 3\(\Omega\). A high resistance voltmeter connected across the cell registers only 0.9v. Calculate the internal resistance of the cell
A
5.0\(\Omega\)
B
4.5\(\Omega\)
C
2.4\(\Omega\)
D
2.0\(\Omega\)
correct option: a
I = \(\frac{V}{R} = \frac{0.9}{3} = 3\)
r = \(\frac{E}{I} = \frac{1.5}{0.3} = 5\)
Users' Answers & Commentsr = \(\frac{E}{I} = \frac{1.5}{0.3} = 5\)