1994 - JAMB Physics Past Questions and Answers - page 3
21
The sound from a source travelled to the bottom of the sea and the echo was heard 4s later. If the speed of sound in sea water is 1500ms-1 the depth of the sea is
A
6000m
B
3000m
C
1500m
D
375m
correct option: b
t = 4s ; v = 150ms-1
depth = X ; but 2X = vt
X = \(\frac {vt}{2}\) = \(\frac {1500 \times 4}{2}\)
X = 3000m
Users' Answers & Commentsdepth = X ; but 2X = vt
X = \(\frac {vt}{2}\) = \(\frac {1500 \times 4}{2}\)
X = 3000m
22
The fundamental frequency of vibration of a sonometer wire may be halved by
A
doubling the length of the wire
B
doubling the mass of the wire
C
reducing the tension by half
D
reducing the absolute temperature by half
23
A pipe of length 45cm is closed at the end. Calculate the fundamental frequency of the sound wave generated in the pipe if the velocity of sound in air is 360ms-1 [Neglect end correction]
A
5.5Hz
B
148.5Hz
C
200.0Hz
D
550.0Hz
correct option: c
\(\lambda\) = 4L = 4 X 45 = 180cm
F = \(\frac {V}{\lambda}\)
= \(\frac {360}{180 \times 10^{-2}}\)
= 200Hz
Users' Answers & CommentsF = \(\frac {V}{\lambda}\)
= \(\frac {360}{180 \times 10^{-2}}\)
= 200Hz
24
The note produced by a stretched string has a fundamental frequency of 400Hz. If the length of the string is doubled while the tension in the string is increased by a factor of 4, the frequency is
A
200Hz
B
400Hz
C
800Hz
D
1600Hz
correct option: b
F = \(\frac {1}{2L}\) \(\sqrt\frac{T}{m}\)
T2 = 4T1 ; L2 = 2L1
\(\frac{2F_1L_1}{2F_2L_2}\) = \(\sqrt\frac{T_1}{T_2}\)
\(\frac{400\times L_1}{F \times L_1}\) = \(\sqrt\frac{T_1}{4T_1}\)
F = 400Hz
Users' Answers & CommentsT2 = 4T1 ; L2 = 2L1
\(\frac{2F_1L_1}{2F_2L_2}\) = \(\sqrt\frac{T_1}{T_2}\)
\(\frac{400\times L_1}{F \times L_1}\) = \(\sqrt\frac{T_1}{4T_1}\)
F = 400Hz
25
To produce a parallel beam of light from a concave mirror, the distance at a which the lamp should be placed from the mirror is equal to
A
the focal length
B
two times the focal length
C
the distance of the image
D
two times the radius of curvature
correct option: a
Users' Answers & Comments26
Light of frequency 6.0 x 1014 Hz travelling in air is transmitted through glass or refractive index 1.5. Calculate the frequency of the light in the glass
A
4.0 x 1014Hz
B
6.0 x 1014Hz
C
7.5 x 1014Hz
D
9.0 x 1014Hz
27
An object is placed in front of a converging lens of a focal length 20cm. The image is virtual and has a magnification of 2. What is the distance of the object from the lens?
A
5cm
B
10cm
C
30cm
D
40cm
correct option: b
V = -2u
F = \(\frac{uv}{u + v}\)
20 = \(\frac{uv - 2u}{u - 2u}\)
u = 10cm
Users' Answers & CommentsF = \(\frac{uv}{u + v}\)
20 = \(\frac{uv - 2u}{u - 2u}\)
u = 10cm
28
An object is placed directly below a glass block of thickness 3.0cm. Calculate the lateral displacement of the object if the refractive index of the glass is 1.5.
A
1.0cm
B
1.5cm
C
2.0cm
D
2.5cm
correct option: a
1.5 = \(\frac{3}{\text {apparent displacement}}\)
Apparent depth = 2cm
displacement = 3 - 2
= 1cm
Users' Answers & CommentsApparent depth = 2cm
displacement = 3 - 2
= 1cm
29
In a projection lantern of focal length f, the object distance u, is such that
A
u > 2f > f
B
u < f < 2f
C
u = f < 2f
D
f < u < 2f
correct option: d
Users' Answers & Comments30
If the Nigeria flag (green, white, green) is viewed in pure yellow light, which of the following set of colours would be observed on the flag?
A
Green, yellow, green
B
Red, yellow, red
C
black, yellow, black
D
Green, white, green
correct option: a
Users' Answers & Comments