1990 - JAMB Physics Past Questions and Answers - page 3
21
A boy looks at the image of an object in a plane mirror. He observes two images, a main bright one and the other faint. The observed images result from
A
reflection only
B
refraction only
C
diffraction and interference
D
reflection and refraction
correct option: a
Users' Answers & Comments22
What must be the distance between an object and a converging lens of focal length 20cm to produce an erect image two times the object height?
A
20cm
B
15cm
C
10cm
D
5cm
correct option: c
F = \(\frac{uv}{u + v}\); v = 2u
20 = \(\frac{ux - 2u}{u + (-2u)}\); u = 10cm
Users' Answers & Comments20 = \(\frac{ux - 2u}{u + (-2u)}\); u = 10cm
23
For a short sighted person, light rays from a point on a very distant object is focused
A
in front of the retina
B
on the retina by a converging lens
C
behind the retina by a diverging lens
D
in front of the retina, a distance 2F from the lens
correct option: a
Users' Answers & Comments24
When light is incident on an object which is magenta in colour, which of the following colour would be absorbed?
A
Red and blue
B
Green only
C
Red and green
D
Red only
correct option: b
Users' Answers & Comments25
In a resonance tube experiment, the effective length of the air column for the first resonance is 20cm when set into vibration by a tuning fork of frequency 480Hz. Neglecting and effect, the velocity of sound in air is
A
96ms-1
B
255ms-1
C
340ms-1
D
384ms-1
correct option: d
\(\lambda\) = 4(L + C) ; where C = o
\(\lambda\) = 4 x 20 = 80cm
V = \(\lambda\)F
= 80 x 10-2 x 480 = 384ms-1
Users' Answers & Comments\(\lambda\) = 4 x 20 = 80cm
V = \(\lambda\)F
= 80 x 10-2 x 480 = 384ms-1
26
An organic pipe closed at one end is 80cm long. Determine the frequency of the fundamental note assuming that the speed of sound in air is 340ms-1
A
106Hz
B
213Hz
C
318Hz
D
425Hz
correct option: a
\(\lambda\) = 4L
= 4 x 80 = 320cm
F = \(\frac{V}{\lambda}\)
= \(\frac{340}{34 \times 10^2}\)
= 106Hz
Users' Answers & Comments= 4 x 80 = 320cm
F = \(\frac{V}{\lambda}\)
= \(\frac{340}{34 \times 10^2}\)
= 106Hz
27
A sonometer wire of length 100cm under a tension of 10N, has a frequency of 250Hz. Keeping the length of the wire constant, the tension is adjusted to produce a new frequency of 350Hz. The new tension is
A
5.1N
B
7.1N
C
14.0N
D
19.6N
correct option: d
\(\frac{F_1}{F_2}\) = \(\sqrt\frac{T_1}{T_2}\)
\(\frac{250}{350}\) = \(\sqrt\frac{10}{T_2}\)
T2 = 19.6N
Users' Answers & Comments\(\frac{250}{350}\) = \(\sqrt\frac{10}{T_2}\)
T2 = 19.6N
28
One of the properties of the earth's magnetic field is that the
A
north pole lies in the northern hemisphere
B
geographic and magnetic meridians coincide
C
earth's magnetic flux is entirely horizontal at a place where the magnetic dip is zero
D
earth's magnetic flux is entirely vertical at a place where the magnetic dip is zero
correct option: c
Users' Answers & Comments29
Which of the following statements are true of an insulated charged body carrying positive charge? i. it contains excess positive charges. ii. it creates an electric field. iii. it possesses potential energy. iv. it carries electric current.
A
i and iv only
B
i and ii only
C
i, ii, iii only
D
i, ii, iii and iv
correct option: d
Users' Answers & Comments30
Which of the following is a vector?
A
Electric charge
B
Electric field
C
Electrical potential difference
D
Electrical capacitance
correct option: b
Users' Answers & Comments