2004 - JAMB Physics Past Questions and Answers - page 3
21
The pitch of a sound note depends on
A
timbre
B
frequency
C
harmonics
D
quality
correct option: b
Users' Answers & Comments22
If u is the object distance and v the image distance, which of the following expressions gives the linear magnification produced by a convex lens of focal length f?
A
u/f - f
B
u/v + f
C
v/f + 1
D
v/f - 1
correct option: d
Magnification, M = v/u = v (1/u)
And for the Lens formula 1/u + 1/v = 1/f
=> 1/u = 1/f - 1/v
∴M = V(1/u)
= V(1/f - 1/v) = v/f - v/v = v/f - 1
∴M = v/f - 1
Users' Answers & CommentsAnd for the Lens formula 1/u + 1/v = 1/f
=> 1/u = 1/f - 1/v
∴M = V(1/u)
= V(1/f - 1/v) = v/f - v/v = v/f - 1
∴M = v/f - 1
23
A
1/√3
B
2√3
C
√3
D
2/√3
correct option: c
From the above diagram ; ? = 90o - 30o = 60o
v = 90 - 60 = 30
∴ refractive index = (sin ?)/(sin v) = (sin 60o / sin 30o) = √3/2/1/2
= √3/2 x 1/2
= √3
Users' Answers & Commentsv = 90 - 60 = 30
∴ refractive index = (sin ?)/(sin v) = (sin 60o / sin 30o) = √3/2/1/2
= √3/2 x 1/2
= √3
24
When left in a freezer, a bottle full of water cracks on freezing into ice because of the
A
increase in the volume of water
B
contraction of the bottle
C
expansion of the bottle
D
decrease in the volume of water
correct option: a
Users' Answers & Comments25
A
2π
B
π
C
π/4
D
π/2
correct option: d
Users' Answers & Comments26
The change in volume when 450kg of ice is completely melted is
[density of ice = 900 kgm-3, density of water = 100 kgm-3]
[density of ice = 900 kgm-3, density of water = 100 kgm-3]
A
0.50m3
B
0.45m3
C
0.05m3
D
4.50m3
correct option: c
Vol. of ice = M/?D = 450/900 = 0.500m3
vol. of water = M/D" = 450/1000 = 0.450m3
∴ Difference in vol. = 0.500 - 0.450
= 0.05m3
Users' Answers & Commentsvol. of water = M/D" = 450/1000 = 0.450m3
∴ Difference in vol. = 0.500 - 0.450
= 0.05m3
27
Tea pots are often silver-coated to prevent heat loss by
A
conduction only
B
convention only
C
convection and conduction
D
radiation only
correct option: d
Users' Answers & Comments28
I. Wavelength
II. Medium of propagation
III. Wave velocity
IV. Frequency
V. Energy
Which of the above are used for characterizing waves?
II. Medium of propagation
III. Wave velocity
IV. Frequency
V. Energy
Which of the above are used for characterizing waves?
A
I, II and V
B
I and IV
C
I, III and IV
D
III, IV and V
correct option: c
Users' Answers & Comments29
A 50W electric heater is used to heat a metal block of mass 5kg. If in 10 minutes a temperature rise of 12oC is achieved, the specific heat capacity of the metal is
A
400 J kg-1K-1
B
500 J kg-1K-1
C
390 J kg-1K-1
D
130 J kg-1K-1
correct option: b
Heat supplied by the heater in 10 mins
= power x time
= 50 x (10 x 60)
= 30000 J
This heat is equal = MCΔt
= 5 x c x 12
= 60cJ
= 60C = 30,000
C = 30,000/60
C = 500 J kg-1K-1
Users' Answers & Comments= power x time
= 50 x (10 x 60)
= 30000 J
This heat is equal = MCΔt
= 5 x c x 12
= 60cJ
= 60C = 30,000
C = 30,000/60
C = 500 J kg-1K-1
30
Metal rods of length 20m each are laid end to end to form a bridge at 25oC. What gap will be provided between consecutive rails for the bridge to withstand 75oC?
[Linear expansivity of the material = 2.0 x 10-5K-1
[Linear expansivity of the material = 2.0 x 10-5K-1
A
0.20m
B
0.22m
C
0.25m
D
0.02m
correct option: d
Safety gap = expansion of the rod
= ∝Lo Δ t
= 2.0 x 10-5 x 20 x (75 - 25)
= 2.0 x 10-5 x 20 x 50
= 2.0 x 10-5 x 103
= 2.0 x 10-2 OR 0.02m
Users' Answers & Comments= ∝Lo Δ t
= 2.0 x 10-5 x 20 x (75 - 25)
= 2.0 x 10-5 x 20 x 50
= 2.0 x 10-5 x 103
= 2.0 x 10-2 OR 0.02m