2004 - JAMB Physics Past Questions and Answers - page 4

31
Transverse waves can be distinguished from longitudinal waves using the characteristic of
A
diffraction
B
refraction
C
polarization
D
reflection
correct option: c
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32
A man exerts a pressure of 2.8 x 103Nm-2 on the ground and has 4 x 10-2m2 of his feet in contact with the ground. The weight of the man is
A
102N
B
70N
C
140N
D
112N
correct option: d

Pressure = Force / Area = Weight of the man / Area of his feet

=> 2.8 x 103 = Weight of the man / 4 x 10-2

∴ Weight of the man = 2.8 x 103 x 4 x 10-2

= 112N

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33
Calculate the angle of minimum deviation for a ray which is refracted through an equiangular prism of refractive index 1.4
A
600
B
290
C
990
D
900
correct option: b

From the relation refractive index = Sin ( \left(\frac{A+Dm}{2}\right) )

Where A = refractive angle = 600, Sin( \left(\frac{A}{2}\right) )

( \implies 1.4 = \frac{\text{Sin}\left(\frac{60^0 + Dm}{2}\right)}{\text{Sin}\left(\frac{60}{2}\right)} \

= \frac{\text{Sin}\left(\frac{60 + Dm}{2}\right)}{\text{Sin}30^0} \

= \frac{\text{Sin}\left(\frac{60 + Dm}{2}\right)}{0.5}\

\text{Therefore} 1.4 \times 0.5 = \text{Sin}\left(\frac{60 + Dm}{2}\right) \

\text{Therefore} \left(\frac{60 + D_m}{2}\right)= \text{Sin}^{-1} 0.7000 \

= 44^0 12^1 \

60^0 + D_m = 88^0 24^1 \

D_m = 88^0 24^1 - 60^0 \

= 28^0 24 \

29^0 )

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34
A cell whose internal resistance is 0.5Ω delivers a current of 4A to an external resistor,The loss voltage of the cell is
A
1.250V
B
2.000V
C
8.000V
D
0.125V
correct option: b

E = V + v

where E = emf of cell.

V = terminal p.d

v = loss voltage of the cell.

But from ohm's law V=IR ; v = Iv

( \implies ) lost voltage = V = Ir

= 4 x 0.5

= 2.0v

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35
If a force of 50N stretches a wire from 20m to 20.01m, what is the amount of force required to stretch the same material from 20m to 20.05m?
A
250N
B
200N
C
100N
D
50N
correct option: a

Original length = 20m

first new length = 20.01m

first increase in length = 20.01m - 20m = 0.01m

Second new length = 20.05m

second increase in length = 20.05 - 20m = 0.05m

From hooke's law = ( \frac{F_1}{e_1} = \frac{F_2}{e_2} \implies \frac{50}{0.01} = \frac{F_2}{0.05} \

\implies F_2 = \frac{50 \times 0.05}{0.01} = 250N )

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36
A generator manufacturing company was contracted to produce an a.c dynamo but inadvertently produced a d.c dynamo. To correct this error, the
A
armature coil should be made of silver
B
commutator should be replaced with slip ring
C
commutator should be replaced with split rings
D
armature coil should be made of aluminium
correct option: b
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37
A radioisotope has a decay constant of 10-7s-1. The average life of the radioisotope is
A
1.00 x 107s
B
6.93 x 108s
C
1.00 x 10-7s
D
6.93 x 107s
correct option: b

Average life / Half life (Tl/2) = ln2/λ = 0.693/10-7

= 0.693 x 107

= 6.93 x 108

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38
An a.c circuit of e.m.f 12V has a resistor of resistance 8Ω connected in series to an inductor of inductive reactance 16Ω and a capacitor capacitive reactance 10Ω. The current flow in the circuit is
A
1.4A
B
1.2A
C
12.0A
D
14.0A
correct option: b

Current (I) in the circuit = V/Z
But z =

 R2 + (XL - XC)2 

=

 82 + (16 – 10) 2 

=

 64 + 36 

=

 100  = 10Ω

∴ Current (I) = V/Z = 12/10 = 1.2 A

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39
For semi conductor to have negative temperature coefficient of resistance implies that
A
their resistance decrease with temperature
B
The resistance increase with temperature
C
their resistance is constantly changing with temperature
D
they have electrons and holes at high temperature
correct option: a

Temperature coefficient of resistance is given by

α = Increase in resistance per oC rise in temp.
__resistance at 0oC

And for metals where resistance increase with temperature rise, temperature coefficient of resistance is positive; on the other hand in semi conductors, where resistance decrease with temperature rise, temperature coefficient of resistance is negative.

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40
X rays can be used in the study of crystal structure because they
A
have a very long-reaching wavelength
B
have extremely short wavelength
C
are invisible
D
are very fast
correct option: b
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