# 2009 - JAMB Physics Past Questions & Answers - page 1

1
The ability of the human eye to focus object on the retina is referred to as the power of
A
interference
B
diffraction
C
accomodation
D
superposition
CORRECT OPTION: c
The leaves collapse as the position charges on the rod neutralize the negative charges on the electroscope
2
Which of the following is a secondary colour
A
blue
B
orange
C
red
D
green
CORRECT OPTION: b
Primary colours are red, blue and green
∴ orange is a secondary colour
3
If negative charges are induced on an electroscope and a positively charged rod is brought near the cap of the electroscope, the leaves will
A
close up
B
become positively charged
C
become negatively charged
D
open further
CORRECT OPTION: a
The leaves collapse as the positive charges on the rod neutralize the negative charges on the electroscope.
4
An electric lamp marked 240v, 60 W is left to operate for an hour. How much energy is generated by the filament?
A
3.86 x 105J
B
3.56 x 105J
C
1.80 x 104J
D
2.16 x 105J
CORRECT OPTION: d
Energy generated = power X time = 60w x 1h = 60 x 60 x 60 ws = 216000j = 2.16 x 105J
5
A band of 500 rectangular loops of wire of area 20 cm by 20 cm, encloses a region of magnetic field which charges from 1.0T to 0.4T within 5 seconds, calculate the induced e.m.f.
A
5.60 v
B
24.00 v
C
0.24 v
D
2.40 v
CORRECT OPTION: d
Number of tunes, n = 500
Area, A = 0.2m + 0.2m = 0.4m2
change of flux density A B
= 1.0 - 0.4 = 0.6T
Tune, t = 5 su
Induced emf, ξ = (AB AN)/AT
(0.6 x 0. 04 x 500)/5
= 2.4v
6
Cancerous cells can be destroyed by
A
ultraviolet rays
B
alpha particules
C
x - rays
D
infrared rays
CORRECT OPTION: c
Canorous cells can be destroyed with a high penetrating radiation which is x - rays
7
If the decay constant of a radioactive substance is 0.231s1, the half-life is?
A
3.00 s
B
0.12 s
C
0.33 s
D
1.50 s
CORRECT OPTION: a
Half-life, T (1)/2 = (0.693)/∆ = (0.693)/ 0.231 = 3.0sec
8
A piece of radioactive material contains 1020 atoms.
If the half life of the material is 20 seconds, the number of disintegration in the first second is
A
3.47 x 1018
B
6.93 x 10 20
C
3.47 x 1020
D
6.93 x 1018
CORRECT OPTION: a
The number of disintegration,∆N in time interval At, is given by
- ∆N = N∆t
Where N is the number of atoms present at the time t
But ^ = (0.693)/T
∴ ∆N = (0.693)/1(1)/2 N∆t = (0.693 x 10)20 x 10/20 = 3.47 x 1018
9
Thermionic emission is the process whereby
A
β - rays are produced
B
holes are produced
C
x - rays are produced
D
electrons leave a hot element
CORRECT OPTION: d
Thermionic emission is ejection of electron from a metal surface as a result of heating.
10
Which of the following can conduct electricity owing to the presence of free mobile electrons?
A
germanium
B
silicon
C
grapefruit
D
copper
CORRECT OPTION: d
Metals are good conductors due to the presence of free electrons
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