2004 - JAMB Physics Past Questions & Answers - page 1

1
If 16mA of current flows through a conductor in one second, the number of electron transported per seconds is
[1 electronic charge = 1.6 x 10-19C]
A
1.00 x 1020
B
2.56 x 10-18
C
2.56 x -17
D
1.00 x 1017
CORRECT OPTION: d
Current (I) = q/t → q = i x t
= 16 x 10-3 x 1
= 1.6 x 10-2C
But 1.6 x 10-19C = I electronic charge
1 coulomb = 1 / (1.6x10-19)
∴ 1.6 x 10-2 coulombs = 1 / (1.6x10-19) x 1.6x10-2 / 1
= 1.0 x 10-2 x 1019
= 1.0 x 1017
2
Electrical appliances at home are normally earthed so that
A
the appliances are maintained at a lower p.d than the earth
B
both the a.c and d.c sources can be used
C
a person touching the appliances is safe from electric shock
D
the appliances are maintained at a higher p.d than the earth
CORRECT OPTION: c
3
Given three capacitors 0.3μF, 0.5μF and 0.2μF, the joint capacitance when arranged to give minimum capacitance is
A
0.1μF
B
0.3μF
C
1.0μF
D
0.5μF
CORRECT OPTION: a
1/C = 1/0.3 + 1/0.5 + 1/0.2 = 10.3333
=> C = 1 / 10.3333 = 0.09677
≅ 0.1μF
∴ C = 0.1μF
4
The difference between X-rays and gamma rays is that
A
x-rays are more penetrating than gamma rays
B
x-rays are electromagnetic radiations while gamma rays are negatively charged radiation
C
x-rays have higher frequencies than gamma rays
D
x-rays arise from energy changes in the electronic structure of atoms while gamma rays come from the nucleus
CORRECT OPTION: d
5
To protect a material from the influnce of an external magnetic field, the materials should be kept
A
square steel ring
B
triangular zinc ring
C
soft iron ring
D
loop of copper wire
CORRECT OPTION: c
In order to protect a material from the influence of an external magnetic field, the material is placed in a soft iron ring, usually referred to as magnetic screening.
6
In the diagram above, the ratio of he electric power dissipated in the 6Ω and the 3Ω resistor respectively is
A
2:1
B
2:2
C
1:3
D
1:2
CORRECT OPTION: d
Power, P = I2R;
and I = E/R
But effective Parallel resistance: is given by:
1/R = 1/6 + 1/3 = 1+2/6 = 3/6 => R = 6/3 = 2Ω
Current I = E/R = 12/2 = 6A
But I1 = (R1/R1+R2) x 1 = 3/9 x 6 = 2A
again I1 = (R1/R1+R2) x 1 = 6/9 x 6 = 4A
∴P1 = I12 R1 = 2 x 2 x 6 = 24W
P2 = I22 R2 = 4 x 4 x 3 = 48W
thus P1/P2 = 24/48 = 1/2 ; OR P1 : P2 = 1:2
7
If the angle between two vector P and Q is Oo, the vectors are said to
A
intersect at the angle 45o
B
intersect at the angle 60o
C
be parallel
D
be perpendicular
CORRECT OPTION: c
8
A body of mass 4kg is acted on by a constant force of 12N for 3 seconds. The kinetic energy gained by the body at the end of the time is
A
144J
B
162J
C
81J
D
72J
CORRECT OPTION: b
K.E = 1/2MV2
Force, F = ma => a = F/m = 12/4 = 3ms-2
But a = (V-U) / t => V = u + at
If the initial velocity U = 0, then V = at = 3 x 3 = 9ms-2
∴ K.E, = 1/2ms-2
1/2 4 x 9 x 9 = 162J
9
A machine whose efficiency is 60% has a velocity ratio of 5. If a force of 500N is applied to lift a load P, what is the magnitude of P?
A
1500N
B
500N
C
4166N
D
750N
CORRECT OPTION: a
efficiency = (M.A / V.R) x 100/1 => 60/100 = M.A/5
∴M.A = (60 X 5) / 100 = 3
But M.A = Load/Effort; => 3 = Load/500
∴Load = 500 x 3
= 1500N
10
I. Jet propelled aircraft
II. Rocket propulsion
III. The recoil of a gun
IV. A person walking

Which of the above is based on Newton's third law of motion
A
I and II only
B
I, II, III, and IV only
C
I and III only
D
I, II and III only
CORRECT OPTION: d
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