2001 - JAMB Physics Past Questions and Answers - page 4
31
The process of energy production in the sun is
A
nuclear fission
B
nuclear fussion
C
electron collision
D
radioactive decay
correct option: b
The process of energy production in the sun is generally by nuclear fusion of hydrogen nuclei, the reaction of which takes place at a tremendous high temperature of the order of 107K.
H1 + H1 2H
Users' Answers & CommentsH1 + H1 2H
32
At reasonance, the phase angle in an a.c. circuit is
A
90°
B
60°
C
0°
D
180°
correct option: c
At reasonance in an a.c. circuit, during which the capacitive reactance Xc is equal to the inductive reactance Xl, the phase angle Ø = 0°
Users' Answers & Comments33
The force on a current carrying conductor in a magnetic field is greatest when the
A
conductor makes an angle of 60° with the field
B
force is idependent of the angles between the fields and the conductor
C
conductor is parallel with the field
D
conductor is at right angle with the field
correct option: d
The force on a current carrying conductor in a
magnetic field is greatest when the conductor lies perpendicular in the magnetic field
Users' Answers & Commentsmagnetic field is greatest when the conductor lies perpendicular in the magnetic field
34
A transistor function mainly as a
A
switch and amplifier
B
rectifier and an amplifier
C
charge storer and an amplifier
D
charge storer and a switch
correct option: a
Users' Answers & Comments35
Energy losses through eddy currents are reduced by using
A
low resistance wires
B
insulated soft iron wires
C
few turns of wires
D
high resistance wires
correct option: b
Users' Answers & Comments36
A capacitor of 20 x 10-12F and an inductor are joined in series. The value of the inductance that will give the circuit a resonance frequency of 200kHz is
A
I/16 H
B
I/8 H
C
I/64 H
D
I/32 H
correct option: d
Resonant, frequency in an a.c. circuit is given by F = I/2π√LC
therefore 200 * 103 = I/2 * π√l * 20 * 10-12
therefore (2.0 * 105)2 = I/4 * π2 * L * 20 * 10-12
THEREFORE L = I/4.0 * 1010 * 4 * 10 * 20 * 10-12
(if π2 = 10)
= I/16 * 1011 * 2.0 * 10-11
Therefore L = I/32 H
Users' Answers & Commentstherefore 200 * 103 = I/2 * π√l * 20 * 10-12
therefore (2.0 * 105)2 = I/4 * π2 * L * 20 * 10-12
THEREFORE L = I/4.0 * 1010 * 4 * 10 * 20 * 10-12
(if π2 = 10)
= I/16 * 1011 * 2.0 * 10-11
Therefore L = I/32 H
37
The magnetic force on a charged particle moving with velocity v is
A
proportional to both the magnitude of the charge and the velocity v
B
independent of the magnitude of the charge
C
proportional to the velocity v only
D
proportional to the magnitude of the charge only
correct option: a
The magnetic force on a charge is given by
F = qVB Sinθ,
thus the force is proportional to both the magnitude by the charge (q) and the velocity (V)
(i/e F α qV)
Users' Answers & CommentsF = qVB Sinθ,
thus the force is proportional to both the magnitude by the charge (q) and the velocity (V)
(i/e F α qV)
38
A
T
B
U
C
R and T
D
Q and R
correct option: a
The pendulum that will resonate with P is T. being of the same length and therefore of the same frequency.
Users' Answers & Comments39
A
60%
B
50%
C
40%
D
33%
correct option: b
Since the number of pulleys present is 6, it implies that the velocity ratio VR = 6
= Load/Effort x 1/V.R x 100/1
= 240/80 x 1/6 x 100/1
= 50%
∴ Efficiency = 50%
Users' Answers & Comments| ∴ efficiency = | M.A |
| |||
| V.R |
= Load/Effort x 1/V.R x 100/1
= 240/80 x 1/6 x 100/1
= 50%
∴ Efficiency = 50%
40
A
cosα / sinβ
B
sinα / sinβ
C
cosβ / sinα
D
sinβ / sinα
correct option: a
| From the diagram above, refractive index of the medium = | sin(90- α ) |
| _sin β |
| Reflective index of the medium = | cos α |
| sin β |