2011 - JAMB Physics Past Questions & Answers - page 5

41
The diagram above show the positions of a cone. The position which can be described as neutral equilibrium is represented as
A
Z only
B
X only
C
Y and Z
D
Y and X
CORRECT OPTION: a
Under neutral equilibrium, the body rolls and the position of the center of gravity , C. G is neither raised nor lowered
42
The correct expression for the potential at a point distance r from a charge q in an electric field is
A
_q2
4πεor2
B
_q2
4πεor
C
_q
4πεor2
D
_q
4πεor
CORRECT OPTION: d
Electric potential is work done in taking a unit mass or charge from infinity to that point
V = w = Fr = Q1Q2 x r
QQ4πεor2Q1

= _q
4πεor
43
An image in a convex lens is upright and magnified 3 times. If the focal length of the lens is 15 cm, what is the object distance?
A
10 cm
B
25 cm
C
16 cm
D
14 cm
CORRECT OPTION: a
m = v/u = -3
v = -3u
f = 15cm
1/v + 1/U = 1/f
1/-3U + 1/u = 1/15
2/3u = 1/15
3U = 15 x 2
U = 30/3
= 10 cm
44
A length of wire has a frequency of 255Hz when stretched by a force of b225N. If the fore increased to 324N, what is the new frequency of vibration
A
306 Hz
B
512 Hz
C
488 Hz
D
356 Hz
CORRECT OPTION: a
f1 = 255Hz, T1 = 225N
f2 = ? T2 = 324N
But f ∝ √T => f = K√T
=> K = f/√T
f1/√T1 = f2/√T2
225/√225 = f2/√324
f2 = 225√225
√225


= 225 x 18
__15

= 306Hz
45
In the circuit above, three resistors, 2Ω, 4Ω and 12Ω are connected in parallel and a 12V battery is connected across the combination. The current flowing through the 12Ω resistors is
A
14.4 A
B
1.0 A
C
3.2 A
D
9.6 A
CORRECT OPTION: b
IV
R

= 12
12

= 1A
46
If the volume of a gas increases steadily as the temperature decreases at constant pressure, the gas obeys
A
Graham's Law
B
Boyle's Law
C
Pressure law
D
Charles Law
CORRECT OPTION: e
Correct Answer: Option E Rate of diffusion is inversely proportional to the square root of density - Graham's law

\( P \propto \frac{1}{v} \) at constant temperature - Boyle's law

\( P \propto T \) at constant volume - Pressure law

\( P \propto T \) at constant pressure - Charles law

therefore no correct option
47
In Homes, electrical appliances and lamps are connected in parallel because
A
Parallel connections do not heat up the wires
B
series connections use high voltage
C
less current will be used
D
less voltage will be used
CORRECT OPTION: b
if appliances are connected in series, the effective voltage is the sum of individual voltages which will be high.
48
In an A.C circuit, the ratio of r.m.s value to peak value of current is
A
2
B
\( \frac{1}{2} \)
C
\( \frac{1}{\sqrt{2}} \)
D
\( \sqrt{2} \)
CORRECT OPTION: c
Irms = \( \frac{I_0}{\sqrt{2}} \)

\( \text{Therefore } \sqrt{2Irms} = I_0 \\
\frac{Irms}{I_0} = \frac{1}{\sqrt{2}} \)
49
Two resistors 5Ω and 10Ω are arranged first in series and later in parallel to a 24V source, the ratio of total power dissipated in the series and parallel arrangements respectively is
A
5:3
B
1:50
C
50:1
D
3:5
CORRECT OPTION: e
Correct Answer: Option E
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