2011 - JAMB Physics Past Questions and Answers - page 5
41
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
Users' Answers & Comments42
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
Users' Answers & Comments| V = | w | = | Fr | = | Q1Q2 | x | r |
| Q | Q | 4πεor2 | Q1 |
| = | _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
Users' Answers & Commentsv = -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
= 306Hz
Users' Answers & Commentsf2 = ? 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
A
14.4 A
B
1.0 A
C
3.2 A
D
9.6 A
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
Users' Answers & Comments\( P \propto \frac{1}{v} \) 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.
Users' Answers & Comments48
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 = \( \frac{I_0}{\sqrt{2}} \)
\( \text{Therefore } \sqrt{2Irms} = I_0 \\
\frac{Irms}{I_0} = \frac{1}{\sqrt{2}} \)
Users' Answers & Comments\( \text{Therefore } \sqrt{2Irms} = I_0 \\
\frac{Irms}{I_0} = \frac{1}{\sqrt{2}} \)
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