1990 - JAMB Physics Past Questions and Answers - page 4
31
Three cells each of e.m.f. 1.5v and an internal resistance of 1.0\(\Omega\) are connected in parallel across a load resistance of 2.67\(\Omega\). Calculate the current in the load?
A
0.26A
B
0.41A
C
0.50A
D
0.79A
correct option: c
E = 1.5v
rT = \(\frac{1 \times 1\times 1}{(1\times1)+ (1\times1) +(1\times1)}\)
E.m. f = I(R + r) = 0.33\(\Omega\)
1.5 = I(2.67 + 0.33)
I = 0.5A
Users' Answers & CommentsrT = \(\frac{1 \times 1\times 1}{(1\times1)+ (1\times1) +(1\times1)}\)
E.m. f = I(R + r) = 0.33\(\Omega\)
1.5 = I(2.67 + 0.33)
I = 0.5A
32
When a known standard resistor of 2\(\Omega\) is connected to the 0.0cm end of a meter bridge, the balance point is found to be at 55.0cm. What is the value of the unknown resistor?
A
1.10\(\Omega\)
B
1.64\(\Omega\)
C
2.44\(\Omega\)
D
27.50\(\Omega\)
correct option: b
\(\frac{R_1}{R_2}\) = \(\frac{L_1}{R_2}\)
\(\frac{2}{R_2}\) = \(\frac{55}{45}\)
R = 1.64\(\Omega\)
Users' Answers & Comments\(\frac{2}{R_2}\) = \(\frac{55}{45}\)
R = 1.64\(\Omega\)
33
The total energy required to send a unit positive charge round a complete electrical circuit is the
A
kinetic energy
B
potential difference
C
electromotive force
D
electrical energy
correct option: b
Users' Answers & Comments34
Which of the following is an essential physical property of the wires used for making fuses?
A
low density
B
high thermal conductivity
C
low electrical resistivity
D
low melting point
correct option: d
Users' Answers & Comments35
Which of the following is most suitable for protecting the circuit of 2000W electric iron connected to a 250V mains?
A
13A
B
8A
C
5A
D
3A
36
Electrical power is transmitted at a high voltage rather than low voltage because the amount of energy loss is reduced due to
A
heat dissipation
B
production of eddy currents
C
excessive current discharge
D
excessive voltage distance
correct option: a
Users' Answers & Comments37
A lamp is rated 240V, 60W. The resistance of the filament is
A
960\(\Omega\)
B
16\(\Omega\)
C
15\(\Omega\)
D
4\(\Omega\)
correct option: a
P = \(\frac{V_2}{R}\) \(\Rightarrow\) R = \(\frac{V_2}{p}\)
= \(\frac{240\times 240}{60}\)
= 960\(\Omega\)
Users' Answers & Comments= \(\frac{240\times 240}{60}\)
= 960\(\Omega\)
38
A 0 - 10mA galvanometer with a coil resistance of 30\(\Omega\) can be converted to a 0 - 10A ammeter by using
A
0.03\(\Omega\) series resistor
B
0.03\(\Omega\) shunt resistor
C
9.99\(\Omega\) shunt resistor
D
9.99\(\Omega\) series resistor
correct option: b
Users' Answers & Comments39
The number of neutrons contained in the nucleus \(^{238}_{92}U\) is
A
92
B
146
C
238
D
330
40
What precaution should a manufacturer take to ensure that energy loss in a transformer is minimized?
A
the winding of the transformer should be made of high resistance wire
B
the core should be made of thin sheets of metal
C
no magnetic material should be used to make the core
D
the flux linking the primary with the secondary coils should be minimum
correct option: b
Users' Answers & Comments