2012 - WAEC Physics Past Questions and Answers - page 4
31
Which of the following sets of coloured light is/are secondary colours i. Red, Blue and green ii. Blue, cyan and magneta iii. Green, Magenta and yellow, IV Yellow, Cyan and Magenta
A
i and ii only
B
ii and iii only
C
iv only
D
i, ii and iv only
correct option: c
Users' Answers & Comments32
When two like charges are brought together, the potential energy of the system formed will
A
increase because work is done against the field
B
increase because work is done by the field
C
decrease because work is done by the field
D
decrease because work is done against the field
correct option: d
Users' Answers & Comments33
Two capacitors, each of capacitance 2\(\mu\)F are connected in parallel. If the p.d across them is 120V, calculate the charge on each capacitor
A
6.0 x 10-5C
B
1.2 x 10-4C
C
2.4 x 10-4C
D
4.8 x 10-4C
correct option: c
C = \(C_1 + C_2 = 2 + 2 = 4 \mu F\)
but Q = CV
= 4 x 10\(^{-6}\) x 120
= 4.8 x 10\(^{-4}\)
\(\therefore\) Each of the capacitor has a charge of \(\frac{4.8 \times 10^{-4}}{2}\)
= 2.4 x 10\(^{-4}\) C
34
Which of the following properties is an advantage of lead-acid accumulator over an alkaline accumulator?
A
possesses low internal resistance
B
can be recharges
C
has shorter life span
D
possesses high e.m.f
correct option: d
Users' Answers & Comments35
Six dry cells each of e.m.f. 2.0 and internal resistance of 1.0\(\Omega\) are connected in parallel across a load of 3.0\(\Omega\). Calculate the effective current in the circuit
A
0.63A
B
0.50A
C
0.31A
D
.22A
correct option: a
I = \(\frac{f}{n} = \frac{1}{6 - 2}\)
I = \(\frac{v}{R + r} = \frac{2}{3} + \frac{1}{6} = 0.63\)
Users' Answers & CommentsI = \(\frac{v}{R + r} = \frac{2}{3} + \frac{1}{6} = 0.63\)
36
Two similar cells are used to light two similar lamps as illustrated in the diagrams above. In which of the circuit diagrams are the lamps brightest?
A
P
B
Q
C
R
D
S
correct option: a
Users' Answers & Comments37
A 120\(\Omega\) resistor dissipates 8 kJ of heat in 20s. Calculate the current through the resistor
A
5.8A
B
6.9A
C
30.0A
D
33.3A
correct option: a
Q = I2Rt
I = \(\sqrt{\frac{Q}{Rt}}\)
= \(\sqrt{\frac{8000}{12 \times 20}}\)
= 5.8
Users' Answers & CommentsI = \(\sqrt{\frac{Q}{Rt}}\)
= \(\sqrt{\frac{8000}{12 \times 20}}\)
= 5.8
38
The magnetic relay is a device used for
A
timing in sports
B
storing magnetic field
C
readin the magnitude of magnetic flux
D
controlling another circuit carrying larger current
correct option: d
Users' Answers & Comments39
the core of a transformer is usually laminated in order to
A
reduce magnetic leakage
B
reduce eddy current
C
prevent vibration of the transformer
D
make magnetic reversal in the core much easier
correct option: b
Users' Answers & Comments40
Which of the following modes is the most economical method of transmitting electrical power over long distances?
A
alternating current at low voltage and high current
B
alternating current at high voltage and high current
C
alternating current at high voltage and low current
D
direct current at low voltage and high current
correct option: c
Users' Answers & Comments