2014 - WAEC Physics Past Questions and Answers - page 5
41
In the circuit diagram above, E is a battery of negligible internal resistance. If its emf is 9.0V. Calculate the current in the circuit ``
A
1.8A
B
1.0A
C
0.8A
D
0.3A
correct option: b
\(\frac{1}{r} = \frac{1}{r_1} + \frac{1}{r_2}\)
= \(\frac{1}{5} + \frac{1}{20}\)
= \(\frac{4 + 1}{20} = \frac{5}{20}\)
r = \(\frac{20}{5}\)
= 4\(\Omega\)
R = R1 + R2
= 5 + 4
= 9\(\Omega\)
but V = IR
I = \(\frac{V}{R} = \frac{9}{9}\)
= 1A
Users' Answers & Comments= \(\frac{1}{5} + \frac{1}{20}\)
= \(\frac{4 + 1}{20} = \frac{5}{20}\)
r = \(\frac{20}{5}\)
= 4\(\Omega\)
R = R1 + R2
= 5 + 4
= 9\(\Omega\)
but V = IR
I = \(\frac{V}{R} = \frac{9}{9}\)
= 1A
42
A wire of length 100 cm has a resistance of 10\(\Omega\). If its cross-sectional area is 0.005cm2, determine its resistivity
A
0.0005\(\Omega\)cm
B
0.0015\(\Omega\)cm
C
0.0016\(\Omega\)cm
D
0.0700\(\Omega\)cm
correct option: a
e = \(\frac{RA}{L} = \frac{10 \times 0.005}{100} = 0.0005\)
Users' Answers & Comments43
A transformer has 400 turns of wire in the primary coil and 40 turns in the secondary col. If the input voltage is 150 volts. Calculate the magnitude of the output voltage
A
150V
B
55V
C
36V
D
15V
correct option: d
\(\frac{ES}{EP} = \frac{Ns}{Np} = \frac{Es}{150} = \frac{40}{400}\)
Es = \(\frac{150 \times 40}{400}\)
= 15V
Users' Answers & CommentsEs = \(\frac{150 \times 40}{400}\)
= 15V
44
The circuit above illustrates a standard resistor R, voltage source E and a lamp L connected in series. If the temperature of R is increased, the brightness of the lamp will
A
increase sharply
B
decrease slightly
C
remains the same
D
increase gradually
correct option: b
Users' Answers & Comments45
The energy required to separate the nucleus in an atom completely is known as
A
mass defect of the atom
B
electron binding energy
C
excitation energy
D
nuclear bnding energy
correct option: d
Users' Answers & Comments46
Which of the following statements is the major advantage of nuclear fusion over nuclear fission?
A
nuclear fusion releases more energy
B
more neutrons are released in fusion than in fission
C
fussion does not release as much dangerous radiation as fission
D
fusion reactions occur more readily than fission
correct option: c
Users' Answers & Comments47
An aluminum foil is placed across a beam of radiation from a radioactive source. Which of the following types of radiation will be stopped by it?
A
alpha and beta particles
B
alpha and gamma particles
C
beta and gamma particles
D
gamma particles only
correct option: a
Users' Answers & Comments48
An element of nucleon number P and atomic number Q emits an alpha particle from its nucleus. The resultant numbers of the new element formed are respectively
A
P - 4 and Q + 2
B
P - 4 and Q - 2
C
P + 2 and Q + 2
D
P + 2 and Q - 2
correct option: b
Users' Answers & Comments