2004 - WAEC Physics Past Questions and Answers - page 5
41
Calculate the energy stored in a 20\(\mu F\) capacitor. If the p.d between the plates is 40V
A
3.2 x 10-2J
B
1.6 x 10-2J
C
8.0 x 10-4J
D
4.0 x 10-4J
correct option: b
W = \(\frac{cv^2}{2} = \frac{20 \times 10^{-6} \times 40^{2}}{2}\)
= 1.6 x 10-2J
Users' Answers & Comments= 1.6 x 10-2J
42
Given that the gravitational constant is G. Newton's universal law of gravitation states that the force of attraction between two masses M1 and M2 separation by a distance r is
A
\(Gr^2 M_1M_2\)
B
\(Gr M_1M_2\)
C
\(\frac{GM_1 M_2}{r^2}\)
D
\(\frac{GM_1 M_2}{r}\)
correct option: c
Users' Answers & Comments43
A charge of 1.6 x 10-10C is placed in a uniform electric field of intensity 2.0 x 105 NC-1. calculate the magnitude of the electric force exerted on the change
A
3.2 x 105N
B
1.8 x 105N
C
3.2 x 10-5N
D
1.8 x 10-5N
44
Which of the following statements is not correct?
A
a magnetic field is a region in which a magnetic force will be detected
B
a magnetic line of force is a path along which a magnetic fields are scalar quantities it were free
C
magnetic fields are scalar quantities
D
neutral point are obtained where the earth's magnetic force is exactly equal and opposite to that due to a magnet
correct option: c
Users' Answers & Comments45
The main function of the mouth piece of a telephone is that it converts sound energy to
A
mechanical energy
B
electrical energy
C
chemical energy
D
thermal energy
correct option: b
Users' Answers & Comments46
An atom is normally electrically neutral because the
A
number of electrons is equal to the number of protons
B
number of electrons is equal to the number of neutrons
C
number of protons is equal to the number of neutrons
D
electrons of the atom are buried deeply in the nucleus
correct option: a
Users' Answers & Comments47
In which of the following devices is the principle of photoelectric effect not applicable?
A
close-circuit television camera
B
burglar alarm
C
solar cells
D
periscope
correct option: d
Users' Answers & Comments48
Which of the following statements about X-rays is not correct? They
A
are electromagnetic waves
B
can be used to study crystal lattice
C
can destroy living cells
D
are produced from the nucleus of an atom
correct option: d
Users' Answers & Comments49
A radioactive substance has a half-life of 3 days. If a mass of 1.55g of this substance is left after decaying for 15 days, determine the original value of the mass
A
49.6g
B
37.2g
C
24.8g
D
12.4g
correct option: a
\(1 \to \frac{1}{2} \to \frac{1}{4} \to \frac{1}{8} \to \frac{1}{16} \to \frac{1}{32}\)
\(\frac{1}{32} = 1.55g\)
1 = 1.55 x \(\frac{32}{1} = 49.6g\)
Users' Answers & Comments\(\frac{1}{32} = 1.55g\)
1 = 1.55 x \(\frac{32}{1} = 49.6g\)
50
Which of the following representations is correct for an atom X with 28 electrons and 30 neutrons?
A
\(^{30}_{28} X\)
B
\(^{28}_{30} X\)
C
\(^{58}_{30} X\)
D
\(^{58}_{28} X\)