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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
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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
\(\frac{GM_1 M_2}{r}\)
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43

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
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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
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45

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
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46

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
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47

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
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48

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
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49

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
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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
\(^{58}_{28} X\)
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