2009 - WAEC Physics Past Questions and Answers - page 5

41
An inductor of inductance 1.0H is connected in series with a capacitor of capacitance 2.0μF in an a.c. circuit. to resonate
A
112.5Hz
B
225.0Hz
C
323.5Hz
D
707.1Hz
correct option: a

fo = (\frac{1}{2 \pi \sqrt{LC}} = \frac{1}{2 \times 3.14 \sqrt{1 \times 2 \times 10^{-6}}})

= 112.5Hz

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42
An ammeter connected to an a.c circuit records 5.5. The peak current in the circuit is
A
7.8A
B
7.1A
C
3.8A
D
3.5A
correct option: a

(I_o = I_{rms} \times \sqrt{2} = 5.5 \times 1.41 = 7.8A)

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43
Two isotopes of uranium are designed as 238U and 235U. The numbers 238 and 235 represent their
A
atomic numbers
B
nucleon numbers
C
proton numbers
D
neutron numbers
correct option: b

neutrons + protons = the nucleus or mass numbers.

U-238 has mass number(proton 92 + neutron 146=238)
U-235 has mass number (proton 92 + neutron 143 =235)

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44
The main difference between between x-rays and γrays lies in their
A
ionizing ability
B
absorption rate
C
mode of production
D
mode of propagation
correct option: d
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45
An electron of mass 9.1 x 10-31 kg moves with a speed of 107ms-1. Calculate the wavelength of the associates wave[h = 6.6 x 10-34Js]
A
9.0 x 10-24m
B
4.55 x 10-17m
C
7.25 x 10-11m
D
6.20 x 10-8m
correct option: c

(\lambda = \frac{hc}{\frac{1}{2}mv^2})

= (\frac{6.6 x 10^{-34} \times 3 \times 10^8}{0.5 \times 9.1 \times 10^{-3} (10^7)^2})

= 7.25 x 10-11m

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