1994 - WAEC Physics Past Questions and Answers - page 3
21
A particle of charge q and mass m moving with a velocity v enters a uniform magnetic field of strength B in the direction of the field. The force on the particle is
A
qvB
B
mqvB
C
qvB/m
D
mvB/q
correct option: a
Users' Answers & Comments22
A lamp marked 100W, 250V is lit for 10 hours. If it operates normally and 1KWh of electrical energy costs 2k, what is the cost of lighting the lamp?
A
1k
B
2k
C
5k
D
10k
23
Which of the following is a stringed instrument?
A
Flute
B
Trumpet
C
Piano
D
Drum
correct option: c
Users' Answers & Comments24
A transformer with 5500 turns in its primary winding is used between a 240V a.c supply and 120V kettle. Calculate the number of turns in the secondary winding
A
11000
B
2750
C
460
D
550
correct option: b
\(\frac{E_s}{E_p} = \frac{N_s}{N_p} ; \frac{120}{240}= \frac{N_s}{5500} thus N_s\)=2750
Users' Answers & Comments25
Beta particles are
A
electrons
B
protons
C
neutrons
D
helium nuclei
correct option: a
Users' Answers & Comments26
Which of the following substances is not an insulator?
A
Aluminium
B
Glass
C
Plastic
D
Clay
correct option: a
Users' Answers & Comments27
When an atom loses or gains a charge, it becomes an
A
ion
B
an electron
C
a neutron
D
a proton
correct option: a
Users' Answers & Comments28
In 24 days a radioactive isotope decreases in mass from 64g to 2g. What is the half life of the radioactive material
A
0.75 days
B
2.58 days
C
4 days
D
4.80 days
correct option: d
64g → 32g → 16g → 8g → 4g → 2g
Half life time= 24/5 = 4.8 days
Users' Answers & CommentsHalf life time= 24/5 = 4.8 days
29
The nucleon number and the proton number of a neutral atom of an element are 238 and 92 respectively. What is the number of neutrons in the atom?
A
330
B
238
C
146
D
119
30
The wave function of a metal is 8.0 x \(10^{-19}\)J. Calculate the wavelength of its threshold frequency. (Speed of light in a vacuum = 3 x \(10^8ms^{-1}, Planck's constant = 6.6 \times 10^{-34}\)Js)
A
0.8 x \(10^{-7}\)m
B
1 x \(10^{-7}\)m
C
2.3 x \(10^{-7}\)m
D
3.8 x \(10^{-7}\)m
correct option: c
\(\theta = E - E_f = h_f = \frac{v}{\lambda} \Rightarrow = \lambda = \frac{h_v}{\theta}
\frac{6.6\times 10^{-34} \times 3 \times 10^{8}}{8.6 \times 10^{-19}} = 0.8 \times 10^{-7}\)m
Users' Answers & Comments\frac{6.6\times 10^{-34} \times 3 \times 10^{8}}{8.6 \times 10^{-19}} = 0.8 \times 10^{-7}\)m