Common Questions Ask in Post UTME Physics Exams Day6

Common Questions Ask in Post UTME Physics Exams Day6

Physics

Chima Sunday (Tutor)
22-06-2016 15:19:00 +0000

Try your best to solve these questions. Show working on paper when necessary and include a picture of your hand written Solution in your response. Wish you the best!

1. A diverging lens of focal length 20cm forms an image half of the size of the object. What is the object distance.
A. 20cm
B. 100cm
C. 60cm
D. 8.71
(oau)

Updated Solution
For a diverging lens, f = -ve, and image is virtual
f = -20, magnification m = v/u = 1/2
thus v = -u/2 (virtual image)
from mirrors formular, 1/f = 1/u + 1/v = 1/u + 1/(-u/2) = 1/u - 2/u
1/f = 1/u - 2/u = -1/u
1/(-20) = -1/u
by subject formular, u = -1 × -20 = 20cm
Answer is Option A

2. An electric heater rated 1000W evapourates 100kg of water in 60sec. What is the specific latent heat of vapourization of water in j/kg.
A. 100
B. 200
C. 600
D. 300
(abu)

Updated Solution
P = W/t; W = Pt
heat gain = work done by the heater
So Wt = mL
by subject formular
L = Wt/m = (1000 × 60)/100 = 600J/kg
Answer is Option C

3. Which of the following is not true about semi-conductors
A. Moving holes are equivalent to moving positive charges
B. There are two kind of charge carriers, a free electron and hole
C. The escape of a valence electron from atom produces electron-hole pair of charge carriers
D. Increase in temperature increase in electrical resistance
(uniben)

Updated Solution
Semi-conductors have negative temperature co-efficient, thus its electrical resistance decrease with an increase in temperature
Answer is Option D

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