JAMB Physics Past Questions & Answers - Page 162

806.

A sonometer wire under a tension of N10N, produces a frequency of 250Hz when plucked. Keeping the length of the wire constant, the tension is adjusted to produce a new frequency of 350Hz. Calculate the new tension

A.

39.2N

B.

19.6N

C.

14.2N

D.

7.4N

E.

5.1N

Correct answer is B

f \(\alpha\) \(\sqrt{T}\)

\(\frac{f_1}{f_2} = \sqrt{\frac{T_1}{T_2}}\)

\(\frac{250}{350} = \sqrt{\frac{10}{T_2}}\)

\(\frac{5}{7} = \sqrt{\frac{10}{T_2}}\)

\(\frac{25}{49} = \frac{10}{T_2}\)

T2 = \(\frac{49 \times 10}{25} = 19.6\)

807.

What is the image distance of an object placed at a distance of 2f from a converging lens of focal length f?

A.

f/4

B.

f/2

C.

f

D.

2f

E.

4f

Correct answer is D

No explanation has been provided for this answer.

809.

How much heat is emitted when a body of mass 200g cools from 37oC to 31oC? (specific heat capacity of the body = 0.4Jg-1K-1,)

A.

4800J

B.

1200J

C.

480J

D.

202J

E.

80J

Correct answer is C

H = mC\(\theta\) = 200 x 0.4 x 6

= 480J

810.

A piece of brass of mass 170kg has its temperature raised from 0oC to 30oC. Calculate its increase in volume, given the density of brass at 0oC as 8.5 x 103kgm3 and its cubic expansivity as 5.7 x 10-1k1

A.

3.4 x 10-5m3

B.

4.3 x 10-5m3

C.

3.4 x 10-5m3

D.

3.4 x 10-3m3

E.

3.4 x 10-2m3

Correct answer is C

V = \(\frac{m}{p}= \frac{170}{8.5 x 10^{-3}}\) = 0.02

= \(\Delta\)\(\frac{\delta V}{V \delta T}\)

\(\delta V\) = \(\Delta\) x V x \(\delta\)T

= 5.7 x 10-5 x 0,02 x 30

= 0 3.42 x 10-5