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JAMB Physics Past Questions & Answers - Page 322

1,606.

An ebonite rod rubbed with fur attracts a glass rod rubbed with silk because

ebonite has a negative charge while glass has a positive charge

ebonite has a positive charge while glass has a negative charge

both have negative charges

both have positive charges

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

1,607.

The force of repulsion between two point positive charges 5 $\mu$ C and 8 $\mu$ C separated at a distance of 0.02 map art is. [ $\frac{1}{4{\pi}{\varepsilon}_o}$ = 9 x 10⁹Nm²C^-2]

1.8 x 10^-10N

9.0 x 10^-8N

9.0 x 10²N

4.5 x 10³N

View answer & explanation

Correct answer is C

F = $\frac{1}{4{\pi}{\varepsilon}_o}$ x $\frac {q_1q_2}{r^2}$

F = $\frac {5 {\times} 10 {\times} 8 {\times} 10}{0.002 {\times} 0.002}$ x 9 x 10

F = 900N

1,608.

Which of the following are true about the infra-red radiation?

i. it is invisible
ii. it is called heat ray
iii. its frequency is higher than that of blue light
iv. it travels as a transverse wave

i, ii, iii and iv

i, ii, iv only

i, iii, iv only

ii, iii, iv only

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

1,609.

A man wears convex lens glasses of focal length 30cm in order to correct his eye defect. instead of the optimum 25cm, his least distance of distinct vision is

14cm

28cm

75cm

150cm

View answer & explanation

Correct answer is A

F = $\frac{uv}{u - v}$

F = +ve

v = -ve

30 = $\frac {25 {\times} (-v)}{25 - (-v)}$
v = $\frac {25 {\times} (-v)}{25+v}$
v = 14cm

(Note that either negative or positive values go to show the positioning and hence, they are not a strong necessity in your final answer.)

1,610.

The displacement d produced in a glass block of thickness t and refractive index n when an object is viewed through it is

t – n

t (1 + 1/n)

t (1-1/n)

t (1/n - 1)

View answer & explanation

Correct answer is C

n = $\frac {\text{real depth}}{\text {apparent depth}{}}$

n = $\frac {t}{t-d}$

$\frac{t - d}{1}$ = $\frac{t}{n}$

-d = $\frac{t}{n}$ - t

d = - $\frac{t}{n}$ + t

d = t - $\frac{t}{n}$

d =t (1 - $\frac{1}{n}$ )