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JAMB Physics Past Questions & Answers - Page 64

316.

A resistor connected to a 12V battery draws a current of 2A. The energy dispatched in the resistor in 5 minutes is ___.

A.

3,600J

B.

6,000J

C.

7,200J

D.

14,400J

View answer & explanation

Correct answer is C

Power drawn by the resistor = IV = (2)(3) = 24W = 24J/s

Energy dissipated = power × time = (24)(5)(60) = 7200J

317.

When a known standard resistor of 2.0 is connected to the 0.0cm end of a metre bridge, the balance point is found to be at 55.0cm

A.

1.10Ω

B.

1.64Ω

C.

2.44Ω

D.

27.50Ω

View answer & explanation

Correct answer is C

$\frac{R_1}{R_2}$ = $\frac{L_1}{(100 − L_1)}$

$\frac{R_1}{2}$ = $\frac{55}{45}$

R $_1$ = 2 × $\frac{55}{45}$
= 2.44Ω

318.

A lens of focal length 15cm forms an erect image which is three times the size of the object. The distance between the object and the image is ___

A.

10cm

B.

20cm

C.

30cm

D.

40cm

View answer & explanation

Correct answer is D

F= 15cm

M = 3

M = $\frac{v}{u}$

V =3u

$\frac{1}{f}$ = $\frac{1}{u}$ + $\frac{1}{v}$

$\frac{1}{15}$ = $\frac{1}{u}$ - $\frac{1}{3u}$

$\frac{1}{15}$ = $\frac{2}{3u}$

U =10cm

D = u + v

= 10 +30 = 40cm

319.

The image of an object is located 6cm behind a convex mirror. If it's magnification is 0.6, calculate the focal length of the mirror

A.

3.75cm

B.

6.70cm

C.

10.00cm

D.

-15.00cm

View answer & explanation

Correct answer is D

V = -6cm

M = 0.6cm

Recall m = $\frac{V}{U}$

U = $\frac{V}{M}$

U = $\frac{6}{0.6}$

U = 10

$\frac{1}{U}$ + $\frac{1}{V}$ = $\frac{1}{F}$

$\frac{1}{10}$ + $\frac{1}{-6}$ = $\frac{1}{F}$

$\frac{-4}{60}$ = $\frac{1}{F}$

F = $\frac{60}{-4}$

= -15cm

320.

If the focal length of a camera is 20cm, the distance from the film at which the lens must be set to produce a sharp image of 100cm away is

A.

17cm

B.

20cm

C.

25cm

D.

100cm

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

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