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

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

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

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

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.