JAMB Physics Past Questions & Answers - Page 312

1,556.

If a resistance is halved in value and the potential difference across it is tripled, then the ratio of the new current to the old one is

A.

1 : 6

B.

1 : 3

C.

2 : 1

D.

6 : 1

Correct answer is D

\(\frac{V_1}{V_2}\) = \(\frac{I_1R_1}{I_2R_2}\)

\(\frac{I_1}{I_2}\)V2 = 3V1 and R1 = 2R2

\(\frac{V_1}{3V_1}\) = \(\frac{I_1 \times\ 2R_2}{I_2\times R_2}\)

\(\frac{I_1}{I_2}\) = \(\frac{6}{1}\)

1,557.

At different locations on the earth's surface, the earth's magnetic field is

A.

the same in magnitude and direction

B.

the same in magnitude but different in direction

C.

different in both magnitude and direction

D.

different in magnitude but different in direction

Correct answer is A

No explanation has been provided for this answer.

1,558.

Two parallel plates at a distance of 8.0 x 10-3m apart are maintained at a p.d of 600 volts with the negative plate earthed. What is the electric field strength?

A.

4.8 Vm-1

B.

75.0Vm-1

C.

4800.0Vm-1

D.

75000.0Vm-1

Correct answer is D

E = \(\frac{voltage}{distance}\)

= \(\frac{600}{8 \times 10^2}\)

= 75000.0Vm-1

1,559.

Which of the following pairs of colours gives the widest separation in the spectrum of white light?

A.

Red and Violet

B.

Green and Yellow

C.

Red and Indigo

D.

Yellow and Violet

Correct answer is A

No explanation has been provided for this answer.

1,560.

A real object is placed at a distance ucm in front of a curved mirror of focal length fcm. If the image is upright and magnified, then the mirror is

A.

convex and u =2f

B.

concave and u = 2f

C.

convex and u = f

D.

concave and u = f

Correct answer is B

-The image formed by a concave lens is always virtual, erect and magnified.

-The image formed by a concave mirror can be real or virtual, enlarged or diminished, and erect or inverted, depending upon the distance of the object from the mirror