JAMB Physics Past Questions & Answers - Page 259

1,291.

A calibrated potentiometer is used to measure the e.m.f. of a cell because the

A.

internal resistance of a cell is small compared with that of the potentiometer

B.

potentiometer has a linear scale

C.

potentiometer takes no current from the cell

D.

resistance of the potentiometer is less than that of a voltmeter

Correct answer is C

No explanation has been provided for this answer.

1,293.

The resistance of a 5m uniform wire of cross-sectional area 0.2 x 10-6m2 is 0.425. What is the resistivity of the material of the wire?

A.

1.10 x 10-6\(\Omega\)m

B.

4.25 x 10-6\(\Omega\)m

C.

2.40 x 10-7\(\Omega\)m

D.

1.70 x 10-8\(\Omega\)m

Correct answer is D

Resistance = \(\frac{\text{ Resistivity x Area}}{Area}\)

= 0.425 x 0.2 x 10-6

= 1.7 x 10-8\(\Omega\)m

1,294.

A bar magnet is most effectively demagnetized by

A.

placing it in a N - 5 position and hitting it with a hammer

B.

subjecting it to an electric current from a battery

C.

bringing its north pole in contact with the north pole of a very strong magnet

D.

heating the magnet

Correct answer is A

No explanation has been provided for this answer.

1,295.

When a number of identical small magnets are arranged in a line, the strength of the resultant magnet

A.

is largest when they are arranged end to end

B.

is greatest when they are arrangedparallel with like poles adjacent to each other

C.

depends only on the number of magnets provided they arev parallel

D.

is greater when the magnets are arranged on a wooden surface than on a metaln surface

Correct answer is A

No explanation has been provided for this answer.