Question 551:

• JAMB 1989

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

Question 552:

• JAMB 1989

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

Question 553:

• JAMB 1989

Three resistors, with substances 250\(\Omega\), 500\(\Omega\) and 1k\(\Omega\) are connected in series. A 6V battery is connected to either end of the combination. Calculate the pot3ential difference between the end of the 250\(\Omega\) resistor.

A. 0.20V
B. 0.86V
C. 1.71V
D. 3.43V

Question 554:

• JAMB 1989

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

Question 555:

• JAMB 1989

An ammeter of resistance 1.0\(\Omega\) has a full-scale deflection of 50mA. Determine the resultant full-scale deflection of the meter when a shunt of 0.0111\(\Omega\) is connected across its terminals.

A. 400mA
B. 450mA
C. 500mA
D. 550mA