Physics Past Questions and Answers

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 27:

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 28:

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 29:

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 30:

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