Question 76:

• JAMB 1979

Which of the following statements is correct? The magnetized state of an iron bar can be destroyed completely by

A. Heating the bar to a high temperature
B. Breaking the bar
C. Connecting opposite poles with a small piece of iron
D. Placing the bar inside a strong magnetic field
E. None of the above

Question 77:

• JAMB 1979

An electric cell has an internal resistance of 2 ohms. A current of 0.5A is found to flow when a resistor of 5 ohms resistance is connected across it. What is the electromotive force of the cell?

A. 5 volts
B. 3.5 volts
C. 2.5 volts
D. 1 volts
E. 10 volts

Question 78:

• JAMB 1979

Which of the following is the correct definition of 'half-life'?

A. The average life-time of a radioactive material
B. The time it takes a radioactive material to decay to half of its original quantity
C. Half the period a radioactive material decays completely
D. Half of the decay constant
E. The decay constant times life-time

Question 79:

• JAMB 1979

The bulb of a motorcycle head-lamp is marked 40W, 6V. The resistance of the filament when it is switched on is

A. \(\frac{6^2}{40^2}\)ohms
B. \(\frac{40}{6^2}\)ohms
C. \(\frac{40}{6}\)ohms
D. 6 x 40 ohms
E. \(\frac{6^2}{40}\)ohms

Question 80:

• JAMB 1979

In an electrolysis experiment, a cathode of mass 5g is found o weigh 5.01g after a current of 5A flows for 50 seconds. What is the electrochemical equivalent of the deposited substance?

A. 0.00004g/C
B. 0.00002g/C
C. 0.02500g/C
D. 0.05000g/C
E. 0.00001g/C