### Physics Past Questions

36
A semiconductor diode is used in rectifying alternating current into direct current mainly because it
• A. allows current to flow in either direction
• B. is non-linear
• C. offers a high input resistance
• D. allows current to flow only in one direction
JAMB 1999
37
if ∆x is the uncertainty in the measurement of the position of a particle along the x-axis and ∆Px is the uncertainty in the measurement of the linear momentum along the x-axis, then the uncertainty principle relation is given as
• A. ∆x ∆Px ≥ h
• B. ∆x ∆Px = 0
• C. ∆x ∆Px < h
• D. ∆x ∆Px = ∞
JAMB 1999
38
When a ship sails from salt water into fresh water, the fraction of its volume above the water surface will
• A. increase
• B. decrease
• C. remain the same
• D. increase then decrease
JAMB 2000
39
I. Its velocity is constant
II. No work is done on the body
III. It has constant acceleration directed away from the centre
IV. The centripetal force is directed towards the centre

Which combination of the above is true of a body moving with constant speed in a circular track?
• A. II and IV
• B. I and IV
• C. II and III
• D. I and III
JAMB 2000
40
The velocity ratio of a machine is 5 and its efficiency is 75%. What effort would be needed to lift a load of 150N with the machine?
• A. 20N
• B. 30N
• C. 40N
• D. 50N
JAMB 2000