A certain manufacturer wishes to make an n-type semiconductor. Which materials would he select for doping?

• A) boron and antimony
• B) aluminium and antimony
• C) aluminium and indium
• D) arsenic and antimony

I. The frictional force is independent of the area of the surfaces in conduct II. The frictional force depends on the nature of the surfaces in contact III. The frictional force depends on the speed of sliding IV. The frictional force is directly proportional to the normal reaction.

Which combination of the above is true of sliding friction?

• A. I, III and IV
• B. I, II and IV
• C. I, II and III
• D. II, III and IV

A particle of charge q and mass m moving with a velocity v enters a uniform magnetic field of strength B in the direction of the field. The force on the particle is

• A. qvB
• B. mqvB
• C. qvB/m
• D. mvB/q

Gamma rays are produced when

• A. high velocity electrons are abruptly stopped in metals
• B. energy changes occur within the nucleus of atoms
• C. energy changes occur within the electronic structure of atoms
• D. electrons are deflected in very strong magnetic fields

List three observations in support of the de-Broglie's assumptions that moving particles behave like waves.

A student is at a height 4m above the ground during a thunderstorm. Give that the potential difference between the thundercloud and the ground is 107v, the electric field created by the storm is

• A. 2.0 × 10⁶ NC^-1
• B. 2. 5 × 10⁶ NC^-1
• C. 1.0 × 10⁷ NC ^-1
• D. 4.0 × 10⁷ NC ^-1

An object of mass 20kg is released from a height of 10m above the ground level. The kinetic energy of the object just before it hits the ground is

• A. 200J
• B. 4000J
• C. 2000J
• D. 500J

Two mirrors are inclined as shown in the diagram. A ray of light RO strikes the arrangement at O and emerges along PO. The emergent ray has been deviated through

• A. 240°
• B. 180°
• C. 120°
• D. 60°

The property of a fluid that is used to determine its suitability as a lubricant is its

• A. capillarity
• B. viscocity
• C. surface tension
• D. relative density

Which of the following is correct about an electric cell?

• A. Primary cell produces a large current for a long time
• B. Secondary cell has a very high internal resistance
• C. Primary cell has a very low internal resistance
• D. Secondary cell has a very low internal resistance