2005 - JAMB Physics Past Questions and Answers - page 2

When impurities are added to semi conductor , the semi conductor is said to be doped, and increases the conductivity of the semi-conductor.

Silicon is a tetra valent (4 valent) element, and in order to produce an n type semi-conductor, it has to be dropped with a penta valent (5valent)element, that, that is element in group five (v)

The charges carriers in gasses are the ions

The ray which causes gas molecules to fluoresce or glow is the cathode rays

The ray which causes gas molecules to fluoresce or glow is the cathode rays

in a transformer, E _S/E _P = N _s/N _p
where E _s=e.m.f(voltage)of the secondary
E _p=e.m.f(voltage)of the primary
N _s=no.of turns in the secondary
N _p= no. of turns in the primary.
since E _s= V _s; and E _p= V _p.
V _s/ V _p= N _s/N _p
∴12/240= N_s/4000
N_s =(12x4000)/240
=200

the current in reverse biased junction diode is due to minority carriers, that is, the negative charges in the p-semi-conductor, and the positive charges in the n-semi-conductor.

For liquid W, its mass = vol. x density = 3 x 200 =600kg.
similarly, for liquid L, its mass = 7 x 150 = 1050kg
∴ Total mass of mixture = 600kg + 1050kg =1650kg.
similarly total vol.of the mixture = 3m³ + 7m³ =10m³.
∴ density of the mixture = (Total Mass)/Total Mixture = (1650kg)/10m³
=165kgm^-3