2005 - JAMB Physics Past Questions and Answers - page 2
11
When impurities are added to semi-conductors, the conductivity of the semi-conductor
A
increases then decreases
B
increases
C
decreases
D
remains constant
correct option: b
When impurities are added to semi conductor , the semi conductor is said to be doped, and increases the conductivity of the semi-conductor.
Users' Answers & Comments12
A silicon material is dopped with an element of a certain group and an n-type semi-conductor is formed. the most likely group of the element is
A
V
B
III
C
I
D
II
correct option: a
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)
Users' Answers & Comments13
The charge carriers in gasses are
A
ions only
B
electrons and ions
C
electrons and holes
D
electrons only
14
the ray which causes gas molecules to glow is known as
A
cathode ray
B
anode ray
C
molecular ray
D
gamma ray
correct option: a
The ray which causes gas molecules to fluoresce or glow is the cathode rays
Users' Answers & Comments15
the ray which causes gas molecules to glow is known as
A
cathode ray
B
anode ray
C
molecular ray
D
gamma ray
correct option: a
The ray which causes gas molecules to fluoresce or glow is the cathode rays
Users' Answers & Comments16
A transformer is rated 240v. If the primary coil is 4000 turns and the secondary voltage 12v, determine the number of turns in the secondary coil.
A
200
B
100
C
250
D
150
correct option: a
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= Ns/4000
Ns =(12x4000)/240
=200
Users' Answers & Commentswhere 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= Ns/4000
Ns =(12x4000)/240
=200
17
The current in a reverse-biased junction is due to?
A
minority carriers
B
electrons
C
majority carriers
D
holes
correct option: a
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.
Users' Answers & Comments18
which of the following materials is a conductor?
A
Glass
B
Wax
C
Sodium
D
Plastic
correct option: c
Users' Answers & Comments19
When the temperature difference between the wet and dry bulbs of a hygrometer is high, this indicates that
A
it is about to rain
B
the relative humidity is high
C
there is plenty of sunshine
D
the relative humidity is low
correct option: d
Users' Answers & Comments20
A 3m3 volume of liquid W of density 200kgm3 is mixed with another liquid L of volume 7m3 and density 150kgm-3. the density of mixture is?
A
165kgm-3
B
100kgm-3
C
265kgm-3
D
350kgm-3
correct option: a
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
Users' Answers & Commentssimilarly, 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