WAEC 2019 GCE Physics Questions and Answers – OBJ and Theory Answers.
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WAEC GCE Physics Questions 2019
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Verified Physics obj
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1a ” Cathode rays” are simply beams of
electrons. The name exists because cathode
ray devices predate the discovery of the
electron. The sharp shadows produced by
Crookes tubes meant that something was
travelling in a straight line from the cathode
down the tube, so they were named cathode
rays .
1b – They are produced by the negative
electrode, or cathode, in an evacuated tube,
and travel towards the anode.
– They travel in straight lines and cast sharp
shadows.
2)-Concentration of electrolyte
-Nature of electrode
-Positions of ions in the electrochemical series
3a In physics, a standing wave – also known
as a
stationary wave – is a wave in a medium in
which each point on the axis of the wave has an
associated constant amplitude. The locations
at which the amplitude is minimum are called
nodes, and the locations where the amplitude is
maximum are called antinodes
4a
-They are used in the fields of communications,
4b
-warfare
-in exploring space
5)-traveling wave tubes
-Hall Effect sensors
-high temperature-resistant permanent magnets
-thin-film coating equipment
-flywheel storage systems.
Question 5
At atmospheric pressure, air and other gases
are poor conductors (Insulators) of electricity.
Because, they don’t have any free electrons to
carry current. But, once the free electrons are
produced in gas byionization (they become
plasmas), electric discharge occurs.
This could be done in many ways such as by
applying a large potential difference across a
gas column at very low pressure, or by allowing
high frequency EM-waves such as the X-Rays
through the gas. This question is not proper to
ask. Indeed, gases become plasmas once
they’re ionized!
All dielectrics have a certain value ofbreakdown
potential. In most of them like air, ceramics,
etc. (including semiconductors like Silicon),
this potential provides sufficient energy to
ionize a few atoms. The free electrons formed
as a result of this ionization are energized
enough to bump the neighborhood atoms,
break some covalent bonds and produce more
free electrons.
7)The effect of Doping a Semiconductors. The addition
of a small percentage of foreign atoms in the regular
crystal lattice of silicon or germanium produces dramatic
changes in their electrical properties, producing n-type and
p-type semiconductors. Pentavalent impurities.
9 )Boyle’s law state that a law stating that the pressure of a
given mass
of an ideal gas is inversely proportional to its
volume at a constant temperature.
9 bi) Renewable energy is energy generated from
natural resources—such as sunlight, wind, rain,
tides and geothermal.They are energy sources that can be
replaced as they are used.They are continually replenished
9bii) rain
wind
Sunlight
Geothermal
10) states three different between sound and light waves
*Sound Waves*
1. Require a medium.
2. Travel with a speed of 332 m/s at 0 C.
3. Are longitudinal waves consisting of compressions and
rarefactions.
4. Are of different frequencies, giving notes of different
pitches.
5. Do not travel far as their energy is dissipated easily.
====================
*Light Waves*
1. Do not require a medium
2. Travel with a speed of 3 *10 8 m/s.
3. Are electromagnetic waves consisting of varying electric
and magnetic fields.
4. Are of different frequencies, resulting in different colors.
5. Can travel through a much greater distance.
(10a)
-Sound wave is mechanical wave while light wave is electromagnetic
-Sound wave is longitudinal wave while light wave is transverse wave
-Sound wave cannot be plane polarized while light wave can be plane polarized
(10bi)
DRAW THE DIAGRAM
(10bii)
Nature=>It is a real image and inverted
Position=>It is at 2f on the other side
Size=>It has the same size of the object
(10c)
Because the light ray travel on a straight line ie rectilinear propagation of light rays
(10d)
u=36m=3600cm
hi=2.5cm
v=0.30cm
(i)m=v/u
m=0.3/3600
m=0.000083
(ii)m=hi/ho
ho=hi/m
ho=2.5/0.000083
ho=30120cm
ho=301.2m
(iii)
1/f=1/u+1/v
1/f=1/3600+1/0.3
1/f=0.00028+3.33333
1/f=3.33361
f=0.3cm
=====================
(11a) principle of conservation of linear Momentum
states that in any system of colliding objects the total
momentum is always conserved provided that there is net
external force acting on the system.
(11bi)
Impulse IA = change in momentum of A
= final momentum of A
– initial momentum of A
MAVA – MAVA
Impulse IB = change in momentum of B
= MBVB – (MBUB)
= MBUB
11b) Farad is the standard unit of capacitance in the
International System of Units (SI), formally defined to be
the capacitance of a capacitor between the plates of which
there appears a potential difference of one volt when it is
charged by a quantity of electricity equal to one coulomb.
Symbol: F. Origin of farad Expand.
12a . decay constant is define as the instantaneous rate of
decay per unit atom of a substance.
12bi)The moderator is a material which slows down the
speed
of the neutrons . The moderator is
usually made from water but some reactors use graphite .
(12ai) Decay constant is defined as the instantaneous
rate of decay per unit atom of a substance.
(12aii)
Halflife ,T=0.693/decay contant. Hence, decay
constant,llamda =0.693/T ; =0.693/3days; =0.182day-1 i.e
per day.
(12bi) the moderator of a nuclear fission reactor is made
up of graphite. Its function is that slow down the
movement of a neutron,so that the chain reaction will not
dry out.
(12bii) the control rods is made of Boron steel.its function
is to ensure movement of the floor,so that it can shut off
the reactor automatically in case of electrical failure
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