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Nabteb Physics Questions And Answers 2021
(a) i Define uniform acceleration
Answer: (a) i Uniform accelerating is when the velocity of a moving object increases by equal amounts
in equal intervals of time, no matter how small the time interval may be.
(a) (ii) Describe an experiment to determine acceleration due to gravity.
(a) Mention two factors that affect the melting point of a substance.
Answer 3 (a) The two factors are:
i. Prevailing pressure
ii. Purity of the substance
(b) Describe an experiment which could be performed in the laboratory to measure the melting
point of naphthalene. State one precaution which should be taken to achieve accurate result.
(a) State Newtons first and second laws of motion
(a) (i) Newtons 1st law: states that A body will continue in its state of rest or
uniform motion along a straight line unless it is acted upon by an (external)
(ii) Newtons 2nd Law: states that the time rate of change of momentum of a
body (mass x velocity) is proportional to the resultant force acting on it (and
it takes place) along the direction of action of this force.
Question (b) Explain the difference between force and impulse
Answer (b) The difference between force and impulse:
Force is that push or pull that will change or tend to change the state of rest or
uniform motion of a body while impulse is the product of the (average) force acting
on a body and the time duration which it acts.
OR Force – mass x acceleration while impulse = Force x time of action . OR Unit of force = Newton Unit of impulse = NS
Question C(i) A 100gm tennis ball was hit by a boy at a velocity 35m/s at a wall. It
stopped on the wall for 6.0×10-3 seconds before bouncing off at a
velocity of 31m/s. what was the average force the wall exerted on the ball?
Answer (c) i M = 100gm = 0.1kg
Initial Velocity Vi = 35m/s
Time = 6.0 x 10-3 Sec.
Final velocity V2 = -31m/s
(i) Explain what is meant by echo and discuss how it can be used to measure the
velocity of sound in air and the depth of the ocean.
(a) (i) An echo is the sound heard after the reflection of the sound waves from a plane
solid surface (hard surface).
How it can be used to measure the velocity of sound in air: Stand some distance
directly in front of a vertical wall and clap two hinged wooden board sharply
together and listen to hear the echo coming back from the wall. Clap repeatedly
and adjust the rate of clapping until each next clap coincides with the echo heard
from the previous clap. The time interval between successive claps is then equal to
the time taken for sound to travel twice the distance between the clapper and the
wall. After the correct rate of clapping has been achieved, use stop watch to
measure the time for about 20 clap intervals. Then the average time interval
between two successive claps can be got by dividing the total time interval by 20.
The lateral distance between the Clapper and the wall is measured.
Let this distance be D (metres) And let the average time interval for successive clap be t, then period of a clap and its echo equals
T = t Then velocity of sound V = 2D = 2nD n T t
b(i) Explain what is meant by Doppler’s effect.
Answer (b) (i) Doppler’s effect can be defined as the change in the frequency of sound heard by an
observer due to the relative motion of the source and the observer. An example is
the roar of the motor of a racing car as it approaches and recedes from an observer
at the race track. The motor seems to slow down as it passes the observer. Or also
the pitch of the whistle on a fast moving train sounds higher as the train approaches
the observer at a station than it does as the train passes by
Question b(ii) A truck moving at 120 km/hr sounded a horn of frequency 312Hz as it approaches a
bus stop. What is the frequency of the horn?
(a) State faraday’s law of electromagnetic induction
Answer (a) i. Faraday’s Law of electromagnetic induction states that:
i. Whenever there is a change in the magnetic flux linked by a circuit an e.m.f. is
induced in the circuit
ii. The magnitude of the induced e.m.f. or current is directly proportional to the time
rate of change of the magnetic flux or lines of force linking the circuit.
Question a (ii) State Lenz’s law of electromagnetic induction
Answer a(ii) Lenz’s law stats that: The induced current or (E.M.F.) always flows in
such a direction as to oppose the change producing it.
Question b(i) Name two electrical devices whose operation is based on the laws of
Answer (b) Two electrical devices whose operation is based on the laws of
electromagnetic induction are:
i. the transformer;
ii. the generator;
iii. the induction coil.
(Any two correct devices)
Question b (ii) Explain with clearly labeled diagram how a transformer works.
Question (a)i Explain using kinetic/molecular theory of matter why solid aluminium will change to
liquid at 6600C without change in its temperature.
Answer (a)i. Molecules of solid are in fixed position in the crystalline structure. They are held together
by intermolecular forces. This constraint makes them to vibrate about their mean
equilibrium position. Aluminum is a solid. As the temperature of the solid Aluminium
increases the atoms acquire greater kinetic energy and are able to vibrate farther apart from
their mean position, thus weakening the inter molecular forces binding them together. At a
certain maximum temperature (6600C)the molecules have maximum kinetic energy.
This maximum temperature is the melting point of the solid. Further heat supplied to the
substance does not increase the kinetic energy of molecules. Instead the heat energy is
used to break down the intermolecular forces binding the molecules together in the solid.
The molecules are then free and could slide over one another. The solid then melts at this
maximum temperature. Further heating only goes to break more bonds while the
temperature remains constant. The heat energy absorbed during this process is known as
the latent heat of fusion.
Question a(ii) Explain why evaporation causes cooling and give the factors which affect its rate.
Answer a(ii) The molecules of the liquid have an average velocity or average kinetic energy which
increases with temperature. Molecules near the surface which happen to move faster then
the average, escape from the attraction of their neighours and out of the liquid. Thus the
liquid loses its most energetic molecules while the less energetic ones are left behind. The
average K.E. of the remaining molecules is therefore reduced, which lowers the
temperature of the liquid hence evaporation causes cooling.
Factors affect evaporation are:
2. Exposed area of liquid surface
3. Prevailing wind
5. Prevailing atmospheric pressure
Question 4b(i) Describe an experiment to measure the specific heat capacity of a solid.
Answer 4b(i) The specific heat capacity of a solid in the form of a metal block can be determined by an
electrical method and method of mixture.
(1) By Electrical Method
Two holes are bored in as the block, after which the block is weighed. A thermometer and
an electrical hearter are inserted in each of the holes. A little oil in each hole keeps
establishing a good thermal contact with the block. The initial temperature of the block is
noted and the electrical heater is switched on and current allow flowing for sometime until
the temperature rises by about 150C. the exact time of flow of a known current is measured
Question (a) (i) Distinguish between intrinsic and extrinsic semi conductors and give TWO
examples of each.
Answer a (i) If conduction in a material results only from the electron movement from valence to
conduction band, it is called an intrinsic semiconductor. While semiconductor
materials containing different types of impurities are combine to produce the many
useful devices presently on the scene. The process of adding impurity to a
semiconductor is called doping, and the doped semiconductor is referred to as
extrinsic semi conduction.
E.g. (i) Intrinsic – Pure silicon, Germinium etc.
(ii) Extrinsic: – Gallium Arsenide, (gasa), Lead Tellurium
Question a(ii) What is a p-n Junction and how dos it work?
Answer a(ii) P-n junction consists of a p-type and n-type semiconductor in contact. When
forward bias (i.e. the P-semiconductor is connected to the positive terminal of a
battery and the n-Semiconductor is connected to the negative terminal of a battery,
it has a low resistance to current flow. When in reverse bias (i.e. the PSemiconductor is connected to the negative terminal of the battery and the nSemiconductor is connected to the positive terminal) it has a high resistance to current flow
Question b(i) Draw the I – V characteristics of a p-n Junction and explain how it can be used
Question: a. State Hook’s law
Answer: a. Hooks law states that provided the elastic limit of an elastic material is not exceeded, the
extension of the materials is directly proportional to the load or force applied. (F = K X).
F = KX (Provided the elastic limit is not exceeded)
Where F = Applied force or load
X = Extension
K = Proportionality constant or force constant
Question 1b. A helical spring is stretched by loading it gradually with increasing weights and the
corresponding extensions recorded until the elastic limit is reached. Draw a graph of load
against extension showing the following:
i. elastic limit
ii. yield point
iii. breaking point
Question a. Distinguish between electric conductors and insulators. Give FOUR examples
Answer: a. Electric conductors are materials that will allow easy movement of electrons through them.
While insulators are materials which do not allow easy movement of electrons through
them. A good conductor of electricity is a good conductor of heat.
Examples of conductor are: metal, damp air, salt solution, graphite, carbon black, the Earth
and the human body. (Any 4 examples)
Examples of insulator: polythene, bakelite ebonite, dry paper, dry hair, silk, oil, glass,
wood and surphur (Any 4 examples)
Question: b. What is a capacitor? Name THREE types of capacitors and THREE appliances that use
capacitor for operation.
Answer: b. A capacitor is a device for storing electric charges or for storing electricity
The three types of capacitors are (1) Variable air capacitor, (2) paper capacitor, (3)
Appliances that use capacitor are:
1. Radio tune circuit
2. Car ignition system
3. Induction coil to eliminate spark when a circuit containing inductance is opened
4. Fluorescent light tube starter
5. Starter of electric pumping machine
a(ii) Describe the application of this Principle in the working of car-braking
a(ii) WORKING OF A CAR BRAKING SYSTEM
When the brake pedal is pressed by the driver, the piston in the master cylinder is pushed. This
compresses the oil inside the tubes and the pressure is transmitted equally to the brake shoes by the caliper forcing the brake shoes and its pad against the brake drum to which the tyres are fixed. (The frictional force between the pad and the drum slows down the rotation of the wheels or can stop them entirely depending on how hard the driver pressed down on the pedals.) When the driver releases the brake pedal.
The pressure is released. A spring connected to the two arms of the brake shoes which had been stretched
by the force applied now returns, and pushed away from the drum giving clearance for the drum to rotate
freely once again.
Question b(i) With the aid of a diagram, describe the action of a siphon.
Question (a) Explain what is meant by a field
Answer (a): By a field, it is meant a region of space under the influence of some physical agency such
as gravitation, magnetism and electricity.
Question (b) Mention three types of fields known to you
Answer (b) Three types of fields are (1) Gravitational field (2) magnetic field (3) electrostatic field (4)
electromagnetic field. (Any 3 is correct).
Question (c) Distinguish between scalar fields and vector fields. Give two examples of each.
Answer (c) A Scalar field has only Magnitude but no direction (e.g. Temperature, Energy, density).
While a Vector field is that, that has both magnitude and direction (e.g. Gravitational field,
magnetic field and electric field).
Question d(i) What do you understand by the poles of a magnet? Using a magnet of known poles, how
can you differentiate between the 2 poles of another magnetic.
Answer d(ia) The pole of a magnet is that portion of the magnet where its magnetic attraction appears to
Answer d(ib) Suspend the magnet of known poles so that it can swing freely. Next bring one pole of the
other magnet near this. If they repel each other then they have similar poles while if they attract they are
of opposite sign.
Question d(ii) The Lines of a magnetic field do not cross, why?
Answer d(ii) The line of force of a magnetic field do not cross because the line of force is the line along
which a free N pole would tend to move if placed in the field or it is a line such that a tangent to it at any
Question b(i) How has electronic devices improved the quality of life of Doctors.
Answer b (i) Doctors: Electronic devices has helped them in making proper diagnosis of their
patients & much faster. (2) it has helped in carrying out delicate operations with great
efficiency. (3) it has helped the control and monitoring of recuperating patients particularly
those with heart or kidney problems.
Question 5b(ii) How has electronic devices improved the quality of life of the disabled.
Answer 5b(ii) Disabled: Provided them with:
a. Hearing aid.
b. Motorized wheelchairs.
c. Electronically controlled artificial lambs.
d. Electronically controlled cars.
Question 5b(iii) How has electronic devices improved the quality of life of Road traffic controllers
Answer 5b(iii) Road traffic controllers: Helped in
a. Controlling traffic flow at junctions and cross-roads by the operation of traffic lights.
b. Monitoring the number of vehicles plying a particular road.