WAEC GCE Physics Theory/Essay Questions and Answers 2017 | Check Past Questions Here
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WAEC GCE 2017 Physics OBJ & Theory/Essay QUESTION AND ANSWERS
The resources below on Physics have been provided by WAEC to assist you understand the required standards expected in Physics final Examination. Students performance in examination under review was done by the Chief examiner, this you will see while exploring links like General Comment, Performance, Weaknesses, Strength and Expected Answers to Questions.
Question 1
A stone is projected vertically upward with a speed of 30ms-1 from the top of a tower
of height 50m. Neglecting air resistance, determine the time of flight on reaching the
ground.[g = 10ms-2]
Comments
This question on projectile motion was very popular among the candidates and was fairly well attempted. However, some candidates did not understand the difference between projectile from a height and that from a level ground. Projectile is mostly considered as taking place along a parabolic trajectory and most candidates use the stereotype parabolic equation as against using the linear equations for vertical motion under gravity, few candidates that used the correct equations also substituted wrongly.
The expected answer is:
Time taken to reach maximum height
h = ut – ½ gt2
-50 = 30t – ½ x 10 x t2
5t2 – 30t – 50 = 0
t2 – 30 – 10 = 0
t = 6 ±
2
= 7.36 s/7.4 s
OR
V = u – gt
0 = 30 – 10t
t = 3s
Maximum height reached
V2 = u2 - 2gx
0 = 900 - 20x
x = 45m.
Time taken to reach the ground from maximum height
x = ut + ½ gt2
45 + 50 = 0 + ½ x 10t2
t = 19 = 4.4
Time of flight = 3 + 4.4 = 7.4s
Question 2
A body of mass 0.5 kg is thrown vertically upwards with a speed of 25ms-1. Calculate the
potential energy of the body at the maximum height reached.
Comment
This question tested candidates understanding on the concept of conservation of energy. Majority of the candidates were able to solve this problem. However, few candidates could not solve this question correctly because they lack the knowledge that at maximum height the potential energy P.E is equal to the kinetic energy K.E
The expected answer is:
At max. Ht, P.E = initial K.E
= ½ mu2
= ½ x 0.5 x (25)2
= 156.25 J
OR
V2 = u2 - 2gh
At maximum height, v = 0
O = 252 - 2 x 10h
h = 31.25m
P.E = mgh
= 0.5 x 10 x 31.25
= 156.25J
Question 2
List two:
(a) types of waves, other than light, that can be plane polarized;
(b) methods of polarizing an unpolarized light.
Comments
This question on light waves was popular among the candidates and was well attempted
The expected answers are:
(a) Waves other than light that can be plane polarized
Radio waves
X - rays
§ – rays
Ultraviolet rays
Infrared rays.
(b) Methods of polarizing an unpolarized light
- Reflection(from smooth surface)
- Double refraction(through crystals)
- Selective absorption(in certain crystals)
- Scattering (by small particles)
- Polaroid.
Question 3
(a) What is electrolysis?
(b) A current of 2A is passed through a copper voltameter for 5 minutes.
Determine the mass of the copper deposited.
[Electrochemical equivalent of copper = 3.27 x 10-7 kg C-1]
Comments
This was another popular question among the candidates and was fairly well attempted. Some candidates however, lost marks for using wrong terminologies. Examples instead of decomposition some candidates used dissociation or disassociation. Instead of electrolytes some candidates used substances.
The expected answers are:
(a) Electrolysis is the process by which a solution or a molten substance is broken down into its component parts by the passage of (a direct) electric current/electricity.
(b) Mass of copper deposited = zIt
= 3.27 x 10-7 x 2 x 5 x 60
= 1.962 x 10 -4 kg.
Question 5
State two:
(a) differences;
(b) similarities
between thermionic and photoelectric emission.
Comments
Candidates performance in this question was poor. Most of them could neither state the similarities nor the differences between photoeletronic emission and thermionic emission.
The expected answers are:
(a) Differences between thermionic and photoelectric emission
Thermionic emission
- Caused by heat/themalenergy
- Electrons are released at a particular temperature
- Time rate of emission of electrons increases with increase in temperature
Photoelectric emission
- Caused by lightelectromagnetic wave energy
- Electrons are released at threshold frequency
- Time rate of emission of electrons increases with/is proportional to increase in intensity
(b) Similarities between thermionic and photoelectric emission
- both are surface phenomena
- electrons are released in both cases
- ejected/emitted electrons have kinetic energy.
Question 6
The table shows the pointer reading of a spring balance when different weights are hung on it. Determine the value of F.
Weight/N 5 10 F
Pointer reading/cm 8 12 30
Comments
Candidates performance in this question was poor. Most of them could neither state the similarities nor the differences between photoeletronic emission and thermionic emission.
The expected answers are:
(a) Differences between thermionic and photoelectric emission
Thermionic emission
- Caused by heat/themalenergy
- Electrons are released at a particular term
- Many candidates attempted this question and majority of them faired very well in it.
The expected answer is:
F = ke
10 – 5 = k(12 – 8) ……..(A)
F – 10 = k(30 – 12) ……..(B)
Solving simultaneously equations (A) and (B)
F = 32 . 5N
Perature
Time rate of emission of electrons increases with increase in temperature
Photoelectric emission
- Caused by light electromagnetic wave energy
- Electrons are released at threshold frequency
- Time rate of emission of electrons increases with/is proportional to increase in intensity
(b) Similarities between thermionic and photoelectric emission
- both are surface phenomena
- electrons are released in both cases
- ejected/emitted electrons have kinetic energy.
Question 8
Using the kinetic theory, explain the rise of water in a glass capillary tube.
This question was fairly answered by most candidates. However, some of the candidates lost marks because they left out “molecules” where necessary in their statements.
Comments
The expected answer is: Glass and water are composed of different molecules. The force of attraction between the glass molecules and the water molecules is stronger than that among water molecules hence the rise of water in the tube.
Question 9
Explain briefly the principle of action of a discharge tube.
Comments
This question was poorly attempted by the few candidates that attempted it. Many of them described the discharge tube instead of explaining its working principle.
The expected answer is: The pressure of air/gas in the closed tube is reduced using a (vacuum) pump. A (very)high voltage is applied across the electrodes. The remaining air/gas at (very) low pressure conducts giving rise to a discharge (between the electrodes).
Question 10
State Heisenberg’s Uncertainty Principle
State one phenomenon that can only be explained in terms of the wave nature of light.
Comments
Most candidates were able to state the Heisenberg’s Uncertainty principle though some left out the key word “simultaneously” in their statement. Majority were also able to state the phenomenon that illustrate wave nature of light. Generally the question was well attempted.
The expected answers are:
a) It is impossible to determine with accuracy both the position and momentum of a particle simultaneously
OR
p x ≥ h/2π
Where all symbols are correctly specified i.e
h = plank’s constant ; p = uncertainty / error in momentum, x = uncertainty / error in position.
NOTE: Accept h, h or h in place of h 4 2
(b) One phenomenon correctly mentioned e.g. - diffraction and interference.