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Physics
WAEC / WASSCE 1991
Electrostatics & Capacitors
Diagram
Solution
Two capacitors C1 and C2 are connected as shown in the diagram. The capacitance C2 is twice C1 when the key is opened the energy stored up in C1 is W. If the key is later closed and the system is allowed to attain electrical equilibrium, the total energy stored in the system will be
Attached Figure / Diagram
A
\(\frac{1}{2}\)W
B
\(\frac{2}{3}\)W
C
W
D
2w
E
3W
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
E = \(\frac{1}{2} Cr^2 = \frac{1}{2}(C-1 + C_2)V^2 = (3C_1)V^2\)
= 3(\(\frac{1}{2}C_1v^2\)) = 3W
Source: Myschool Past Questions Archive (Record #33428)
Physics
WAEC / WASSCE 1991
Current Electricity & Electric Circuits
Diagram
In which of the points labelled A, B, C, D and E on the conductor shown would electric charge tend to concentrate most?
Attached Figure / Diagram
A
A
B
B
C
C
D
D
E
E
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #33431)
Physics
WAEC / WASSCE 1991
Current Electricity & Electric Circuits
Solution
Which of the following is stored by dry Leclanche cell?
A
chemical energy
B
nuclear energy
C
solar energy
D
heat energy
E
electrical energy
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
The energy stored in the dry Leclanche cell is the chemical energy. It converts the chemical energy to electrical energy.
Source: Myschool Past Questions Archive (Record #33432)
Physics
WAEC / WASSCE 1991
Current Electricity & Electric Circuits
Diagram
Solution
Using the data in the circuit illustrated above, calculate the value of R
Attached Figure / Diagram
A
0.02\(\Omega\)
B
0.05\(\Omega\)
C
5.00\(\Omega\)
D
20.00\(\Omega\)
E
50.00\(\Omega\)
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
R = \(\frac{V}{T} = \frac{2v}{40 \times 10^{-3}}\)
= 50.00\(\Omega\)
Source: Myschool Past Questions Archive (Record #33433)
Physics
WAEC / WASSCE 1991
Calorimetry, Latent Heat & Change of State
Solution
A 90W immersion heater is used to supply energy for 5 minutes. The energy supplied is used to completely melt 160g of a solid at its melting point. Calculate the specific latent heat of the solid.
A
2.81jg-1
B
6.25Jg-1
C
8.89Jg-1
D
168.75Jg-1
E
5333.33Jg-1
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
pt = ml 80
90 x 5 x 60 = 160 x L
L = \(\frac{27000}{160}\)
= 168.75Jg-1
= 168.75
Source: Myschool Past Questions Archive (Record #33434)
Physics
WAEC / WASSCE 1991
Current Electricity & Electric Circuits
Diagram
Solution
In the circuit above R is a resistor whose resistance increases with an increase in temperature. L1 and L2 are identical lamps. If the temperature of R increases
Attached Figure / Diagram
A
L1 becomes brighter and L2 becomes dimmer
B
L1 becomes brighter and L2 does not change
C
L2 becomes dimmer and L1 does not change
D
L1 becomes dimmer and L2 does not change
E
L1 and L2 becomes brighter
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
L2 is in series with the resistor while L1 is in parallel to the resistor, therefore both L1 and L2 will become brighter.
in series connection high resistance produces a brighter glow while in parallel connection lower resistance produces a brighter glow.
Source: Myschool Past Questions Archive (Record #33435)
Physics
WAEC / WASSCE 1991
Magnetism, Electromagnetism & AC Circuits
Solution
A house is supplied with a 240V a.c mains. To operate a door bell rated at 8v, a transformer is used if the number of turns in the primary coil of the transformer is 900. calculate the number of turns in the secondary coil of the transformer
A
30
B
240
C
248
D
450
E
1248
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
\(\frac{E_p}{E_s} = \frac{n_p}{n_s}\)
ns = 30
Source: Myschool Past Questions Archive (Record #33438)
Physics
WAEC / WASSCE 1991
Current Electricity & Electric Circuits
Diagram
The diagram above shows a current carrying wire between the poles of a magnet. In which direction would the wire tend to move?
Attached Figure / Diagram
A
into the paper
B
out of the paper
C
towargs the north pole of the magnet
D
towards the south pole of the magnet
E
towards the top of the pages
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #33440)
Physics
WAEC / WASSCE 1991
Gas Laws & Heat Transfer
When a metal surface is irradiated, photoelectrons may be ejected from the metal. The kinetic energy of the ejected electrons depends on the
A
sorce of the radiation
B
intensity of the radiation
C
detection device for the electrons
D
amplitude of the radiation
E
frequency of the radiation
medium Difficulty
Verified Correct Answer: Option E
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option E.
Source: Myschool Past Questions Archive (Record #33448)
Physics
WAEC / WASSCE 1991
Work, Energy, Power & Simple Machines
Solution
An electron charge 1.6 x 10-19C is accelerated in vacuum from rest at zero volt towards a plate at 40k V. Calculate the kinetic energy of the electron
A
4.0 x 10-26J
B
4.0 x 10-21J
C
6.4 x 10-20J
D
3.2 x 10-15J
E
2.5 x 10-20J
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
E = \(\frac{1}{2}QV = \frac{1}{2} \times 1.6 \times 10^{-19} \times 40000\)
= 3.2 x 10-15J
Source: Myschool Past Questions Archive (Record #33450)
Physics
WAEC / WASSCE 1991
Atomic, Quantum, Nuclear Physics & Electronics
Solution
The half-life of a radioactive substance is 2 seconds. Calculate the decay constant
A
0.035s-1
B
0.151s-1
C
0.347s-1
D
0.576s-1
E
1.386s-1
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
\(\lambda = \frac{0.693}{T_{\frac{1}{2}}} = \frac{0.693}{2}\)
= 0.347s-1
Source: Myschool Past Questions Archive (Record #33453)
Physics
WAEC / WASSCE 1991
Atomic, Quantum, Nuclear Physics & Electronics
Solution
The work function of a metal is 4.65ev and the metal is illuminated with a radiation of 6.86ev. What is the kinetic energy of the electrons ejected from the surface of the metal?
A
1.48ev
B
2.21ev
C
4.42ev
D
5.75ev
E
11.51ev
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
K.E = \(\frac{1}{2}\)mv2
E - W = 6.86 - 4.65
= 2.21ev
Source: Myschool Past Questions Archive (Record #33454)
Physics
WAEC / WASSCE 1991
Elasticity, Density, Pressure & Fluids
Which of the following has the highest surface tension?
A
cold water
B
soapy water
C
warm water
D
oily water
E
salty water
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #33458)
Physics
WAEC / WASSCE 1991
Atomic, Quantum, Nuclear Physics & Electronics
Solution
(a)(i) By means of a labelled diagram, describe the mode uf operation of a modern X-ray tube.
(ii) State the energy transformation which takes place during the operation.
(b) Explain the terms hardness and intensity as applied to X-rays
(c)(i) State three uses of X-rays
(ii) State one hazard of over-exposure to X-rays in a radiological laboratory, indicating two safety precautions.
A
cold water
B
soapy water
C
warm water
D
oily water
E
salty water
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
(a)(i)
Mode of Operation:
In the X-ray tube a Low voltage high p.d is applied between the hot cathode and the anode. Electrons are emitted from the cathode and are accelerated to an extremely high speed. They are suddenly decelerated when they strike the anode causing the emission of high - energy radiation of short wavelength - X-ray. In this process the anode becomes very hot, and requires cooling fins on the outside of the tube.
Energy Transformation: The electrons have kinetic energy which is partly changed to internal energy (potential) and finally changed to heat energy.
(b) Hardness: Refers to X-rays with high penetrating power, short wavelength but high frequency. They are produced by increasing the p.d. between the cathode and anode. Such X-rays are called hard X-rays. Less penetrating or lower frequency ones are called soft X-rays. They are produced at lower p.d.
Intensity: High intensity X-rays beam results from the increase of current through the filament which leads to increase in the number of electrons.
(c)(i) Uses of X-rays:
(1) Investigating the structure of crystals ; (2) X-ray examination of the body for broken bones; (3) As invincible bullets for the treatment of tumours ; (4) Examination of metals for defects and fractures.
(ii) They may cause damage to living tissue and to cells. Precaution to be taken includes lead screening and regular health checks.
Source: Official Exam / Past Question Archive
English Language
WAEC / WASSCE 1991
Antonyms (Opposite in Meaning)
Instruction. Choose the word opposite in meaning to the underlined word in the sentence.
The measures that were introduced to accelerate the process of national development have in actual fact ...it
A
accentuated
B
retarded
C
promoted
D
neutralized
E
revoked
medium Difficulty
Verified Correct Answer: Option B
Grammar & Contextual Explanation
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #23436)