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Physics
WAEC / WASSCE 1992
Lenses & Optical Instruments
Diagram
In an experiment to measure1 the focal length f of a converging lens object distances u and corresponding image distance were measured and 1/u plotted against 1/v to obtain the graph illustrated. How would f be determined from this graph?
Attached Figure / Diagram
A
f= the slope of the graph
B
f= the intercept on the 1/u axis
C
f =the intercept on the 1/v axis
D
f = reciprocal of the slope
E
f = reciprocal of the intercept on either axes
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 #24266)
Physics
WAEC / WASSCE 1992
Lenses & Optical Instruments
Solution
The image of a pin formed by a diverging lens of focal length 10cm is 5cm from the lens. Calculate the distance of the pin from the lens
A
-3.3cm
B
3.3cm
C
10.0cm
D
15.0cm
E
20.0cm
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
Using the lens formula:
Using the lenses formula and applying the real-is-positive convention
\(\frac{1}{v}\) + \(\frac{1}{u}\) = \(\frac{1}{f}\)
f = -10cm for diverging lens, v = 5cm real image
\(\frac{1}{u}\) = \(\frac{1}{f}\) - \(\frac{1}{v}\)
\(\frac{1}{u}\) = \(\frac{1}{-10}\) - \(\frac{1}{5}\)
\(\frac{1}{u}\) = \(\frac{-1 - 2}{10}\) = \(\frac{-3}{10}\)
U = \(\frac{10}{-3}\) = - 3.33cm
The negative sign indicates that the object is on the same side as the incoming light.
Source: Myschool Past Questions Archive (Record #24267)
Physics
WAEC / WASSCE 1992
Lenses & Optical Instruments
As an object is moved close to the focus of a converging lens from infinity its image I. moves closer to the lens II. moves away from the lens. III. Remains the same size. IV becomes smaller. Which of the statements above is/are correct?
A
III and IV only
B
I and III only
C
IV only
D
III only
E
II only
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 #24268)
Physics
WAEC / WASSCE 1992
Lenses & Optical Instruments
Solution
A real image of an object fom1ed by a converging lens of focal length 15cm is three times the size of the object. What is the distance of the object from the lens?
A
30cm
B
25cm
C
20cm
D
15cm
E
10cm
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
1/u + 1/3u = 1/15; u = 20cm
Source: Myschool Past Questions Archive (Record #24269)
Physics
WAEC / WASSCE 1992
Reflection, Refraction & Dispersion of Light
Diagram
Solution
The eye defect illustrated in the diagram above can be corrected by a
Attached Figure / Diagram
A
convex mirror
B
concave mirror
C
diverging lens
D
converging lens
E
piano-converging lens
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
Short sight can be corrected by placing a suitable CONCAVE(diverging) lens in front of the eye.
Source: Myschool Past Questions Archive (Record #24270)
Physics
WAEC / WASSCE 1992
Current Electricity & Electric Circuits
In a domestic circuit, electrical appliances and lamps are arranged in parallel across the mains so as to enable the
A
same current to flow through the electrical appliances and the lamps
B
maximum energy to be consumed at least cost
C
same fuse to be used for the electrical appliances and the lamps
D
voltage across the appliances not to be affected when the lamps are switched on and off
E
heat losses to be minimized
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #24286)
Physics
WAEC / WASSCE 1992
Current Electricity & Electric Circuits
Solution
Calculate the time in which 4.8 kJ of energy would be expended when an electric heater of resistance 1.8 x 103Ω is used on a 240 V mains supply. (Neglect heat losses to the surrounding).
A
150.0s
B
90.0s
C
36.0s
D
20.0s
E
2.7s.
medium Difficulty
Verified Correct Answer: Option A
Physical Principles & Numerical Solution
E = V2t/R
t = ER/V2 = 4800 x 1.8 x 103/240 x 240 = 150s
Source: Myschool Past Questions Archive (Record #24287)
Physics
WAEC / WASSCE 1992
Magnetism, Electromagnetism & AC Circuits
Lenz’s law of electromagnetic induction states that
A
electromotive force is induced in a circuit whenever there is a change in the magnetic flux linked with the circuit
B
the induced current in a conductor is in such a direction as to oppose the change producing it
C
the induced e.m.f. in a circuit is proportional to the rate of change of number of lines of force linking the circuit
D
a force is exerted on a current carrying conductor in a magnetic field
E
the induced e.m.f. is proportional to the current producing the magnetic flux.
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 #24288)
Physics
WAEC / WASSCE 1992
Magnetism, Electromagnetism & AC Circuits
Which of the following statements is not correct?
A
A magnetic Held is a region where a magnetic force can be detected.
B
Magnetic fields are scalar quantities.
C
The magnitude of the magnetic force experienced by a moving charge depends on the speed on the charge.
D
the angle between the direction of the earth’s magnetic held and the horizontal is called the angle of dip.
E
Iron filings can be used to trace out the magnetic field around a bar magnet.
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 #24289)
Physics
WAEC / WASSCE 1992
Electrostatics & Capacitors
Solution
Calculate the energy stored in 20μF capacitor if the potential difference between the plates is 40 V.
A
3.2 x10-2J
B
1.6x102J
C
8.0x10-4J
D
4.0x10-4J
E
2.0x10-4J
medium Difficulty
Verified Correct Answer: Option B
Physical Principles & Numerical Solution
E = 1/2cv2 = 1/2 x 10 x 10-6 x 402 = 1.6 x 10-2J
Source: Myschool Past Questions Archive (Record #24290)
Physics
WAEC / WASSCE 1992
Current Electricity & Electric Circuits
Diagram
The diagrams above show lines of force in electric fields. In which of the diagrams would a positive test charge experience the least force as it moves from x to y?
Attached Figure / Diagram
A
I only
B
II only
C
III only
D
I and II only
E
II and III only
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 #24291)
Physics
WAEC / WASSCE 1992
Electrostatics & Capacitors
Solution
What is the electric potential at a point distance r from a proton of charge q placed in a medium of permittivity εo?
A
q2/4πεor2
B
q/4πεor2
C
q2/4πεor
D
q/4πεor
E
4πεoq2r
medium Difficulty
Verified Correct Answer: Option D
Physical Principles & Numerical Solution
The general formula for calculating electrical potential V = \(\frac{\text{W}}{\text{q}}\)
For a point charge V = \(\frac{\text{kQ}}{\text{r}}\) = \(\frac{\text{Q}}{4\pi \varepsilon_o r}\)
Source: Myschool Past Questions Archive (Record #24292)
Physics
WAEC / WASSCE 1992
Magnetism, Electromagnetism & AC Circuits
Diagram
Solution
lf the frequency of the a.c. circuit illustrated is 500Hz/ π what would be the reactance in the circuit?
Attached Figure / Diagram
A
0.01Ω
B
190.91 Ω
C
200.00 Ω
D
795.46 Ω
E
1000.00Ω
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
C1 + C = 2 + 3 = 5μF
Capacitive reactance = 1/2πfc
X = 1/2π x 500 x 5 x 10-6 = 200
Source: Myschool Past Questions Archive (Record #24293)
Physics
WAEC / WASSCE 1992
Atomic, Quantum, Nuclear Physics & Electronics
Which of the following statements is correct about cathode rays? They are fast moving
A
atoms
B
ions
C
neutrons
D
protons
E
electrons
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 #24294)
Physics
WAEC / WASSCE 1992
Atomic, Quantum, Nuclear Physics & Electronics
Which of the following gives rise to the line spectra obtained from atoms?
A
Kinetic energy of a moving atom
B
Potential energy of an electron inside an atom
C
Change of an electron from a higher to a lower energy level in the atom
D
Disturbed proton in the nucleus
E
Excitation of an electron in the atom
medium Difficulty
Verified Correct Answer: Option C
Physical Principles & Numerical Solution
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #24295)