An electric string of length l is elastically stretched through a length e by a force F. The area of cross- section of the string is A and its Young’s modulus is E. Which of the following expressions is correct?
AF = EA/eI
BF = EAI/e
CF = EAe/l
DF = EAe
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Question 2
waec1992
The process by which a metal, heated to high temperature, gives off electrons from its surface is known as
Aphotoelectric emission
Bthermionic emission
Cradioactive emission
DHeld emission
Esecondary emission
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Question 3
waec1992
A sheet of paper is placed in the path of a beam of radiations from a radioactive source. Which of the following radiations will pass through the paper?I. Alpha rays II. Beta rays III. Gamma rays
AI only
BII only
CIII only
DII and III only
EI, II and III
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Question 4
waec1992
When the nucleus of a uranium atom is split into two fragments of nearly equal mass the sum of the masses of the fragments is less than the mass of the original nucleus. This difference is a measure of the
Aexperimental error in calculating the separate masses
Bchange of momentum of each fragment
Cpotential energy lost
Dnuclear energy released
Ekinetic energy lost
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Question 5
waec1992
An element whose half-life is 3 years has N atoms. How many atoms would have decayed after 9 years
A1 N atoms8
B1 N atoms3
C2 N atoms3
D5 N atoms6
E7 N atoms8
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Question 6
waec1992
A stream of alpha particles is projected into an electric field between two plates X and Y as shown in the diagram above. Which of the following is correct? The particles are
Aaccelerated and they continue in a straight line
Bdirectionally reversed at the end of the plates
Cdeflected towards plate Y
Dattracted by both plates
Edeflected towards plate X.
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Question 7
waec1992
Which of the following gives rise to the line spectra obtained from atoms?
AKinetic energy of a moving atom
BPotential energy of an electron inside an atom
CChange of an electron from a higher to a lower energy level in the atom
DDisturbed proton in the nucleus
EExcitation of an electron in the atom
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Question 8
waec1992
Which of the following statements is correct about cathode rays? They are fast moving
Aatoms
Bions
Cneutrons
Dprotons
Eelectrons
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Question 9
waec1992
lf the frequency of the a.c. circuit illustrated is 500Hz/ π what would be the reactance in the circuit?
A0.01Ω
B190.91 Ω
C200.00 Ω
D795.46 Ω
E1000.00Ω
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Question 10
waec1992
What is the electric potential at a point distance r from a proton of charge q placed in a medium of permittivity εo?
Aq2/4πεor2
Bq/4πεor2
Cq2/4πεor
Dq/4πεor
E4πεoq2r
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Question 11
waec1992
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?
AI only
BII only
CIII only
DI and II only
EII and III only
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Question 12
waec1992
Calculate the energy stored in 20μF capacitor if the potential difference between the plates is 40 V.
A3.2 x10-2J
B1.6x102J
C8.0x10-4J
D4.0x10-4J
E2.0x10-4J
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Question 13
waec1992
Which of the following statements is not correct?
AA magnetic Held is a region where a magnetic force can be detected.
BMagnetic fields are scalar quantities.
CThe magnitude of the magnetic force experienced by a moving charge depends on the speed on the charge.
Dthe angle between the direction of the earth’s magnetic held and the horizontal is called the angle of dip.
EIron filings can be used to trace out the magnetic field around a bar magnet.
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Question 14
waec1992
Lenz’s law of electromagnetic induction states that
Aelectromotive force is induced in a circuit whenever there is a change in the magnetic flux linked with the circuit
Bthe induced current in a conductor is in such a direction as to oppose the change producing it
Cthe induced e.m.f. in a circuit is proportional to the rate of change of number of lines of force linking the circuit
Da force is exerted on a current carrying conductor in a magnetic field
Ethe induced e.m.f. is proportional to the current producing the magnetic flux.
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Question 15
waec1992
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).
A150.0s
B90.0s
C36.0s
D20.0s
E2.7s.
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Question 16
waec1992
In a domestic circuit, electrical appliances and lamps are arranged in parallel across the mains so as to enable the
Asame current to flow through the electrical appliances and the lamps
Bmaximum energy to be consumed at least cost
Csame fuse to be used for the electrical appliances and the lamps
Dvoltage across the appliances not to be affected when the lamps are switched on and off
Eheat losses to be minimized
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Question 17
waec1992
Calculate the length of a constantan wire of cross- sectional area 4 π x 10-8m2 and resistivity 1.1 x 10-6 Ω m required to construct a standard resistor of resistance 21 Ω. [Take π = 22/7]
A0.42m
B2.40 m
C6.25 m
D183.75 m
E590.00 m
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Question 18
waec1992
Which of the following is not a consequence of hydrogen bubbles covering the copper plate of a primary cell?
APolarization
BLocal action
CFormation of hydrogen electrode
DIncrease in the resistance of the cell
EGeneration of less current by the cell
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Question 19
waec1992
Calculate the rate at which energy is used up in the circuit illustrated by the diagram
A0 W
B2 W
C4 W
D8 W
E16 W
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Question 20
waec1992
A negatively charged rod is brought near the cap of a gold-leaf electroscope. The cap is earthed momentarily while the rod is near to it. The rod is then removed. Which of the following is correct?
AThe cap will be positively charged and the negatively charged leaves will diverge
BThe cap will be negatively charged and the positively charged leaves will diverge
CThe cap and the leaves will be positively charged
DThe cap and the leaves will be negatively charged.
EThe leaves will not diverge because the cap has been earthed.
