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?
A1.48ev
B2.21ev
C4.42ev
D5.75ev
E11.51ev
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Question 852
waec1991
The half-life of a radioactive substance is 2 seconds. Calculate the decay constant
A0.035s-1
B0.151s-1
C0.347s-1
D0.576s-1
E1.386s-1
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Question 853
waec1991
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
A4.0 x 10-26J
B4.0 x 10-21J
C6.4 x 10-20J
D3.2 x 10-15J
E2.5 x 10-20J
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Question 854
waec1991
When a metal surface is irradiated, photoelectrons may be ejected from the metal. The kinetic energy of the ejected electrons depends on the
Asorce of the radiation
Bintensity of the radiation
Cdetection device for the electrons
Damplitude of the radiation
Efrequency of the radiation
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Question 855
waec1991
plane as 63cm of HG while a ground observer records a reading of 75cm of Hg with his barometer. assuming that the density of air is constant, calculate the height of the plane above the ground. (Take the relative densities of air and mecury as 0.00136 and 13.6 respectively
A120m
B138m
C1200m
D274m
E120,000m
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Question 856
waec1991
Which of the following statements is not correct? Isotopes of an element have
Athe same number of electric charges on the nucleus
Bthe same chemical properties
Cdifferent nucleon numbers
Ddifferent proton numbers
Edifferent atomic masses
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Question 857
waec1991
Which of the following statements above viscosity are correct? when a ball falls through a viscous liquid i. viscosity opposes the gravitational force on the ball. ii. viscosity opposes the upthrust on the ball. iii. viscosity is in the same direction as the upthrust on the ball. iv. as the ball falls faster the more viscous the liquid is
Ai and iii only
Bi and ii only
Cii and iv only
Diii and iv only
Ei, ii and iv only
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Question 858
waec1991
The unit of stress is
ANm
BN
CNm-2
DNm2
ENm1
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Question 859
waec1991
An induction coil is generally used to?
Arectify an alternating current
Bproduce a large input voltage
Csmoothen a pulsating direct current
Dmodulate an incoming signal
Eproduce a large output voltage
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Question 860
waec1991
The diagram above shows a current carrying wire between the poles of a magnet. In which direction would the wire tend to move?
Ainto the paper
Bout of the paper
Ctowargs the north pole of the magnet
Dtowards the south pole of the magnet
Etowards the top of the pages
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Question 861
waec1991
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
A30
B240
C248
D450
E1248
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Question 862
waec1991
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
AL1 becomes brighter and L2 becomes dimmer
BL1 becomes brighter and L2 does not change
CL2 becomes dimmer and L1 does not change
DL1 becomes dimmer and L2 does not change
EL1 and L2 becomes brighter
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Question 863
waec1991
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.
A2.81jg-1
B6.25Jg-1
C8.89Jg-1
D168.75Jg-1
E5333.33Jg-1
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Question 864
waec1991
Using the data in the circuit illustrated above, calculate the value of R
A0.02\(\Omega\)
B0.05\(\Omega\)
C5.00\(\Omega\)
D20.00\(\Omega\)
E50.00\(\Omega\)
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Question 865
waec1991
Which of the following is stored by dry Leclanche cell?
Achemical energy
Bnuclear energy
Csolar energy
Dheat energy
Eelectrical energy
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Question 866
waec1991
In which of the points labelled A, B, C, D and E on the conductor shown would electric charge tend to concentrate most?
AA
BB
CC
DD
EE
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Question 867
waec1991
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
A\(\frac{1}{2}\)W
B\(\frac{2}{3}\)W
CW
D2w
E3W
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Question 868
waec1991
Two objects of masses 80kg and 50kg are separated by a distance of 0.2m. If the gravitational constant is 6.6 x 10-11Nm
A4.9 x 10-9N
B1.3 x 10-6N
C6.6 x 10-8N
D6.6 x 10-6N
E2.6 x 10-9N
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Question 869
waec1991
If the frequency of the e.m.f. source in the a.c. circuit illustrated above is \(\frac{500}{\pi}\)Hz. What is the reactance of the inductor?
A450
B0.9
C900
D567
E43
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Question 870
waec1991
A particle of charge q and mass m moving with a velocity v enters a uniform magnetic field b in the direction of the field. The force on the particle is
