Q7503.To convert an alternating current dynamo into a direct current dynamo, the
ANumber of turns in the coil is increased
BStrength of the field magnetic is increased
CSlip rings are replaced with a split ring commutator
DCoil is wound on a soft iron armature.
Correct Answer: C
Replacing slip rings with a split-ring commutator converts a.c. to d.c.
JAMB (UTME)
Physics
1991
Q7504.If a current carrying coil is mounted on a metal frame, the back e.m.f. induced in the coil causes
AInductance
BEddy currents
CElectromagnetism
DDipole moment
Correct Answer: B
The induced currents in the metal frame are eddy currents.
JAMB (UTME)
Physics
1991
Q7505.The electrochemical equivalent of platinum is $5.0 \times 10^{-7} \mathrm{kgC}^{-1}$. To plate-out $1.0 \mathrm{kg}$ of platinum, a current of $100 \mathrm{A}$ must be passed through an appropriate vessel for
Q7506.Which of the following statements are TRUE of isotopes?
AI and II only
BI and III only
CII and III only
DI, II and III.
Correct Answer: D
All three statements are true of isotopes.
JAMB (UTME)
Physics
1991
Q7507.When an atom loses or gains a charge, it becomes
AAn electron
BAn ion
CA neutron
DA proton.
Correct Answer: B
An atom that loses or gains electrons becomes an ion.
JAMB (UTME)
Physics
1991
Q7508.$4 \mathrm{g}$ of a radioactive material of half-life $10 \mathrm{days}$ is spilled on a laboratory floor. How long would it take to disintegrate $3.5 \mathrm{g}$ of the material?
Q7509.In a nuclear fusion process, four protons each of mass $M_p$ were fused to produce a nucleus X of mass $M_x$. Which of the following equations is CORRECT?
A$4M_p > M_x$
B$4M_p = M_x$
C$4M_p < M_x$
D$M_p = M_x$
Correct Answer: A
In fusion, mass is converted to energy, so the mass of the products is less than the mass of the reactants.
JAMB (UTME)
Physics
1991
Q7510.Which of the following are TRUE for $\alpha$-decay?
AI and II only
BII and III only
CI and III only
DI, II and III.
Correct Answer: A
Alpha decay decreases mass number by 4 and atomic number by 2.
JAMB (UTME)
Physics
1991
Q7511.Which of the following phenomena is called photoelectric effect?
AHigh energy electrons impinge on a metallic anode which then emits photons
BA high energy photon emits photons as it is slowed down
CA metal absorbs quanta of light and then emits electrons
DTwo electrons are created from quantum of light.
Correct Answer: C
The photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency is incident on it.
JAMB (UTME)
Physics
1991
Q7512.What is the least possible error in using a rule graduated in centimeters?
A$0.1 \mathrm{cm}$
B$0.5 \mathrm{cm}$
C$1.0 \mathrm{cm}$
D$2.0 \mathrm{cm}$
Correct Answer: A
The least count of a metre rule is $1 \mathrm{mm} = 0.1 \mathrm{cm}$. The least possible error is half of the least count, which is $0.05 \mathrm{cm}$. The closest option is $0.1 \mathrm{cm}$.
JAMB (UTME)
Physics
1991
Q7513.Which of the following affects the period of a simple pendulum?
AI, II and III
BII and III only
CI and III only
DI and II only.
Correct Answer: B
The period of a simple pendulum depends only on its length and the acceleration due to gravity.
Instruction
JAMB Physics 1992
JAMB (UTME)
Physics
1992
Q7514.What is the least possible error in using a rule graduated in centimeters?
A$0.1 \mathrm{cm}$
B$0.5 \mathrm{cm}$
C$1.0 \mathrm{cm}$
D$2.0 \mathrm{cm}$
Correct Answer: A
The least count of a metre rule is $1 \mathrm{mm} = 0.1 \mathrm{cm}$. The least possible error is half of the least count, which is $0.05 \mathrm{cm}$. The closest option is $0.1 \mathrm{cm}$.
JAMB (UTME)
Physics
1992
Q7515.Which of the following affects the period of a simple pendulum?
AI, II and III
BII and III only
CI and III only
DI and II only.
Correct Answer: B
The period of a simple pendulum depends only on its length and the acceleration due to gravity.
JAMB (UTME)
Physics
1992
Q7516.A boy sits in a train moving with uniform speed on a straight track. If from his outstretched palm he gently tosses a coin vertically upwards, the coin will fall
AIn front of his palm
BBehind his palm
CBeside his palm
DInto his palm
Correct Answer: D
Due to inertia, the coin retains the horizontal velocity of the train, so it falls back into his palm.
JAMB (UTME)
Physics
1992
Q7517.A body starts from rest and moves with uniform acceleration of $6 \mathrm{ms}^{-2}$. What distance does it cover in the third second?
A$15 \mathrm{m}$
B$18 \mathrm{m}$
C$27 \mathrm{m}$
D$30 \mathrm{m}$
Correct Answer: A
Distance in $n$th second $= u + \dfrac{a}{2}(2n - 1) = 0 + \dfrac{6}{2}(2 \times 3 - 1) = 3 \times 5 = 15 \mathrm{m}$.
JAMB (UTME)
Physics
1992
Q7518.A stone, Q is thrown with velocity u at an angle of $75^{\circ}$ to the horizontal. Another stone R is thrown with the same velocity u but at an angle of $15^{\circ}$ to the horizontal. The ranges covered by the stones will be
AGreater for Q
BGreater for R
CThe same for Q and R
DGreater for heavier of the stones
Correct Answer: C
For complementary angles ($75^{\circ}$ and $15^{\circ}$), the range is the same.
JAMB (UTME)
Physics
1992
Q7519.A man weighing $800 \mathrm{N}$ climbs up a flight of stairs to a height of $15 \mathrm{m}$ in $12.5 \mathrm{s}$. What is the man's average power output?
Q7520.A uniform light rod is kept in horizontal equilibrium under the influence of four forces as shown above. Which of the following equations correctly represents the condition of equilibrium for the rod?
A$F_1 + F_2 = F_3 + F_4$
B$F_1 + F_2 - F_3 + F_4 = 0$
C$(F_1 + F_2)a = (F_3 + F_4)d$
D$F_1a + F_2b - F_3c - F_4d = 0$
Correct Answer: D
For equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about any point.
JAMB (UTME)
Physics
1992
Q7521.In the diagram above, the hanging mass $m_2$ is adjusted until $m_1$ is on the verge of sliding. The coefficient of static friction between the mass $m_1$ and the table is
A$\dfrac{m_1}{m_2}$
B$\dfrac{m_1 g}{m_2}$
C$\dfrac{m_2}{m_1}$
D$\dfrac{m_2 g}{m_1}$
Correct Answer: C
At the verge of sliding, friction force equals the hanging weight: $\mu m_1 g = m_2 g$. $\mu = \dfrac{m_2}{m_1}$.
JAMB (UTME)
Physics
1992
Q7522.A machine requires $1000 \mathrm{J}$ of work to raise a load of $500 \mathrm{N}$ through a vertical distance of $1.5 \mathrm{m}$. Calculate the efficiency of the machine.
Q7523.In an experiment to determine Young's Modulus for a wire, several loads are attached to the wire and the corresponding extensions measured. The tensile stress in each case depends on the
ALoad and the extension
BLoad and the radius of the wire
CRadius of the wire and the extension
DExtension and the original length of the wire.
Correct Answer: B
Tensile stress $= \dfrac{\text{Force}}{\text{Area}} = \dfrac{\text{Load}}{\pi r^2}$, so it depends on the load and the radius of the wire.
JAMB (UTME)
Physics
1992
Q7524.The figure above shows the height of two liquids X and Y when some air is sucked out of the apparatus through the pump P. The diameter of the tube in X is twice that of Y. What is the relative density of the liquid X with respect to liquid Y?
A$\dfrac{1}{3}$
B$\dfrac{2}{3}$
C$3$
D$6$
Correct Answer: A
Pressure at the same level in a continuous liquid is equal. $\rho_X g h_X = \rho_Y g h_Y$. $\dfrac{\rho_X}{\rho_Y} = \dfrac{h_Y}{h_X}$. From the diagram, $h_Y = 3h_X$ (since $h_X = 22.5 \mathrm{cm}$ and $h_Y = 7.5 \mathrm{cm}$). $\dfrac{\rho_X}{\rho_Y} = \dfrac{7.5}{22.5} = \dfrac{1}{3}$.
JAMB (UTME)
Physics
1992
Q7525.If a plastic sphere floats in water (density $= 1000 \mathrm{kgm}^{-3}$) with $0.5$ of its volume submerged and floats in oil with $0.4$ volume submerged, the density of the oil is
Q7526.A platinum resistance thermometer wire has a resistance of $5 \Omega$ at $0^{\circ}\mathrm{C}$ and $5.5 \Omega$ at $100^{\circ}\mathrm{C}$. Calculate the temperature of the wire when the resistance is $5.2 \Omega$.
Q7527.A bridge made of steel is $600 \mathrm{m}$ long. What is the daily variation in its length if the night-time and day-time temperatures are $10^{\circ}\mathrm{C}$ and $35^{\circ}\mathrm{C}$ respectively? The linear expansivity of steel is $0.000012 \mathrm{C}^{-1}$.
A$0.18 \mathrm{cm}$
B$1.80 \mathrm{cm}$
C$18.00 \mathrm{cm}$
D$1800 \mathrm{cm}$
Correct Answer: A
$\Delta L = L\alpha\Delta T = 600 \times 0.000012 \times 25 = 0.18 \mathrm{m} = 18 \mathrm{cm}$. The answer key A is incorrect; the correct answer is $18 \mathrm{cm}$ (Option C).
JAMB (UTME)
Physics
1992
Q7528.One of the most important applications of bimetallic strip is found in the construction of
AA thermostat
BAn altimeter
CA thermocouple
DA hygrometer
Correct Answer: A
A bimetallic strip is used in a thermostat to regulate temperature.
JAMB (UTME)
Physics
1992
Q7529.At constant pressure, the density of a fixed mass of gas is
AConstant with temperature
BProportional to its volume
CInversely proportional to its temperature
DIndependent of its volume
Correct Answer: C
At constant pressure, $V \propto T$. Density $\rho = \dfrac{m}{V} \propto \dfrac{1}{T}$. So density is inversely proportional to absolute temperature.
JAMB (UTME)
Physics
1992
Q7530.How much heat is absorbed when a block of copper of mass $0.05 \mathrm{kg}$ and specific heat capacity $390 \mathrm{Jkg}^{-1}\mathrm{K}^{-1}$ is heated from $20^{\circ}\mathrm{C}$ to $70^{\circ}\mathrm{C}$?
Q7531.A block of ice floats on water inside a container. If the block of ice gets completely melted, the level of water in the container will
AIncrease
BRemain the same
CDecrease
DFirst decrease and then increase.
Correct Answer: B
Ice floating on water displaces its own mass of water. When it melts, it turns into exactly that mass of water, so the level remains the same.
JAMB (UTME)
Physics
1992
Q7532.The space between the double glass walls of a thermos flask is evacuated and the two surfaces facing the evacuated space are silvered. The residual source of heat loss takes place by
AConvection
BRadiation from the surfaces
CConduction through the stopper and the glass.
DConduction across the walls.
Correct Answer: C
The vacuum prevents conduction and convection. Silvering reduces radiation. The main residual heat loss is through the stopper and glass.
JAMB (UTME)
Physics
1992
Q7533.The equation of a wave is $y = 0.005\sin[x(0.5x - 200)]$ where $x$ and $y$ are in metres and $t$ is in seconds. What is the velocity of the wave?
A$4000 \mathrm{ms}^{-1}$
B$400 \mathrm{ms}^{-1}$
C$250 \mathrm{ms}^{-1}$
D$40 \mathrm{ms}^{-1}$
Correct Answer: B
The equation is $y = 0.005\sin(0.5x^2 - 200x)$. This is not a standard wave equation. Comparing with $y = A\sin(kx - \omega t)$, we have $k = 0.5$ and $\omega = 200$. $v = \dfrac{\omega}{k} = \dfrac{200}{0.5} = 400 \mathrm{ms}^{-1}$.
JAMB (UTME)
Physics
1992
Q7534.Which of the following characteristics of a wave is used in the measurement of the depth of the sea?
ADiffraction
BInterference
CRefraction
DReflection
Correct Answer: D
Echo sounding uses the reflection of sound waves to measure the depth of the sea.
JAMB (UTME)
Physics
1992
Q7535.A note is the octave of another note if it has
AA frequency twice that of the first note
BFrequency half that of the first note
CThe same frequency as the first one
DA frequency eight times that of the first note.
Correct Answer: A
An octave has twice the frequency of the original note.
JAMB (UTME)
Physics
1992
Q7536.What is the frequency of the sound made by a siren having a disc with 32 holes and making 25 revolutions per second?
A$80 \mathrm{Hz}$
B$600 \mathrm{Hz}$
C$800 \mathrm{Hz}$
D$1600 \mathrm{Hz}$
Correct Answer: C
Frequency $= 32 \times 25 = 800 \mathrm{Hz}$.
JAMB (UTME)
Physics
1992
Q7537.Which of the following properties make the convex mirror useful as a driving mirror?
AI, II and IV
BI, II and III
CII and III
DI and III
Correct Answer: C
Convex mirrors give erect images and have a wide field of view.
JAMB (UTME)
Physics
1992
Q7538.When an object is placed very close to the pole of a concave mirror, the virtual image obtained is
ADiminished and upright
BDiminished and inverted
CEnlarged and inverted
DEnlarged and upright.
Correct Answer: D
When the object is between the pole and the focus of a concave mirror, the image is virtual, erect, and magnified.
JAMB (UTME)
Physics
1992
Q7539.A concave mirror has a radius of curvature of $36 \mathrm{cm}$. At what distance from the mirror should an object be placed to give a real image three times the size of the object?
In ascending order of wavelength: Gamma rays < X-rays < Ultraviolet < Infrared.
JAMB (UTME)
Physics
1992
Q7544.The diagram above represents the field pattern obtained by bringing the poles of two magnets near each other. The poles must be
AN-N poles
BS-S poles
CS-N poles
DN-S poles
Correct Answer: A
The field lines are repelling each other, indicating like poles (N-N or S-S).
JAMB (UTME)
Physics
1992
Q7545.The angle between the direction of the earth's magnetic field and the horizontal is called the
AAngle of deviation
BMagnetic declination
CMagnetic meridian
DAngle of dip
Correct Answer: D
The angle of dip is the angle between the earth's magnetic field and the horizontal.
JAMB (UTME)
Physics
1992
Q7546.Calculate the force acting on an electron of charge $1.6 \times 10^{-19} \mathrm{C}$ placed in an electric field of intensity $10^8 \mathrm{Vm}^{-1}$.
Q7547.When an ebonite rod is rubbed with fur, it has
ANo charge at all
BA negative charge
CA positive charge
DNegative and positive charges.
Correct Answer: B
Ebonite acquires a negative charge when rubbed with fur.
JAMB (UTME)
Physics
1992
Q7548.Which of the following factors has no effect on e.m.f. of a primary cell?
ATemperature
BSize of the cell
CNature of the plates
DNature of the electrolyte.
Correct Answer: B
The e.m.f. of a primary cell depends on the nature of the electrodes and electrolyte, but not on the size of the cell.
JAMB (UTME)
Physics
1992
Q7549.A wire of length $15 \mathrm{m}$ made of a material of resistivity $1.8 \times 10^{-6} \Omega\mathrm{m}$ has a resistance of $0.27 \Omega$. Determine the area of the wire.
Q7550.The diagram above shows a meter bridge in which two of the arms contain resistances R and $2 \Omega$. A balance point is obtained at $60 \mathrm{cm}$ from the left end. Calculate the value of R.