Q7457.The number of neutrons contained in the nucleus of $^{238}_{92}\mathrm{U}$ is
A$92$
B$146$
C$238$
D$330$
Correct Answer: B
Number of neutrons $= 238 - 92 = 146$.
JAMB (UTME)
Physics
1990
Q7458.What precaution should a manufacturer take to ensure that energy loss in a transformer is minimized?
AThe winding of the transformer should be made of high resistance wires.
BThe core should be made of thin sheets of metal.
CNo magnetic material should be used to make the core.
DThe flux linking the primary with the secondary coils should be minimum.
Correct Answer: B
Laminated thin sheets reduce eddy current losses.
JAMB (UTME)
Physics
1990
Q7459.A substance has a half-life of $3 \mathrm{min}$. After $6 \mathrm{min}$, the count rate was observed to be $400$. What was its count rate at zero time?
Q7460.Which of the following graphs represents a voltage-current characteristic curve for a diode?
A[Graph A]
B[Graph B]
C[Graph C]
D[Graph D]
Correct Answer: C
A diode conducts in forward bias (curve rising) and blocks in reverse bias (curve near zero).
JAMB (UTME)
Physics
1990
Q7461.The photocell works on the principle of the
AVoltaic cell
BEmission of electrons by incident radiation
CEmission of protons by incident electrons
DEmission of photons by incident electrons.
Correct Answer: B
A photocell works on the photoelectric effect, where electrons are emitted by incident radiation.
JAMB (UTME)
Physics
1990
Q7462.Which of the following is the most suitable for use as an altimeter?
AA mercury barometer
BA fortin barometer
CA mercury manometer
DAn aneroid barometer.
Correct Answer: D
An aneroid barometer is portable and suitable for use as an altimeter.
JAMB (UTME)
Physics
1990
Q7463.A body of weight W N rests on a smooth plane inclined at an angle $\theta^{\circ}$ to the horizontal. What is the resolved part of the weight in newtons along the plane?
A$W\sin\theta$
B$W\cos\theta$
C$W\sec\theta$
D$W\tan\theta$
Correct Answer: A
The component of weight along the inclined plane is $W\sin\theta$.
Instruction
JAMB Physics 1991
JAMB (UTME)
Physics
1991
Q7464.A small metal ball is thrown vertically upwards from the top of a tower with an initial velocity of $20 \mathrm{ms}^{-1}$. If the ball took a total of $6 \mathrm{s}$ to reach ground level, determine the height of the tower. $[g = 10 \mathrm{ms}^{-2}]$
A$60 \mathrm{m}$
B$80 \mathrm{m}$
C$100 \mathrm{m}$
D$120 \mathrm{m}$
Correct Answer: A
Taking upward as positive: $s = ut + \dfrac{1}{2}at^2 = 20(6) + \dfrac{1}{2}(-10)(6^2) = 120 - 180 = -60 \mathrm{m}$. The negative sign indicates displacement is downward, so the height of the tower is $60 \mathrm{m}$.
JAMB (UTME)
Physics
1991
Q7465.An object moves with uniform speed round a circle. Its acceleration has
AConstant magnitude and constant direction.
BConstant magnitude and varying direction.
CVarying magnitude and constant direction.
DVarying magnitude and varying direction.
Correct Answer: B
In uniform circular motion, the magnitude of acceleration (centripetal) is constant but its direction is always towards the center, which changes continuously.
JAMB (UTME)
Physics
1991
Q7466.A body of mass $100 \mathrm{g}$ moving with a velocity of $10.0 \mathrm{ms}^{-1}$ collides with a wall. If after the collision, it moves with a velocity of $2.0 \mathrm{ms}^{-1}$ in the opposite direction, calculate the change in momentum.
A$0.8 \mathrm{Ns}$
B$1.2 \mathrm{Ns}$
C$12.0 \mathrm{Ns}$
D$80.0 \mathrm{Ns}$
Correct Answer: B
$\Delta p = m(v - u) = 0.1(-2.0 - 10.0) = 0.1(-12) = -1.2 \mathrm{Ns}$. The magnitude of change in momentum is $1.2 \mathrm{Ns}$.
JAMB (UTME)
Physics
1991
Q7467.Find the tension $T_1$ in the diagram above if the system is in equilibrium. $[g = 10 \mathrm{ms}^{-2}]$
Q7468.A spring of force constant $1500 \mathrm{Nm}^{-1}$ is acted upon by a constant force of $75 \mathrm{N}$. Calculate the potential energy stored in the spring.
Q7469.A wheel and axle have radii $80 \mathrm{cm}$ and $10 \mathrm{cm}$ respectively. If the efficiency of the machine is $0.85$, an applied force of $1200 \mathrm{N}$ to the wheel will raise a load of
Q7470.A body is under the action of a force F such that the force-displacement graph of the body is semicircular as shown above. The work done on the body by the force in moving through $24 \mathrm{m}$ is
A$36\pi \mathrm{J}$
B$72\pi \mathrm{J}$
C$144\pi \mathrm{J}$
D$288\pi \mathrm{J}$
Correct Answer: B
Work done = area under graph = area of semicircle = $\dfrac{1}{2}\pi r^2$. The maximum force is $12 \mathrm{N}$, so radius $r = 12$. Area $= \dfrac{1}{2} \times \pi \times 12^2 = 72\pi \mathrm{J}$.
JAMB (UTME)
Physics
1991
Q7471.A $20 \mathrm{kg}$ mass is to be pulled up a slope inclined at $30^{\circ}$ to the horizontal. If the efficiency of the plane is $75\%$, the force required to pull the load up the plane is
Q7472.The spiral spring of a spring balance is $25.0 \mathrm{cm}$ long when $5 \mathrm{N}$ hangs on it and $30.0 \mathrm{cm}$ long when the weight is $10 \mathrm{N}$. What is the length of the spring if the weight is $3 \mathrm{N}$ assuming Hooke's Law is obeyed?
Q7473.The mass of a stone is $15.0 \mathrm{g}$ when completely immersed in water and $10.0 \mathrm{g}$ when completely immersed in a liquid of relative density 2.0. The mass of the stone in air is
A$5.0 \mathrm{g}$
B$12.0 \mathrm{g}$
C$20.0 \mathrm{g}$
D$25.0 \mathrm{g}$
Correct Answer: C
Upthrust in liquid $= 2 \times$ upthrust in water. Let mass in air be $m$. $(m - 10) = 2(m - 15)$. $m - 10 = 2m - 30$. $m = 20 \mathrm{g}$.
JAMB (UTME)
Physics
1991
Q7474.A pilot records the atmospheric pressure outside his plane as $63 \mathrm{cm}$ of Hg while a ground observer records a reading of $75 \mathrm{cm}$ of Hg for the atmospheric pressure on the ground. Assuming that the density of the atmosphere is constant, calculate the height of the plane above the ground. (Relative density of Hg $= 13.0$ and that of air $= 0.00013$)
A$1200 \mathrm{m}$
B$6300 \mathrm{m}$
C$7500 \mathrm{m}$
D$12800 \mathrm{m}$
Correct Answer: A
Pressure difference $= (75 - 63) = 12 \mathrm{cmHg} = 12 \times 13.0 \mathrm{cm}$ of air $= 156 \mathrm{cm}$ of air. $h = 156 \mathrm{cm} = 1.56 \mathrm{m}$. This is incorrect. Let's use $P = \rho g h$. $\Delta P = \rho_{air} g h$. $\rho_{Hg} = 13 \times 1000 = 13000 \mathrm{kgm}^{-3}$. $\rho_{air} = 0.00013 \times 1000 = 0.13 \mathrm{kgm}^{-3}$. $\Delta P = 12 \mathrm{cmHg} = 0.12 \times 13000 \times 10 = 15600 \mathrm{Pa}$. $h = \dfrac{\Delta P}{\rho_{air} g} = \dfrac{15600}{0.13 \times 10} = 12000 \mathrm{m}$. The answer key A is incorrect; the correct answer is $12000 \mathrm{m}$.
JAMB (UTME)
Physics
1991
Q7475.In which of the following is surface tension important?
AThe floating of a ship in water
BThe floating of a dry needle in water
CThe floating of a balloon in air
DThe diffusion of a sugar solution across membrane.
Correct Answer: B
A dry needle can float on water due to surface tension.
JAMB (UTME)
Physics
1991
Q7476.A thermometer with an arbitrary scale, S, of equal divisions registers $-30^{\circ}\mathrm{S}$ at the ice point and $+90^{\circ}\mathrm{S}$ at the steam point. Calculate the Celsius temperature corresponding to $60^{\circ}\mathrm{S}$.
Q7477.A brass rod is $2 \mathrm{m}$ long at a certain temperature. What is the length for a temperature rise of $100 \mathrm{K}$, if the expansivity of brass is $18 \times 10^{-6} \mathrm{K}^{-1}$?
Q7478.What is the difference in the amount of heat given out by $4 \mathrm{kg}$ of steam and $4 \mathrm{kg}$ of water when both are cooled from $100^{\circ}\mathrm{C}$ to $80^{\circ}\mathrm{C}$? [The specific latent heat of steam is $2,260,000 \mathrm{Jkg}^{-1}$, specific heat capacity of water is $4200 \mathrm{Jkg}^{-1}\mathrm{K}^{-1}$]
A$4,200 \mathrm{J}$
B$2,260,000 \mathrm{J}$
C$9,040,000 \mathrm{J}$
D$9,380,000 \mathrm{J}$
Correct Answer: C
Steam gives out latent heat on condensing: $Q_1 = 4 \times 2260000 = 9040000 \mathrm{J}$. Both then cool: $Q_2 = 4 \times 4200 \times 20 = 336000 \mathrm{J}$. Difference $= 9040000 \mathrm{J}$.
JAMB (UTME)
Physics
1991
Q7479.The graphs below show the variation of volume (V) against temperature (T) in Kelvin for a given mass of gas at constant pressure. Which of the graphs depicts the behavior of an ideal gas?
A[Graph A]
B[Graph B]
C[Graph C]
D[Graph D]
Correct Answer: A
For an ideal gas at constant pressure, volume is directly proportional to absolute temperature, giving a straight line through the origin.
JAMB (UTME)
Physics
1991
Q7480.How long does it take a $750 \mathrm{W}$ heater to raise the temperature of $1 \mathrm{kg}$ of water from $20^{\circ}\mathrm{C}$ to $50^{\circ}\mathrm{C}$? [Specific heat capacity of water $= 4200 \mathrm{Jkg}^{-1}\mathrm{K}^{-1}$]
Q7481.The saturated vapour pressure of a liquid increases as the
AVolume of the liquid increases
BVolume of the liquid decreases
CTemperature of the liquid increases
DTemperature of the liquid decreases
Correct Answer: C
Saturated vapour pressure increases with temperature.
JAMB (UTME)
Physics
1991
Q7482.The absolute temperature of a perfect gas is proportional to the average
APotential energy of the molecules
BSeparation between the molecules
CKinetic energy of the molecules
DVelocity of the molecules.
Correct Answer: C
Absolute temperature is a measure of the average kinetic energy of the molecules.
JAMB (UTME)
Physics
1991
Q7483.A room is heated by means of a charcoal fire. An occupant of the room standing away from the fire is warmed mainly by
AConvection
BRadiation
CConduction
DReflection
Correct Answer: B
Heat from a fire reaches a person standing away mainly by radiation.
JAMB (UTME)
Physics
1991
Q7484.A boy timed 30 oscillations of a certain pendulum thrice and obtained $1 \mathrm{min}. 10 \mathrm{s}$, $1 \mathrm{min}. 12 \mathrm{s}$ and $1 \mathrm{min}. 7 \mathrm{s}$ respectively. The mean period of oscillation of the pendulum is
A$0.14 \mathrm{s}$
B$0.43 \mathrm{s}$
C$2.32 \mathrm{s}$
D$6.97 \mathrm{s}$
Correct Answer: C
Mean time $= \dfrac{70 + 72 + 67}{3} = \dfrac{209}{3} = 69.67 \mathrm{s}$. Period $= \dfrac{69.67}{30} = 2.32 \mathrm{s}$.
JAMB (UTME)
Physics
1991
Q7485.Which of the following is TRUE of light and sound waves?
AThey both transmit energy
BThey both need a medium for propagation
CThey are both transverse waves
DTheir velocities in air are equal.
Correct Answer: A
Both light and sound waves transmit energy. Sound needs a medium; light does not.
JAMB (UTME)
Physics
1991
Q7486.The image in a pin-hole camera is
AErect and formed by refraction through a lens
BVirtual and formed by dispersion
CErect and gets sharper as the hole becomes larger
DInverted and formed by the light from each point traveling in a straight line.
Correct Answer: D
The image in a pin-hole camera is inverted and formed by rectilinear propagation of light.
JAMB (UTME)
Physics
1991
Q7487.When a plane mirror at which a ray is incident is rotated through an angle $\theta$, the reflected ray will be rotated through
A$\dfrac{1}{2}\theta$
B$\theta$
C$2\theta$
D$3\theta$
Correct Answer: C
When a mirror is rotated by angle $\theta$, the reflected ray rotates by $2\theta$.
JAMB (UTME)
Physics
1991
Q7488.A trough $12.0 \mathrm{cm}$ deep is filled with water of refractive index $\dfrac{4}{3}$. By how much would a coin at the bottom of the trough appear to be displaced when viewed vertically from above the water surface?
Q7489.In a ray diagram for a thin converging lens, a ray that is not parallel to the optic axis but passes through the optic center will
APass through undeviated
BPass through the center of curvature after refraction
CEmerge parallel to the principal axis
DPass through the principal focus after refraction.
Correct Answer: A
A ray passing through the optical center of a thin lens passes through undeviated.
JAMB (UTME)
Physics
1991
Q7490.Which of the following correctly describes the image of an object, $4 \mathrm{cm}$ from a diverging lens of focal length $-12 \mathrm{cm}$?
AThe image is virtual, $3 \mathrm{cm}$ in front of the lens
BThe image is real, $6 \mathrm{cm}$ behind the lens
CThe image is virtual, $6 \mathrm{cm}$ in front of the lens
DThe image is real, $3 \mathrm{cm}$ in front of the lens.
Correct Answer: A
$\dfrac{1}{f} = \dfrac{1}{u} + \dfrac{1}{v}$. $\dfrac{1}{-12} = \dfrac{1}{4} + \dfrac{1}{v}$. $\dfrac{1}{v} = -\dfrac{1}{12} - \dfrac{1}{4} = -\dfrac{4}{12} = -\dfrac{1}{3}$. $v = -3 \mathrm{cm}$. Image is virtual, $3 \mathrm{cm}$ from lens on same side as object.
JAMB (UTME)
Physics
1991
Q7491.Two tuning forks of frequencies $256 \mathrm{Hz}$ and $260 \mathrm{Hz}$ are sounded close to each other. What is the frequency of the beats produced?
Q7492.A man hears his echo from a nearby hill $2 \mathrm{s}$ after he shouted. If the frequency of his voice is $260 \mathrm{Hz}$ and the wavelength is $1.29 \mathrm{m}$, how far away is the hill?
Q7493.When the bottom tip of a vibrating tuning fork is held in contact with a wooden box, a louder sound is heard. This phenomenon is known as
ABeats
BEchoing
CResonance
DReverberation
Correct Answer: C
The wooden box resonates with the tuning fork, amplifying the sound.
JAMB (UTME)
Physics
1991
Q7494.Which of the following statements is CORRECT about the earth's magnetic field?
AThe angle of dip is the angle which a freely suspended magnet makes with the vertical
BThe angle of declination is the angle between the magnetic meridian and the geographic meridian
CThe angle of declination is the angle which a magnetic compass makes with the magnetic meridian.
DThe angle of inclination is the difference between the angle of dip and the angle of declination.
Correct Answer: B
The angle of declination is the angle between the magnetic meridian and the geographic meridian.
JAMB (UTME)
Physics
1991
Q7495.An insulated rod when rubbed with a material acquires
AA negative charge if it is made of glass and rubbed with silk
BNo charge if it is made of glass and rubbed with fur
CNo charge if it is made of copper and rubbed with silk
DA positive charge if it is made of copper and rubbed with fur.
Correct Answer: B
Glass rubbed with fur acquires a positive charge, not no charge. (The answer key B is incorrect; the correct statement is that glass rubbed with silk acquires a positive charge).
JAMB (UTME)
Physics
1991
Q7496.The internal resistance of each of the cells $E_1$ and $E_2$ shown in the figure above is $2 \Omega$. Calculate the total current in the circuit.
A$0.80 \mathrm{A}$
B$0.50 \mathrm{A}$
C$0.40 \mathrm{A}$
D$0.004 \mathrm{A}$
Correct Answer: B
The two cells are in parallel, so $E = 2 \mathrm{V}$, $r = 1 \Omega$. Total resistance $= 1 + 3 = 4 \Omega$. $I = \dfrac{E}{R + r} = \dfrac{2}{4} = 0.5 \mathrm{A}$.
JAMB (UTME)
Physics
1991
Q7497.The function of the system of granulated carbon mixed with manganese (IV) oxide in a Leclanche cell is to
AIncrease the e.m.f. of the cell to $2.0 \mathrm{V}$
BPrevent local action in the cell
CPrevent polarization in the cell
DMake the cell black and hence a good radiator
Correct Answer: C
Manganese(IV) oxide is a depolarizer that prevents polarization in the Leclanche cell.
JAMB (UTME)
Physics
1991
Q7498.A moving coil galvanometer of $300 \Omega$ resistance gives full scale deflection for $1.0 \mathrm{mA}$. The resistance, R, of the shunt that is required to convert the galvanometer into a $3.0 \mathrm{A}$ ammeter is
Q7500.The net capacitance in the circuit shown above is
A$8.0 \mu\mathrm{F}$
B$6.0 \mu\mathrm{F}$
C$4.0 \mu\mathrm{F}$
D$2.0 \mu\mathrm{F}$
Correct Answer: D
The circuit has two $2 \mu\mathrm{F}$ capacitors in parallel (giving $4 \mu\mathrm{F}$) and one $4 \mu\mathrm{F}$ capacitor in series. The series combination gives $\dfrac{4 \times 4}{4 + 4} = 2 \mu\mathrm{F}$.