All 20 questions from the Post-UTME Screening (Post-UTME) Physics 2016 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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When the volume of a gas in an enclosure is decreased at constant temperature, the gas molecules
Reducing the volume at constant temperature packs molecules closer, increasing the frequency of collisions.
A vertical wire of length 2m and tensile stress 6.08 x 10^7Nm-2 fixed at its upper end carries a 3kg mass at the other end. If the wire extends by 0.8mm, calculate its Young's modulus.
Strain = extension/length = 0.8x10^-3/2 = 4x10^-4. Young's modulus = stress/strain = 6.08x10^7/4x10^-4 = 1.52x10^11 Nm-2.
According to the kinetic theory of matter, when temperature increases, molecules of solids will
Increased temperature gives molecules more kinetic energy, causing them to vibrate faster and occupy a slightly larger space (thermal expansion).
The amount of heat needed to vapourize 0.5kg of water at its boiling point is the same in quantity as the heat of
The latent heat of vaporization equals (in magnitude) the latent heat released during condensation of the same mass.
A 9m steel bar is heated through 20C. What is the change in its length? [alpha steel = 1.2 x 10-5K-1]
Change in length = L x alpha x deltaT = 9 x 1.2x10^-5 x 20 = 2.16x10^-3 m = 2.16mm.
How long will it take a 1000W heater to raise the temperature of 0.5kg of water from 15C to 95C? [Specific heat capacity of water = 4200Jkg-1K-1]
Heat needed = mcdeltaT = 0.5 x 4200 x 80 = 168000J. Time = Q/P = 168000/1000 = 168.0s.
Radiation from the sun is able to reach us on the earth because radiant energy
Radiant energy (electromagnetic radiation) can travel through a vacuum, unlike sound or convection, allowing it to reach earth from the sun.
A solid weigh 0.21N in air and 0.19N when fully immersed in water. Calculate its relative density.
Relative density = weight in air/(weight in air - weight in water) = 0.21/(0.21-0.19) = 0.21/0.02 = 10.50.
An A.C voltage has a peak value of 170V. What is the instantaneous voltage when it reaches 45 degrees of its cycle?
V = Vpeak x sin(45) = 170 x 0.707 = 120V.
226Ra ---> 4He + 222Rn. In the equation above, the change in mass number by the conversion of radium into radon is
Mass number changes from 226 to 222, a change of 4, matching the mass number of the emitted alpha particle (4He).
A bullet is fired from a point P with an initial velocity of 50 ms-1 at an angle of 45 degrees to the horizontal. At what distance from the point P will the bullet hit the ground assuming that the ground is horizontal throughout the trajectory. (Take g = 10ms-2)
Range = v^2.sin(2theta)/g = 50^2 x sin(90)/10 = 2500/10 = 250m.
Calculate the force on an electron situated in a uniform electric field of intensity 120 000Vm-1
F = qE = 1.6x10^-19 x 120000 = 1.92x10^-14N.
A current of 5A flowing in a circuit falls to zero in 0.1 sec. If the average e.m.f of 200V is induced, what is the self-inductance of the circuit?
emf = L(dI/dt). L = emf/(dI/dt) = 200/(5/0.1) = 200/50 = 4H.
Use the diagram above (an AC circuit with 120V, 60/pi Hz supply, a resistor R and capacitor C = 30uF) to answer this question. In the circuit above, calculate the reactance of the capacitor.
Xc = 1/(2.pi.f.C) = 1/(2 x 60 x 30x10^-6) = 277.78 ohm (using f=60/pi so that 2.pi.f=120).
A step-down transformer reduces the voltage from 2400V to 120V. If the primary winding has 4000 turns, determine the number of turns in the secondary winding.
Ns = Np x Vs/Vp = 4000 x 120/2400 = 200 turns.
I. Travel in straight lines II. Have kinetic energy III. produce heat on collision with metals IV. Can be deflected by a magnetic field. From the above, which of the combinations is a characteristic of cathode rays?
Cathode rays travel in straight lines, possess kinetic energy, produce heat on collision, and can be deflected by magnetic fields - all four properties apply.
A coil having an inductance of 0.14H and a resistance of 12 ohm is connected across a 110V, 25Hz line. Determine the current in the coil.
XL=2.pi.f.L=2x3.14x25x0.14=22 ohm. Z=sqrt(R^2+XL^2)=sqrt(144+484)=25.06 ohm. I=V/Z=110/25.06=4.4A.
What is the time required to electroplate 3.00g of silver onto a brass casting by using a steady current of 15.0A? [e.c.e. of silver = 0.001118gC-1]
t = mass/(e.c.e. x I) = 3.00/(0.001118x15) = 178.89s.
The electron diffraction experiment illustrates
Electron diffraction demonstrates that particles (electrons) exhibit wave-like properties.
An induced e.m.f. is obtained between the ends of a horizontal steel axle of a moving train because the
The vertical component of the earth's magnetic field, combined with the horizontal motion of the conducting axle, induces an emf across it.
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