All 20 questions from the Post-UTME Screening (Post-UTME) Physics 2019 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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The pressure of a given mass of gas in a closed container at a temperature of 27C is 0.1 x 10^4 Nm-2. What is the pressure of the gas when the temperature is raised to 387C?
By Gay-Lussac's law (constant volume), P2 = P1 x T2/T1 = 0.1x10^4 x 660/300, giving a pressure close to 1.29x10^4 Nm-2.
The statement 'Heat lost by the hot body equals that gained by the cold one' is assumed when determining specific heat capacity by the method of mixtures. Which of the following validates the assumption? I. Lagging the calorimeter II. Ensuring that only SI units are used. III. Weighing the calorimeter, the lid and the stirrer.
Lagging the calorimeter (to reduce heat loss to surroundings) and weighing the calorimeter/lid/stirrer (to account for their heat capacity) both help validate the no-heat-loss assumption; using SI units does not affect this physically.
A metal block of mass 5 kg was heated from 15C to 45C. If the power consumed by the heater in 5 minutes was 80W, find the specific heat capacity of the metal.
Heat supplied = P x t = 80 x 300 = 24000J. Specific heat = Q/(mxdeltaT) = 24000/(5x30) = 160 Jkg-1K-1.
During the transformation of matter from the solid to the liquid state, the heat supplied does not produce a temperature increase because
During melting (a phase change), the supplied heat (latent heat) is used entirely to break intermolecular bonds, not to raise temperature.
The essential factor that reduces heat loss by radiation in a thermos flask is the presence of
The silvered walls of a thermos flask reflect radiant heat back, reducing heat loss by radiation.
Which of the following is NOT correct about the assumptions of the kinetic theory?
Kinetic theory assumes molecules behave like perfectly ELASTIC spheres (not inelastic), so this statement is the incorrect one.
The heat from the sun reaches the earth mainly by
Heat from the sun travels through the vacuum of space and reaches earth mainly by radiation.
If the wavelength of a given light radiation is 6.0 x 10-7cm and the velocity is 3.0 x 10^8 ms-1, calculate the frequency.
Converting wavelength to metres (6x10^-9m) and using f=v/lambda = 3x10^8/6x10^-9 = 5x10^16 Hz.
The vibration in a transverse wave are
In a transverse wave, particle vibration is perpendicular to the direction the wave travels.
If the speed of sound in air is 384 ms-1, what is the wavelength of a note which is one octave higher than a note of 256 Hz?
One octave higher than 256Hz is 512Hz. Wavelength = v/f = 384/512 = 0.75m.
A pin-hole camera of magnification 10-2 is used to photograph a tree 5.0 tall. The height of the image is
Image height = magnification x object height = 10^-2 x 5.0m = 0.05m = 5.0cm.
If an object on the principal axis of a concave mirror is located between the principal focus and the centre of curvature, the image formed is
For a concave mirror with the object between F and C, the image formed is real, inverted, and magnified (larger than the object).
A pin at the bottom of a beaker filled with water appears to be at a depth of 9 cm when viewed vertically from above. If the refractive index of water is 4/3, calculate the real depth of the water in the beaker.
Real depth = apparent depth x refractive index = 9 x 4/3 = 12.00cm.
An object 2.0 cm high is placed 20cm from a converging lens of focal length 15cm. Calculate the height of the image formed.
Using 1/v = 1/f + 1/u (sign convention): 1/v = 1/15-1/20 = 1/60, so v=60cm. Magnification = 60/20 = 3. Image height = 3x2 = 6.00cm.
Which of the following radiations is associated with heat energy?
Infra-red radiation is strongly associated with heat energy.
A mixture of blue and red pigments when illuminated by white light will appear.
Mixing blue and red produces a magenta appearance.
Which of the following materials is positively charged?
Glass rubbed with silk loses electrons and becomes positively charged (a classic triboelectric example).
The armature of an electric bell is normally made of
The armature of an electric bell is made of soft iron, which is easily magnetised and demagnetised.
The rheostat can be used as
A rheostat, connected appropriately, can function as a potential divider.
Use the diagram above (a diamond/bridge arrangement of four resistors, each 100 ohm, between points P and Q) to answer this question. In the figure above, calculate the total resistance between P and Q if each of the resistors is 100 ohm
In this symmetric bridge-like network of equal resistors, the equivalent resistance between P and Q works out to 100 ohm.
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