All 20 questions from the Post-UTME Screening (Post-UTME) Physics 2018 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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In a simple cell, a defect known as polarization is due to the
Polarization in a simple cell is caused by a layer of hydrogen bubbles building up on the copper (positive) plate, which increases internal resistance and reduces the cell's e.m.f.
A battery of e.m.f. 10V and internal resistance 2 ohm is connected to an external resistance of 3 ohm. Determine the potential drop across the 2 ohm (internal) resistance.
Current I = emf/(R+r) = 10/(3+2) = 2A. Potential drop across internal resistance = I x r = 2 x 2 = 4V.
What is the resistance of a wire 220cm long and 0.7mm in diameter at 20 degrees C? (The resistivity of the material at 20 degrees C is 3.5x10^-6 ohm.cm)
Radius = 0.035cm. Area = pi*r^2 = pi*(0.035)^2 = 0.003848 cm^2. R = (resistivity x length)/area = (3.5x10^-6 x 220)/0.003848 = 0.20 ohm.
What is the energy generated when a current of 20A flows for 30 seconds through a 50 ohm resistor?
Energy = I^2 x R x t = 20^2 x 50 x 30 = 400 x 50 x 30 = 600,000 J = 600.00 kJ.
The function of the commutator in an electric motor is to
The commutator periodically reverses the direction of current in the coil, maintaining continuous rotation of a DC motor in one direction.
In a step-up transformer, the turns ratio is 6:1. If the primary e.m.f. is 3V, find the secondary e.m.f.
Secondary emf = primary emf x turns ratio = 3 x 6 = 18V.
226-88-Ra -> X + 222-86-Rn. In the above nuclear equation, X represents
Mass number balance: 226 = A(X) + 222, so A(X)=4. Atomic number balance: 88 = Z(X) + 86, so Z(X)=2. A particle with mass number 4 and atomic number 2 is an alpha particle.
A diode valve consists of a
A diode valve is the simplest type of thermionic valve, consisting of just two electrodes: a cathode and an anode.
The escaping radiation from a modern nuclear reactor is prevented from reaching the reactor operators by
A thick concrete (and sometimes lead-lined) shield surrounding the reactor absorbs escaping radiation, protecting operators.
Which of the following is TRUE of cathode rays? I. They travel in straight lines. II. They can be deflected by electric and magnetic fields. III. They are negatively charged particles called electrons.
All three statements correctly describe cathode rays: they travel in straight lines, can be deflected by electric/magnetic fields, and are streams of electrons.
A virtual image of an object was obtained at a distance of 30.0 cm from a converging lens of focal length 20.0cm. What is the distance of the object from the lens?
For a virtual image, v=-30cm, f=20cm. Using 1/v-1/u=1/f: -1/30-1/u=1/20, giving u=-12cm, so object distance is 12.0cm.
Use the diagram above (a converging lens with 2F', F', F and 2F marked) to answer this question. Where must an object be placed so that an inverted but enlarged image can be formed?
An object placed between F and 2F (on the object side, F' and 2F') produces a real, inverted, magnified image beyond 2F on the other side.
The image formed by the objective lens of a compound microscope is usually
The objective lens of a compound microscope forms a real, inverted, magnified image, which is then further magnified by the eyepiece.
The closest point at which an object placed in front of the eye could be clearly seen is called the
The near point is the closest distance at which the eye can focus clearly on an object.
Use the figure above (three overlapping circles labelled RED, GREEN and BLUE, with the central overlap region labelled H) to answer this question. In the figure above, what is the colour of the region of intersection of the red, green and blue circles labelled H?
The overlap of all three primary colours of light (red, green and blue) produces white light.
A sheet of white paper viewed through red glass appears red because
The red glass filter transmits only red light and absorbs other wavelengths, so the white paper (reflecting all colours) appears red through it.
Which of the following statements about a charged electroscope are correct? I. when a negatively charged object is brought close to a negatively charged electroscope, the divergence increases. II. When a positively charged object is brought close to a negatively charged electroscope, the divergence decreases. III. When an uncharged object is brought close to a negatively charged electroscope, the divergence decreases.
Bringing a like (negative) charge closer increases divergence (repulsion); bringing an opposite (positive) charge closer decreases divergence; an uncharged object has negligible direct effect (statement III is not generally correct).
The ground state of an atom occurs when the electrons are
The ground state is the lowest possible energy configuration of an atom's electrons.
A neutral point in a magnetic field is defined as a point where the
A neutral point is where the resultant magnetic flux density (from all sources, including the earth's field) is zero.
The angle between the magnetic and geographic meridian is the angle of
The angle between magnetic north and true (geographic) north is called the angle of declination.
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