Physics 2017 Jamb Examination
Physics 2017 Jamb Examination
Question 31
Which of the following is correct about an electric cell?
Secondary cells (like lead-acid accumulators) are designed to have a very low internal resistance. This low resistance allows them to deliver the high currents necessary for tasks like starting an engine. In contrast, primary cells (like Zinc-Carbon) generally have higher internal resistance and are prone to polarization, which limits their current output over time.
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Question 32
Which of the following is a semiconductor
Semiconductors are materials with electrical conductivity between that of a conductor (like copper or iron) and an insulator (like plastic). Silicon and Germanium are the most common elemental semiconductors used in electronics due to their four valence electrons.
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Question 33
Which of the following surfaces will absorb radiant heat energy?
Dull, black surfaces are the best absorbers and radiators of radiant heat (infrared radiation). Light-colored and shiny surfaces reflect most of the radiant energy that hits them.
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Question 34
It is known that a neutron exists in a light atomic nucleus. Which of the following also exists in the nucleus?
The nucleus of an atom consists of nucleons, which are protons and neutrons. Electrons orbit the nucleus in specific energy levels or shells.
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Question 35
The instrument to measure the relative density of liquid is
A hydrometer is an instrument used to measure the relative density (specific gravity) of liquids based on the concept of buoyancy. It consists of a weighted glass bulb that floats at different levels depending on the density of the liquid.
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Question 36
What is the speed of a body vibrating at 50 cyclic per second
The 'speed' in this context refers to angular velocity (\(\omega\)). The relationship between angular velocity and frequency (\(f\)) is:
\( \omega = 2\pi f \)
Given \( f = 50 \text{ Hz} \) (cycles per second):
\( \omega = 2 \times \pi \times 50 = 100\pi \text{ rads}^{-1} \).
\( \omega = 2\pi f \)
Given \( f = 50 \text{ Hz} \) (cycles per second):
\( \omega = 2 \times \pi \times 50 = 100\pi \text{ rads}^{-1} \).
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Question 37
The action of blotting paper on ink is due to
Capillarity (or capillary action) is the ability of a liquid to flow in narrow spaces without the assistance of external forces. Blotting paper contains many tiny pores that act like capillary tubes, drawing the ink up into the paper.
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Question 38
When two mirrors are placed at an angle of 90º to each other, how many images will be formed when an object is placed in front of the mirrors
The number of images (\(n\)) formed by two mirrors at an angle (\(\theta\)) is given by:
\( n = \frac{360}{\theta} - 1 \)
For \(\theta = 90^{\circ}\):
\( n = \frac{360}{90} - 1 = 4 - 1 = 3 \).
\( n = \frac{360}{\theta} - 1 \)
For \(\theta = 90^{\circ}\):
\( n = \frac{360}{90} - 1 = 4 - 1 = 3 \).
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Question 39
If silicon is doped with phosphorus, what type of semiconductor material will be formed?
Silicon has 4 valence electrons. Phosphorus is a pentavalent element (5 valence electrons). When silicon is doped with phosphorus, the extra electron from each phosphorus atom becomes a free charge carrier. Since the majority carriers are negative electrons, it is an n-type (negative) semiconductor.
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Question 40
Calculate the angle of minimum deviation of a 60º prism of a refractive index 1.5 [\( \sin^{-1} (0.75) = 49^{\circ} \)]
The formula for refractive index (\(n\)) in terms of the angle of the prism (\(A\)) and the angle of minimum deviation (\(D_m\)) is:
\( n = \frac{\sin((A + D_m)/2)}{\sin(A/2)} \)
Given \( n = 1.5 \) and \( A = 60^{\circ} \):
\( 1.5 = \frac{\sin((60 + D_m)/2)}{\sin(30)} \)
\( 1.5 = \frac{\sin((60 + D_m)/2)}{0.5} \)
\( 0.75 = \sin((60 + D_m)/2) \)
Using \( \sin^{-1}(0.75) = 49^{\circ} \):
\( 49 = (60 + D_m)/2 \)
\( 98 = 60 + D_m \)
\( D_m = 38^{\circ} \).
\( n = \frac{\sin((A + D_m)/2)}{\sin(A/2)} \)
Given \( n = 1.5 \) and \( A = 60^{\circ} \):
\( 1.5 = \frac{\sin((60 + D_m)/2)}{\sin(30)} \)
\( 1.5 = \frac{\sin((60 + D_m)/2)}{0.5} \)
\( 0.75 = \sin((60 + D_m)/2) \)
Using \( \sin^{-1}(0.75) = 49^{\circ} \):
\( 49 = (60 + D_m)/2 \)
\( 98 = 60 + D_m \)
\( D_m = 38^{\circ} \).