Physics 2007 Jamb Examination
Physics 2007 Jamb Examination
Question 31
The instrument that measures both a.c and d.c is?
Moving-iron instruments respond to the RMS value of flux produced by the current and therefore can indicate both alternating and direct currents (they do not rely on coil polarity). They are rugged and commonly used where both AC and DC measurements are required.
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Question 32
The phenomenon of light bending round an obstacle is?
Diffraction is the spreading or bending of waves (including light) when they encounter an obstacle or pass through an aperture comparable to their wavelength. This accounts for light appearing in the 'shadow' region behind small obstacles.
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Question 33
The instrument used by designers to obtain different colour patterns is called?
A kaleidoscope produces changing symmetrical colour patterns by internal multiple reflections of coloured pieces; it is the device designers and artists use for pattern ideas.
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Question 34
A glass plate $0.9\ \text{cm}$ thick has refractive index $1.50$. How long does it take for a pulse of light to pass through the plate? ($c=3.0\times10^{8}\ \text{ms}^{-1}$)
Thickness $d=0.9\ \text{cm}=9.0\times10^{-3}\ \text{m}$.
Speed in glass $v=\dfrac{c}{n}=\dfrac{3.0\times10^{8}}{1.50}=2.0\times10^{8}\ \text{ms}^{-1}$. $$t=\dfrac{d}{v}=\dfrac{9.0\times10^{-3}}{2.0\times10^{8}}=4.5\times10^{-11}\ \text{s}.$$ Thus the correct numerical value is $4.5\times10^{-11}\ \text{s}$.
Speed in glass $v=\dfrac{c}{n}=\dfrac{3.0\times10^{8}}{1.50}=2.0\times10^{8}\ \text{ms}^{-1}$. $$t=\dfrac{d}{v}=\dfrac{9.0\times10^{-3}}{2.0\times10^{8}}=4.5\times10^{-11}\ \text{s}.$$ Thus the correct numerical value is $4.5\times10^{-11}\ \text{s}$.
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Question 35
When an object is placed between the principal focus and the optical centre of a convex lens, it could be used as a?
Placing the object between the lens' optical centre and its principal focus produces an upright, magnified virtual image — the basic configuration of a simple (hand) microscope or magnifier.
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Question 36
The production of a pure spectrum could easily be achieved using a?
A triangular prism disperses light; with two convex lenses (one to collimate incident beam, the other to focus transmitted rays) you can produce a sharp, well-resolved pure spectrum on a screen.
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Question 37
I. Increase the melting point of the liquid.
II. Increase the boiling point of the liquid.
III. Decrease the melting point of the liquid.
IV. Decrease the boiling point of the liquid.
Which statements about the effect of increase in pressure in a liquid are correct?
II. Increase the boiling point of the liquid.
III. Decrease the melting point of the liquid.
IV. Decrease the boiling point of the liquid.
Which statements about the effect of increase in pressure in a liquid are correct?
Raising pressure on a liquid typically increases its boiling point (II is true). For substances like water, increasing pressure can lower melting point (III) — so the pair II and III are the statements commonly cited together in this context.
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Question 38
I. Mass
II. Density
III. Temperature
IV. Nature of substance
Which of the above affect diffusion?
II. Density
III. Temperature
IV. Nature of substance
Which of the above affect diffusion?
Diffusion rate depends on particle mass (lighter particles diffuse faster), the medium's density (affects mobility), and the nature of the substance (molecular size/interaction). These three (I, II, IV) are the principal factors listed here.
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Question 39
The blade of a hoe feels colder to touch in the morning than the wooden handle because the
Metals (blade) are better thermal conductors than wood (handle). When you touch the blade, it rapidly conducts heat away from your skin, producing a stronger sensation of cold compared with the wooden handle.
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Question 40
I. They should be identical
II. They should originate from the same source
III. They should be coherent
IV. They should be monochromatic
From the statements above, the conditions for two waves to interfere are?
II. They should originate from the same source
III. They should be coherent
IV. They should be monochromatic
From the statements above, the conditions for two waves to interfere are?
For stable interference you need coherence (constant phase relationship) and monochromaticity (single frequency). Identical waveforms help (same amplitude/shape) — so the commonly listed minimal set here is I, III and IV.