Electronegativity is a measure of
Answer: B
Electronegativity is a measure of non-metallic character.
It is the tendency of an atom to attract a shared pair of electrons towards itself, and it rises across a period and falls down a group - exactly the trend of non-metallic character. Metals are electropositive, giving electrons up rather than attracting them.
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The velocity required to place a vehicle in orbit round the moon is _______ that required to place it in orbit round the earth
Answer: A
The velocity needed is less than that for an earth orbit.
Orbital velocity is \[v = \sqrt{\frac{GM}{R}}\] and the moon's mass is about 1/81 of the earth's while its radius is about 1/3.7, so \(v\) works out at roughly \(1.7\ \mathrm{km\,s^{-1}}\) against \(7.9\) for the earth - a little over a fifth.
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When one enters a dark room after being in bright light one is not able to see anything clearly for a while because
Answer: C
The iris cannot dilate the pupil quickly enough.
In bright light the pupil is constricted to a small aperture; on entering darkness the iris muscles need time to open it, and the retinal pigment rhodopsin, bleached by the bright light, takes several minutes to regenerate. Full dark adaptation takes about twenty to thirty minutes.
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In the electrical circuit of a house, the fuse acts as
Answer: C
The fuse is a safety device.
It is a short length of wire of low melting point in series with the circuit. If the current exceeds the rated value, the heat \(I^2Rt\) melts the wire and breaks the circuit before the wiring can overheat and start a fire.
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If lift is going up with acceleration, the apparent weight of a body is
Answer: B
The apparent weight is more than the true weight.
For a lift accelerating upwards with acceleration \(a\), the floor must both support the body and accelerate it: \[N - mg = ma \Rightarrow N = m(g+a)\] The reading is that normal force, so it exceeds \(mg\). Going down with acceleration \(a\) it would read \(m(g-a)\).
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The absorption of ink by blotting paper involves:
Answer: B
Blotting paper works by capillary action.
Its loosely packed cellulose fibres leave fine pores between them. Ink wets the fibres, so adhesion exceeds cohesion and surface tension draws the liquid into the pores - the narrower the pore, the stronger the pull.
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The electrical domestic tube light gives white fluorescent light because of
Answer: D
Because ultraviolet light falls on the white coating inside the tube.
The discharge through mercury vapour emits chiefly in the ultraviolet at 254 nm, which is invisible. The phosphor coating absorbs it and re-emits in the visible range - fluorescence - which is why the tube is called fluorescent.
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Stars appears to move from east to west because
Answer: B
Because the earth rotates from west to east.
The apparent motion of the sky is the reflection of that rotation, so the stars rise in the east and set in the west just as the sun does. The whole sky appears to turn once in a sidereal day of 23 hours 56 minutes.
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It is more difficult to walk on ice than on a concrete road because
Answer: A
Because there is very little friction between ice and the feet.
Walking depends on pushing backwards against the ground and receiving a forward frictional reaction. Ice has a very low coefficient of friction, made lower still by a thin film of meltwater, so the foot slips instead of gripping.
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If a carrier wave of 1000 kHz is used to carry the signal, the length of transmitting antenna will be equal to _____ ?
Answer: A
The answer is 300 m.
The wavelength of the carrier is \[\lambda = \frac{c}{f} = \frac{3\times10^{8}}{1000\times10^{3}} = 300\ \mathrm{m}\] An antenna must be comparable to the wavelength to radiate efficiently, which is why long-wave broadcasting needs very tall masts. In practice a quarter-wave antenna of 75 m is often used.
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