At what temperature (in Fahrenheit) pure water freezes?
Answer: C
Pure water freezes at 32 °F.
\[F = \frac{9}{5}C + 32 = \frac{9}{5}(0) + 32 = 32\] Fahrenheit set zero at the temperature of a brine mixture, which is why the freezing point of water falls at 32 rather than at 0 on his scale.
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Which of the following is not a transverse wave?
Answer: C
Sound waves are not transverse.
Sound in air is longitudinal: the molecules oscillate along the direction of travel, producing compressions and rarefactions. Light and radio waves are electromagnetic, with electric and magnetic fields oscillating at right angles to the direction of propagation. This is why sound cannot be polarised but light can.
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A woman’s voice is shriller than a man’s voice due to
Answer: C
Because of the higher frequency of a woman's voice.
Pitch is determined by frequency. Women's vocal cords are shorter and thinner, so they vibrate faster - typically 165–255 Hz against 85–180 Hz for men. Amplitude governs loudness, not shrillness.
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Lightning heats the surrounding air to
Answer: C
Lightning heats the air to about 30,000 °C.
That is roughly five times the temperature of the sun's surface. The air expands explosively at that heat, and the shock wave it sends out is what we hear as thunder.
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Two metallic plates of equal thickness, with coefficients of thermal conductivity K1 and K2, are placed together face to face to form a composite plate. What is the equivalent conductivity?
Answer: B
The equivalent conductivity is \(2K_1K_2/(K_1+K_2)\).
Plates in series pass the same heat current, so their thermal resistances add: \[\frac{2d}{K_{eq}} = \frac{d}{K_1} + \frac{d}{K_2}\]
\[\frac{2}{K_{eq}} = \frac{K_1+K_2}{K_1K_2} \Rightarrow K_{eq} = \frac{2K_1K_2}{K_1+K_2}\]
This is the harmonic mean of the two conductivities.
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Which part of the flame is the hottest?
Answer: A
The blue zone is the hottest part of the flame.
There the air supply is plentiful and combustion is complete, so the temperature reaches about 1,500 °C. The luminous yellow region is cooler, its light coming from glowing unburnt carbon, and the innermost dark zone is unburnt gas and coldest of all.
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Which statement best describes an igneous intrusion?
Answer: B
An igneous intrusion is formed when magma is injected into the surrounding rock.
The magma cools slowly underground, insulated by the country rock, so large crystals have time to grow - which is why intrusive rock such as granite is coarse-grained, while lava cooling at the surface gives fine-grained basalt.
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Which of the following uses a Non Renewable Energy Source?
Answer: C
A nuclear power plant uses a non-renewable source.
Uranium ore is a finite mineral resource. Wind, hydroelectric and tidal plants all draw on flows driven continuously by the sun and the moon, and are not depleted by use.
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The capacity of a communication channel is measured in
Answer: B
Channel capacity is measured by its bandwidth.
Bandwidth is the range of frequencies the channel can carry, and by the Shannon-Hartley theorem the maximum data rate is \[C = B\log_2\!\left(1 + \frac{S}{N}\right)\] so capacity rises directly with bandwidth. Baud rate counts signal changes per second, which is a different thing.
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Fog is an example of a
Answer: A
Fog is a liquid dispersed in a gas.
It is an aerosol of tiny water droplets suspended in air, formed when moist air is cooled below its dew point. Smoke is a solid in a gas, an emulsion a liquid in a liquid, and foam a gas in a liquid.
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