Physics Questions and Answers

Answer: C

It depends on both the nature of the signal and the nature of the medium.

The signal's frequency and power determine how far it can carry and how much information it holds, while the medium fixes the attenuation, dispersion and noise it will meet. Neither alone decides the quality of transmission.

Answer: C

On the Kelvin scale ice melts at 273 K.

\[T(\mathrm{K}) = t(^\circ\mathrm{C}) + 273.15\] so 0 °C is 273.15 K, usually rounded to 273. A kelvin is the same size as a degree Celsius; only the zero differs, absolute zero being \(-273.15\) °C.

Answer: B

It will weigh 2 N.

Weight is \(W = mg\), and the mass is unchanged, so the weight falls in the same proportion as \(g\): \[W_{moon} = \frac{12}{6} = 2\ \mathrm{N}\] The mass remains \(12/9.8 \approx 1.22\) kg on both bodies.

Answer: D

Because mercury is denser than steel.

Mercury's density is \(13.6\ \mathrm{g\,cm^{-3}}\) against steel's 7.8, so the ball displaces its own weight of mercury while still less than half submerged, and it floats by Archimedes' principle. Surface tension helps a little but is not the reason.

Answer: C

Heat flows according to the temperatures of the two objects.

It always passes from the hotter to the colder body, whatever their masses or heat contents, until both reach the same temperature. This is the content of the second law of thermodynamics, and the reason the zeroth law makes temperature meaningful.

Answer: B

The red ray is deviated least.

Deviation depends on refractive index, and \(n\) falls as wavelength rises - Cauchy's relation. Red has the longest visible wavelength, so glass bends it least; violet, at the short end, is bent most. That difference in deviation is dispersion, and is what spreads the light into a spectrum.

Answer: B

The train is moving forward and gaining speed.

While in the air the coin keeps the horizontal velocity it had when tossed. If the train accelerates in that interval, it moves further than the coin does, so the coin lands behind the point from which it was thrown.

Answer: C

The level will remain the same.

Floating ice displaces its own weight of water; on melting it becomes exactly that weight of water, which occupies exactly the volume it had been displacing. This is why melting sea ice does not raise sea level, whereas melting land ice does.

Answer: C

The unit of solid angle is the steradian.

One steradian subtends an area \(r^2\) on a sphere of radius \(r\), so a whole sphere is \(4\pi\) steradians. The radian is the corresponding unit for plane angle.

Answer: A

Because the harmonium uses a tempered scale.

Its reeds are tuned to fixed, equally spaced semitones, so the intervals are slight compromises. Indian classical music uses just intonation with microtonal shrutis and continuous glides between notes - neither of which a fixed-pitch reed instrument can follow, which is why the sarangi and now the violin are preferred.