Physics MCQs

Notes:
The speed of sound varies depending on the temperature, pressure, and density of the medium through which the sound waves travel. In most of the cases, it is density which matters. Sound travels faster through denser air (or other material). The density of air is affected by atmospheric pressure, temperature, and altitude.

Notes:
The key to why clouds float is that the density of the same volume of cloud material is less than the density of the same amount of dry air. Just as oil floats on water because it is less dense, clouds float on air because the moist air in clouds is comparatively less denser than dry air.

Notes:
Real gases approximate ideal gases when their pressure is relatively low, and their temperature is reasonably high. A real gas deviates increasingly from ideality as it is compressed and cooled to near the point at which it will condense into a liquid. Compressing forces the molecules closer together so that intermolecular forces become stronger, and cooling reduces the kinetic energy of the molecules, so that they are more easily held by these forces.

Notes:
Clothing flammability is the speed at which clothes catch fire. Cotton and linen generally burn more easily because of their light texture. Besides, since they do not melt or shrink away from open flame, they have a rapid rate of combustion. Synthetic fibres such as nylon does not catch fire readily; however, they melt and stick to skin after catching fire.

Notes:
Friction between two surfaces can be reduced by polishing them. The interlocking and projections are minimized by this method. Friction can also be reduced by applying lubricants between the contact surfaces to fill the fine pores or depressions in the surfaces and make them smooth. Friction does not depend on the area of contact.

Notes:
Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet lens because of their compensating optical properties, which reduces chromatic aberration (colour defects).

Notes:
For a hyper-metropic eye ,the near points shift away from the eye i. e. farther away from the normal near point (25cm). In a hypermetropic eye, the light is not bent sufficiently so that it focuses at a point behind the retina. Here a person sees well for distance but near vision is difficult and causes strain. Hence, hypermetropic people are called long-sighted. To correct the hypermetropic eye, a plus lens (convex lens) is used to focus image on retina.

Notes:
Concave mirrors are used as dental mirrors. This is because concave mirrors produce highly magnified images which are useful in obtaining larger view of teeth and gums. These mirrors enable the dentists to see the minute details of the tooth in a magnified form.

Notes:
In theory, 2 satellites in diametrically opposite geosynchronous orbits could cover the planet. In order for the satellites to communicate, a minimum of 3 would be needed, each at a 60 degree angle to the others. At this point, the strength and quality of coverage increases proportionally to the number of satellites.

Notes:
In United States, an oil barrel is defined as 42 US gallons, which is about 159 litres or 35 imperial gallons.