Physics Quiz 6

A parabolic concave mirror is used in torches and car headlamps as reflectors. This type of mirror is capable of directing the light at a particular point as they have converging power. These mirrors provide clear visibility.

If the force is held constant the pressure is inversely proportional to the area (Pressure = force/area). Here area of the nail is much greater than the area of the needle. Thus, needle exerts more pressure than nail on the balloon.

The velocity of sound in the air does not change with the change of Pressure of gas (air). The speed of sound increases with the increase of the temperature of the medium.

The apparent weight of a man in a lift is less than the real weight when the lift is going down with an acceleration. When a lift accelerates upwards, the apparent weight of the person inside it increases; and when a lift accelerates downwards, the apparent weight of the person inside it decreases.

A mirage occurs because of total internal reflection by layers of air. When the ground is very hot and the air is cool, the hot ground warms a layer of air just above the ground. When the light moves through the cold air and into the layer of hot air it is refracted (bent). A layer of very warm air near the ground refracts the light from the sky nearly into a U-shaped bend.

Electrostatic precipitator is used to control the pollution of air. It is a filterless device that removes fine particles, like dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit.

A simple microscope is a magnifying glass that has a single or double convex lens with a short focal length.

Interference may be defined as waves emerging from two different sources, producing different wave-fronts. It is demonstrated by the light reflected from a film of oil floating on water. Another example is the thin film of a soap bubble, which reflects a spectrum of beautiful colours when illuminated by natural or artificial light sources.

When a ship enters the sea from a river it rises a little because seawater has more density than river water. Due to the higher density of seawater, the upthrust produced by the seawater on the ship is greater as compared to that produced by river water.

The most common material used for the heating element is Nichrome. Nichrome is the alloy of the Nickel and chromium; in this alloy, the nickel is 80% and the chromium is 20%. It is corrosion-resistant and has a high melting point of about 1400 degree C.