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.

Clay is a highly plastic substance. Clay particles are attracted to each other by weak electrostatic forces. Water conducts these forces. Thus, dry clay mixed with a fifth of its weight in water, becomes the plastic material clay artists use.

Sonar is a device that uses sound waves to detect and range objects on or under the surface of the water.

When a bar magnet is cut perpendicular to its length then the pole strength of each piece remains the same (but the magnetic moment is halved). If a magnet is cut parallel to its length then the pole strength of the pieces becomes half.

The function of ball bearings in a wheel is to convert kinetic friction into rolling friction because rolling friction is much lesser than sliding friction. Ball bearings reduce friction and facilitate easy movement.

Aluminium and its alloys are used for making aircraft and rockets, due to their high strength at relatively low density.

Pycnometers are used for measuring and comparing densities or specific gravities of liquids and solids, including soil.

Asteroids are rocky objects revolving around the sun that are too small to be called planets. The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Mars and Jupiter.

Among the given materials sound travels fastest in steel. Sound travels fastest through solids. This is because molecules in a solid medium are much closer together than those in a liquid or gas, allowing sound waves to travel more quickly through it. Sound cannot travel in a vacuum as there is no medium.

The centre of gravity of a sprinter during the race lies ahead of his feet. It is an imaginary point in a body of matter where the total weight of the body may be thought to be concentrated. Running with a lean allows gravity to pull the runner forward.