These particle-to-particle, mechanical vibrations of sound conductance qualify sound waves as mechanical waves. Sound energy, or energy associated with the vibrations created by a vibrating source, requires a medium to travel, which makes sound energy a mechanical wave.

The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light. In miles per hour, light speed is, well, a lot: about 670,616,629 mph. If you could travel at the speed of light, you could go around the Earth 7.5 times in one second.

What eventually happens to a sound wave traveling through the air? The energy of the sound wave is eventually dissipated into heat. Since this pressure wave is present as long as the plane is moving faster than the speed of sound, the aircraft continually makes a sonic boom.

When two waves meet at a point, they interfere with each other. There are two types of interference, constructive and destructive. In constructive interference, the amplitudes of the two waves add together resulting in a higher wave at the point they meet.

Like other waves, light waves can travel through matter, but light waves are different from water waves and sound waves. In empty space, light travels at a speed of about 300,000 km/s. Light travels so fast that light emitted from the Sun travels 150 million km to Earth in only about eight and a half minutes.

The refraction of light at the surface of water makes ponds and swimming pools appear shallower than they really are. If you look at a stick that is poking into some water at an angle the stick looks bent because of refraction. The bottom of the stick seems to be nearer the surface of the water than it really is.

Since air has an index of refraction of essentially 1 and water has an index of refraction of 1.33 the angle from which the rays of light reach your eyes is larger than the angle they would in air. This makes the angular size larger to your eyes which makes the object look larger relative to how they would look in air.

When the light ray from water reaches our eye, the eye traces them back as straight lines (shown as dashed lines) which intersect at a higher position than where the actual rays originated. This cause the depth to appear higher and we cannot see the actual depth of the lake.

Apparent depth of pond is less than real depth of pond due to the refraction of light. When rays travel from denser medium to rare medium it bends away from the normal and the actual depth appear to be raised.

A ray of light will bend towards the normal when crossing the boundary from a medium in which it travels fast into a medium in which it travels slowly.

Total internal reflection, in physics, complete reflection of a ray of light within a medium such as water or glass from the surrounding surfaces back into the medium. The phenomenon occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle.

Two Requirements for Total Internal Reflection the light is in the more dense medium and approaching the less dense medium. the angle of incidence is greater than the so-called critical angle.

If the angle of incidence is bigger than the critical angle, the refracted ray will not emerge from the medium, but will be reflected back into the medium. This is called total internal reflection. The critical angle occurs when the angle of incidence where the angle of refraction is 90°.

The phenomenon of total internal reflection of light is used in many optical instruments like telescopes, microscopes, binoculars, spectroscopes, periscopes etc. The brilliance of a diamond is due to total internal reflection. Optical fibre works on the principle of total internal reflection.