Reflection of waves

Waves - including sound and light - can be reflected at the boundary between two
different materials. The reflection of sound causes echoes.
The law of reflection states that:
angle of incidence = angle of reflection
For example, if a light ray hits a surface at 32°, it will be reflected at 32°.
The angles of incidence and reflection are measured between the light ray and
the normal - an imaginary line at 90° to the surface. The diagrams show a water wave
being reflected at a barrier, and a light ray being reflected at a plane mirror.

Specular reflection
Reflection from a smooth, flat surface is called specular reflection. This is the type of
reflection that happens with a flat mirror. The image in a mirror is:

 upright
 virtual

In a virtual image, the rays appear to diverge from behind the mirror, so the image
appears to come from behind the mirror.
Figure caption,
A ray diagram showing how an image forms in a plane mirror
Diffuse reflection
If a surface is rough, diffuse reflection happens. Instead of forming an image, the
reflected light is scattered in all directions. This may cause a distorted image of the
object, as occurs with rippling water, or no image at all. Each individual reflection still
obeys the law of reflection, but the different parts of the rough surface are at different
angles.
Reflection vs. Refraction: What’s the Difference?

Refraction and reflection are characteristics of light that often confuse people. Reflection
happens when light bounces off an object, and refraction occurs when light passes
through an object.

Light consists of tiny particles called photons. When photons bounce off an object, they
reflect the light. That’s why you can see your reflection in a mirror. Likewise, when
photons pass through an object, they refract the light.

The guide below explains the difference between both phenomena. We also describe
the applications of reflection and refraction in our everyday lives.
Overview of Reflection

Image

Credit: 12019, Pixabay

When light waves bounce off a surface, we see a reflection. The angle between the light
that hits the surface, and the angle of the reflected light waves determine how much
reflected light we see.

The amount of reflected light also depends on the nature of the reflecting surface. For
example, a smooth, shiny surface reflects more light than a dull, rougher surface.

Mirrors reflect light in a straight line. So, we see a clear image. When light waves hit a
curved surface, they bounce off at different angles. The waves reflecting off the curved
surface interfere with each other, producing a distorted image.

Light waves reflecting off a surface can produce specific effects. When light reflects off
a concave surface, it forms a real image. A convex surface forms a virtual image.

Examples of Reflection
The most common example of reflection is a mirror. However, you must have noticed
that a mirror shows a left-right reversal of the image.
It happens because light waves change direction when they bounce off a mirror. The
angle between the incoming and reflected light waves is the same.

Another typical example of reflection is the surface of a still pond or lake. When light
reflects off the smooth surface of the water, it produces a clear image. Similarly, you
can also see your reflection on your phone’s screen.

Types of Reflection
There are three types of reflection of light. They differ based on the type of object and
angles created by the light.

Diffuse Reflection

In diffuse reflection, the light that hits an object is scattered in many directions. It
happens when the surface is not smooth.

The light waves hit the rough surface and bounce off in different directions. Diffuse
reflection is responsible for the image we see in a mirror.
Image

Credit: Dannie Jing, Unsplash

Specular Reflection

Specular surfaces are smooth and shiny, like a mirror. The light waves bounce off these
surfaces at a definite angle.

The angle between the surface and the reflected ray equals the angle between the
surface and the incident ray. Specular reflection has applications in lasers, telescopes,
and periscopes.

Glossy Reflection

Glossy surfaces are a type of specular surface, except that they have micro surfaces at
an angle to the plane of the surface. The micro surfaces scatter the light in many
directions.

It results in a reflection that is not as sharp as specular reflection. We see glossy

reflections in car paint and accessories.
Overview of Refraction
Image Credit: Billion Photos, Shutterstock

Refraction occurs when waves travel through a medium and bend due to a change in
their speed. The change in speed can be due to the waves traveling from one medium
to another or the waves traveling through a medium with different properties in different
regions.

The amount of bending depends on the difference in the speed of the waves in the two
regions. For instance, when light waves travel from air into water, they are bent toward
the normal (the line perpendicular to the surface where the incidence strikes) because
the speed of light is slower in water than in air.
The amount of bending also depends on the refractive index. The refractive index is the
ratio of the speed of waves in a vacuum to the speed of waves in a medium. For
example, water’s refractive index is 1.33. Meanwhile, the air’s refractive index is 1.00.
Therefore, when light enters a medium with a higher refractive index (air to water), it
slows down. Thus, it bends towards the normal line. When light travels from a medium
with a lower refractive index to one with a higher refractive index, it bends away from
the normal.

Examples of Refraction
Refraction occurs in many everyday situations. The most notable example is the human
eye. The human eye uses refraction to allow us to see. When light enters the eye,
refraction occurs in the cornea. The cornea is the clear, curved front surface of the eye.
It has a higher refractive index than the air, so it bends the light waves as they enter the
eye.

Then, the lens, a clear, curved structure behind the cornea, refracts the light. Finally, it
further bends the light so that it focuses on the retina.

You can also notice refraction when you are swimming. For example, when you look at
the bottom of a pool, it may appear closer than it is. You have this illusion because the
water bends the light waves, making the bottom of the pool appear closer than it is in
reality.

This same principle applies to other objects that are submerged in water. For example,
a straw in a glass of water appears bent because the light waves are bent as they travel
from the air to the water.

Another notable example of refraction is rainbow formation. When light hits water
droplets, it is bent and refracted. Each wavelength bends at a different angle. That’s
why you see seven colors of the rainbow.

Types of Refraction
The types of refraction depend on the density of the media. Here are the two standard
types.
Mirrors are present on the back of the meter. When the user looks into the mirror, they
see the reading at eye level. The user can take an accurate reading without worrying
about the parallax error.