Reflection of Waves

Introduction

The shift in direction of a wave as it strikes the interface between two materials is known as reflection. The bouncing back of a wave when it strikes an interface between two mediums is known as a reflection of waves. When a wave collides with a surface, a portion of the wave is reflected while the rest is transmitted into the second medium. The transmitted wave can also be referred to as a refracted wave if the wave is incident obliquely on the boundary. The incident and refracted waves are subject to Snell’s Law of Refraction, whereas the incident and reflected waves are subject to the rules of reflection. A wave or a pulse can be reflected from one of two surfaces: a fixed wall or a ring.

Types of reflection of waves

Depending on the medium, reflection of waves can be categorised into 2 types- Free end reflection and fixed end reflection

Free-end reflection – We call it a free end when the right end of the string is connected to a ring that moves up and down on a rod without friction. When the pulse reaches the right end of the rod, the ring advances up the rod, pulling on the string and stretching it, creating a reflected pulse with the same sign and amplitude as the original pulse. The incident and reflected pulses reinforce each other in such a reflection, resulting in the maximum displacement at the end of the string: the ring’s maximum displacement is twice the amplitude of either of the pulses. As a result, there is no additional phase shift in the reflection. The reflection of a travelling wave at an open border occurs without any phase shift.

Fixed-end reflection – Consider the case of a string that is attached to a sturdy wall at its right end. When a pulse is allowed to propagate along these strings, it reaches the right end and is reflected. The pulse exerts a force on the wall when it reaches the fixed end, and the wall, according to Newton’s third law, exerts an equal and opposite force on the string. This second force causes a pulse to be generated at the support, which then travels back along the string in the opposite direction as the incident pulse. There is no displacement at the support in this type of reflection because the string is fixed there. At that time, the reflected and incident pulses have opposite signs and cancel each other out.

To summarise the two types of reflection of waves, we can state that waves are reflected appropriately at a boundary between two media. A travelling wave is reflected with a phase reversal at a stiff boundary or a closed-end, while it is reflected without a phase shift at an open boundary.

Study of reflection of waves in two-dimension

A huge glass-bottomed water tank was used to research how water ripples behave. A light shines down from above on the water, illuminating a white sheet of paper placed right below the tank. As the water goes through the tank, a portion of the light is absorbed. A water crest will absorb more light than a water trough. Wave crests are represented by the bright spots, while wave troughs are represented by the dark dots. The dark and bright areas in the ripple tank move along with the water waves.

The behaviour of the waves can be examined by examining the movement of the dark and bright spots on the sheet of paper as they hit obstacles along their course. In a Physics lesson, ripple tank demonstrations are widely used to illustrate the physics underlying wave reflection, refraction, and diffraction.

Laws of reflection

We know that, when a light is incident on a plane mirror or any reflecting surface then light gets reflected. To understand more about reflection, there are two laws of reflection.

1. First law states that incident light, reflected light and normal(Normal is defined as a perpendicular line to the mirror surface) all lie in the same plane.
2. Second law stated that incident angle and reflected angle are the same. Let consider incident light formed an angle with the normal is “i” and reflected light formed angle with the normal is “r“, so according to second law of reflection

i=r 

r ” for the angle of reflection) When a ray of light reflects off a surface, the angle of incidence equals the angle of reflection, according to the law of reflection.