Reflection and Transmission of Waves

Our Objective

To demonstrate reflection and transmission of waves at the boundary of two media.

The Theory

Reflection of wave or pulse at rigid boundary

When a pulse or wave travels through medium if the boundary is rigid, pulse reflects. Displacement of particle at fixed end is 0. So, pulse suffers a phase change of 180° on reflection. The pulse gets inverted after reflection at rigid boundary. It has the same speed, amplitude and wavelength after reflection.

Fig : Reflection of a pulse meeting a rigid boundary

Reflection of a wave or pulse when boundary is free

If the rope is loosely connected to a pole, the boundary is free to move. When we give pulse to rope pulse reflects without inversion. Reflected waves have the same speed, amplitude and wavelength.

Fig: Reflection of a pulse meeting a free end

When a wave or pulse travels from rarer medium to denser medium

A slinky is attached to heavier spring. When we give a pulse to the slinky, a portion of energy gets transmitted to heavier spring and a portion of energy get reflected to the slinky.

The mass of the heavier spring is greater than a slinky.  When the pulse goes from the slinky to heavier spring amplitude of the pulse at the heavier spring decreases and speed of the pulse at heavier spring will be less. The wavelength of the transmitted pulse will be less.

Reflected pulse on slinky will be inverted. The speed and wavelength of reflected pulse will be the same as the incident wave.

Fig: Reflection and transmission of a pulse moving from a rarer medium to a denser medium

When a wave or pulse travels from denser medium to rarer medium

A slinky is attached to heavier spring. When we give a pulse to the heavier spring, a portion of energy gets transmitted to slinky, and a portion of energy gets reflected to the heavy spring.

The mass of the slinky is lesser than a heavier spring.  When pulse goes from heavier spring to slinky the speed of the pulse at slinky will be high. The wavelength of transmitted pulse will be high.

Reflected pulse will not be inverted. The speed and wavelength of reflected pulse will be same as incident wave.

Fig: Reflection and transmission of a pulse moving from a denser medium to a rarer medium

Learning Outcomes

• Students can understand how a pulse reflects at a rigid boundary.
• Students can understand how a pulse reflects at a free end.
• Students can understand what happens to pulse when it passes through rarer medium to denser medium or vice versa.