Wave Reflection and Superposition

Changing Medium Densities

• When pulses arrive at a more dense medium, the speed is reduced
• When a pulse arrives at a less dense medium, the speed is increased
• In both cases, a small amount of energy is reflected, and therefore the transmitted amplitude is less

Frequency at Boundaries

• When waves move from one medium to another their velocity changes.
• Waves travel more slowly in dense mediums, and faster in less dense mediums.
• Wavelength is compressed in dense mediums, and expanded in less dense mediums.
• Frequency is constant across mediums because for frequency to change would mean the colour of light would change

\[ \begin{aligned} f_{thick} &= f_{thin} && \text{Substitute $v=f\lambda$} \newline \frac{v_{thick}}{\lambda_{thick}} &= \frac{v_{thin}}{\lambda_{thin}} \end{aligned} \]

Task / Ngohe

1. Collect a sheet.
2. Use your notes to help you write a paragraph to describe each wave situation.

Whakatika Tahi

As the wave impacts the wall its energy is reflected. Because the wall is a fixed point, the wave is inverted. In this case, we can see that no energy is lost (ideal world) because the amplitude has not changed. As it is travelling in the same medium the speed is the same, and given a constant frequency, the wavelength is also the same.

Whakatika Rua

As the incident pulse encounters the change in medium most of the energy is transmitted, but some is reflected. This reflected pulse is not inverted. The transmitted pulse therefore has less energy and less amplitude. In the less dense medium it travels faster, but due to constant frequency it must have a longer wavelength which we can see.

Frequency and Sound

• The frequency of a sound wave determines the pitch that you hear
• A low frequency is a low pitch (low note)
• A high frequency is a high pitch (high note)

https://www.onlinetonegenerator.com/hearingtest.html

Task/Ngohe

Homework Booklet Q6!