What is the difference between transmission and reflection at a boundary?

Reflection occurs when a wave bounces off a boundary and stays in the original medium, while transmission occurs when the wave passes through the boundary into the second medium. The ratio of reflection to transmission depends on the density difference between the two media.

How does the density of two media affect wave behavior at their interface?

If the densities are similar, most of the wave energy is transmitted into the second medium. If the densities are significantly different, most of the energy is reflected back into the first medium.

Why is a gel used between the transducer and the skin during an ultrasound scan?

The gel has a density similar to skin, which eliminates the air gap. Since air and skin have very different densities, an air gap would reflect most of the ultrasound before it could enter the body; the gel ensures maximum transmission.

What is the most common mistake when calculating the depth of an object using sonar?

The most common mistake is forgetting to divide the total travel time by two. Because the pulse travels to the object and the echo travels back, the time recorded represents twice the distance to the target.

Why can't a transducer transmit and receive a signal at the exact same time?

Transducers typically use the same component to both emit pulses and detect echoes. If the pulse duration is too long, the outgoing wave will interfere with or mask the incoming reflected wave, leading to data loss.

What happens to the resolution of a pulse-echo image if the wavelength is increased?

The resolution decreases (gets worse). Longer wavelengths diffract more around small objects, making it difficult to distinguish fine details; therefore, shorter wavelengths are preferred for high-resolution imaging.

Define the 'Interface' in the context of wave behavior.

The interface is the boundary or surface where two different media meet. It is the specific location where reflection, transmission, and refraction of waves occur.

What is a 'Transducer'?

A transducer is a device that converts energy from one form to another. In pulse-echo systems, it converts electrical energy into wave pulses (like ultrasound) and then converts the returning reflected waves back into electrical signals.

State the Law of Reflection.

The Law of Reflection states that the angle of incidence is equal to the angle of reflection ($ \theta_i = \theta_r $), where both angles are measured relative to the normal line perpendicular to the surface.

What is the formula for calculating depth in a pulse-echo system?

The formula is $ d = \frac{v \cdot t}{2} $, where $ d $ is the depth, $ v $ is the speed of the wave in the medium, and $ t $ is the total time taken for the pulse to go and the echo to return.

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5. Waves & Particle Nature of Light

Transmission & Reflection of Waves

Summary

The behavior of waves at the boundary between two media is governed by the principles of transmission and reflection. When a wave encounters an interface, its energy is partitioned based on the physical properties (such as density) of the media, enabling technologies like ultrasound and sonar to map internal or underwater structures through pulse-echo techniques.

1. Definition & Core Concepts

Interface (Boundary): The physical surface where two different media meet, such as the boundary between air and glass or skin and muscle.
Reflection: The process where a wave strikes a boundary and is redirected back into the original medium rather than passing through.
Transmission: The process where a wave passes through the boundary and continues into the second medium, often with a change in speed or direction.
Incident Wave: The original wave traveling toward the boundary before any interaction occurs.

Diagram showing an incident wave hitting a boundary, splitting into a reflected wave and a transmitted wave.

2. Underlying Principles

Law of Reflection: For any reflected wave, the angle of incidence (measured from the normal) is exactly equal to the angle of reflection ( $\theta_i = \theta_r$ ).
Energy Partitioning: The amount of energy reflected versus transmitted depends on the difference in acoustic impedance (often related to density) between the two media.
Density Matching: When two media have very similar densities, most of the wave energy is transmitted; when they have significantly different densities, most energy is reflected.
Absorption: As a wave travels through a medium, some of its energy is converted into other forms (like heat), leading to a decrease in amplitude over distance.

3. Methods & Techniques: Pulse-Echo

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions