All of WAVES in 15 mins - AS & A-level Physics

Summary

This comprehensive script covers various wave phenomena, including longitudinal and transverse waves, wave properties like amplitude, frequency, and wavelength, and the wave equation. It also explains refraction, Snell's law, total internal reflection, and the use of optical fibers. The script delves into lens behavior, polarization, and the formation of stationary waves, including harmonics and diffraction patterns. It also discusses Thomas Young's double-slit experiment and diffraction with gratings, offering insights into light behavior and interference patterns. A thorough exploration of wave dynamics and their applications in optics and fiber optics is provided.

Takeaways

• 😀 Longitudinal waves have oscillations parallel to the energy transfer direction, with compressions and rarefactions as key features.
• 😀 Transverse waves have oscillations perpendicular to the energy transfer direction, and their waveforms are characterized by displacement.
• 😀 The amplitude of a wave is the maximum displacement from equilibrium, and the wavelength (Lambda) represents the distance for one complete wave cycle.
• 😀 The time period of a wave is the time for one full wave to pass, while frequency (f) is the number of waves passing a point per second. They are related by f = 1/t.
• 😀 The wave equation, V = f * Lambda, relates wave speed (V) to frequency and wavelength.
• 😀 Light waves refract when passing through different media, with the refractive index (n) determining how much the wave slows down and changes direction.
• 😀 Snell's law describes refraction, with the refractive index determined by the ratio of the speed of light in a vacuum to the speed in the medium.
• 😀 Total internal reflection occurs when the angle of incidence exceeds the critical angle, which is specific to each medium and can be calculated using Snell's law.
• 😀 Optical fibers rely on total internal reflection to transmit light, but modal dispersion can cause pulse broadening, which can be mitigated with thinner fibers or repeaters.
• 😀 Lenses use refraction to converge or diverge light rays, with convex lenses producing real or virtual images depending on the object’s distance, and the power of the lens being the reciprocal of its focal length.

Q & A

What is the main difference between longitudinal and transverse waves?

Longitudinal waves have oscillations that are parallel to the direction of energy transfer, with compressions and rarefactions. In contrast, transverse waves have oscillations that are perpendicular to the direction of energy transfer.

How do we calculate the frequency of a wave from a waveform?

To calculate the frequency, measure the time period (the time it takes for one complete wave to pass). Then, use the formula frequency (f) = 1 / time period (T).

What does the wave equation (V = f * λ) represent?

The wave equation represents the relationship between wave speed (V), frequency (f), and wavelength (λ). It shows how the speed of a wave depends on both its frequency and wavelength.

What is Snell's Law, and what does it describe?

Snell's Law is a formula that describes how light refracts when it passes from one medium to another. It is expressed as N1 * sin(θ1) = N2 * sin(θ2), where N is the refractive index, and θ1 and θ2 are the angles of incidence and refraction, respectively.

What is the critical angle, and how is it calculated?

The critical angle is the angle of incidence at which the angle of refraction is 90 degrees, meaning the light stays along the boundary. It can be calculated using the formula sin(θc) = N2 / N1, where θc is the critical angle, and N1 and N2 are the refractive indices of the two mediums.

How do optical fibers rely on total internal reflection?

Optical fibers use total internal reflection to keep light within the core of the fiber, allowing it to travel long distances. The core has a higher refractive index than the surrounding cladding, ensuring light is reflected back into the core rather than passing through the cladding.

What causes modal dispersion in optical fibers, and how can it be minimized?

Modal dispersion occurs when light rays take different paths through the fiber, leading to pulses spreading out over time. It can be minimized by making the fiber thinner or by using repeaters to reboost the signal periodically.

What is the difference between a convex and concave lens in terms of light behavior?

A convex lens converges light rays to a point called the principal focus, and can create real or virtual images depending on the object's distance. A concave lens diverges light rays, always producing a virtual image.

How do polarizing filters work with light waves?

Polarizing filters allow only light waves oscillating in a specific direction to pass through. When two polarizing filters are placed at right angles, no light passes through as all the light is absorbed by the second filter.

What is the principle behind Thomas Young’s double-slit experiment?

Thomas Young’s double-slit experiment demonstrated wave interference, where light passing through two slits forms a pattern of bright and dark fringes on a screen. This pattern occurs because of constructive and destructive interference between the light waves from the slits.