Properties of Travelling Waves (reflection, refraction, diffraction, interference)

What are travelling waves?

• Aka continuing waves

• A wave that moves through a medium or space, transporting energy from one location to another

What is are the laws of reflection?

The laws of reflection state:

• The angle of incidence equals the angle reflection

• The incident ray, reflected ray, and the normal lie in the same plane

What is fixed end reflection?

The wave is inverted

Note: a thick string attached to a thin string acts as a fixed end

What is free end reflection

The wave is the same.

Note: a thin string attached to a thick string acts as a free end

What is refraction?

Refraction occurs when a ray bends when it passes from one medium to another (similarly to reflection) resulting in changes in the speed of light.

What is the index of refraction?

n = c / v

*the index of refraction is unitless

where c is the speed of light in a vacuum (3×10⁸ ms^-1) and v is the speed of light in the medium.

When does light travel slow?

• Light slows down when passing into a more optically dense medium

• The angle of refraction bends toward the normal (smaller)

When does light travel fast?

• Light speeds up when going from a denser to a less dense medium

• The angle of refraction bends away from the normal (further, fatter)

What are wavefronts?

• Equally spaced lines that represent in phase points on a wave

• The wavefronts are always perpendicular to the ray

• The gap between wavefronts represent the wave length

• Come in different shapes depending on the movement of the wave

What is snell’s law?

n₁sinθ₁ = n₂sinθ₂

What is the critical angle?

• The critical angle is the angle of incidence which results in the refracted angle being on the boundary at exactly 90 degrees

• Occurs only when light travels from more optically dense medium to a less optically dense medium.

What is total internal reflection?

• When the angle of incidence exceeds the critical angle, resulting in an angle of reflection instead of an angle of refraction

• Occurs only when light travels from a more optically dense medium to a less optically dense medium.

What is diffraction?

Diffraction is the bending and spreading of waves as they encounter an obstacle or pass through an opening.

What is Huygens’ Principle?

States that every point on a wave front is a source for a new wavelet. The new wave front is the tangential surface to all the wavelets.

What is superposition? (3)

Superposition is when waves are in the same physical location in the medium they move through.

• Amplitudes add together

• Once the waves move through each other, they continue to move in the direction they were travelling in originally

What is constructive interference?

When two amplitudes in the same direction add to produce a larger amplitude.

What is destructive interference?

When two amplitudes in the opposite direction cancel each other out to produce a smaller amplitude or no amplitude.