DP IB Physics: SL
C. Wave behavior
C.3 Wave phenomena
DP IB Physics: SLC. Wave behaviorC.3 Wave phenomena
Guiding questions: | |
|---|---|
| a) | How are observations of wave behaviours at a boundary between different media explained? |
| b) | How is the behaviour of waves passing through apertures represented? |
| c) | What happens when two waves meet at a point in space? |
a) How are observations of wave behaviours at a boundary between different media explained?
- Solution:
- A wave may behave in one of three ways when it comes into contact with a barrier between distinct media: transmission (moving through), refraction (bending), or reflection (bouncing back).
- The shift in the wave’s direction and speed as it moves into the new medium explains these behaviours. A change in wave speed may also result in a change in wavelength.
- Figure 1 Reflection and refraction of waves
- Reflection:
- Reflection is the process by which a wave strikes a boundary and returns to its original medium. The angle of incidence, or the angle at which the wave strikes the boundary, and the angle of reflection, or the angle at which it bounces off, are equal.
- Refraction:
- A wave may bend or change direction if it crosses the border into a different medium because of a change in speed. We refer to this bending as refraction. Light, for instance, bends when it moves from air to water.
- Transmission:
- A portion of the wave’s energy may enter the new medium through the barrier. Transmission is what this is.
- Absorption:
- The new medium may also absorb the wave’s energy, frequently in the form of heat.
b) How is the behaviour of waves passing through apertures represented?
- Solution:
- Waves spread out when they pass through an aperture, which is a tiny hole. The aperture’s size in relation to the wave’s wavelength determines how much of this spreading occurs.
- Spreading is negligible if the aperture is significantly greater than the wavelength. The spreading is more noticeable and the wave seems to bend around the opening’s borders if the aperture is equal to or less than the wavelength.
- Figure 2 The double-slit experiments
- Diffraction:
- The phenomenon known as diffraction occurs when waves bend around the edges of holes or obstructions.
- Aperture Size:
- Diffraction is greatly impacted by the aperture’s size. The wave will pass through with little bending if the aperture is significantly bigger than the wavelength.
- Wavelength and Aperture:
- A wave will spread out significantly after passing through an aperture if its wavelength is equal to or greater than its aperture size.
- Representation:
- The wavefronts of the wave after it has passed through the aperture are frequently used to illustrate diffraction. The curved wavefronts will show that the wave is expanding.
- Example:
- Sound waves moving through a doorway are a typical example. Since sound waves bounce off the door’s edges, you may hear sounds coming from various locations in the room if it’s open.
- Huygens’ Principle:
- Diffraction is explained by Huygens’ Proposition. Secondary spherical wavelets can be thought of as originating from any location on a wavefront. The new wavefront is formed by the envelope of these wavelets.
-
c) What happens when two waves meet at a point in space?
- Solution:
- When two waves collide at a place, their amplitudes combine to form either a destructive interference or a constructive interference, which is a bigger wave.
- The alignment of the waves’ crests and troughs determines whether the interference is constructive or destructive.
- Figure 3 Wave interference
- Principle of superposition:
- The principle of superposition states that the displacements (or amplitudes) of waves that overlap add up at every location in space.
- Figure 4 Superposition of waves
- Constructive Interference:
- Two waves will have a greater amplitude if their crests line up (and the same is true for their troughs). This is as a result of the constructive accumulation of displacements.
- Destructive Interference:
- The displacements will partially or totally cancel each other out if the peak of one wave coincides with the trough of another. The waves might totally cancel out, producing a wave with zero amplitude, if they are identical and exactly out of phase.
- Phase Difference:
- The waves’ phase difference dictates how the crests and troughs line up. Constructive interference happens when the phase difference is zero or an integer multiple of 2π. Destructive interference happens when the phase difference is π or an odd multiple of π.
- Figure 5 Phase difference