Waves & Optics- Waves

Question 1

Waves

Answer 1

• A wave is just the propagation or storage of energy through a medium or the vacuum, without any transfer of the medium itself.
• Travelling waves transfer energy from one point to another through a vacuum or a medium.
• Standing waves do not transfer energy, but instead, store energy in the medium or vacuum.
• A wave can reflect, refract, diffract, exhibit interference, and in the case of transverse waves, can be polarised.
• There are many ways to categorise waves; electromagnetic waves, mechanical waves, progressive waves, standing waves, transverse, longitudinal, polarised, unpolarized, etc.
• The equation for the speed of the wave is v = λf, where v is the speed of the wave, f is the frequency of the wave and λ is the wavelength of the wave.

Question 2

Concepts

Answer 2

• Waves are defined by their wavelength and frequency
• Wavelength (λ) is the distance over which the shape of the wave repeats at a given time.
• Frequency (f) is the number of times the wave shape repeats the unit time at a given point. the inverse of frequency is the period (T), where T = 1/f
• Period (T) is the time it takes for the wave to repeat itself at a given point
• Wave speed (v) is the speed at which the wave propagates.
• Amplitude (A), the maximum displacement of the wave from its undisturbed position.
• Intensity of a wave is the average energy transferred through a unit area in unit time.

Question 3

Types of Waves

Answer 3

• Waves can be categorised as either longitudinal or transverse. These depend on the direction of the oscillation and the direction of propagation of the wave
• In transverse waves, the direction of oscillation is perpendicular to the direction of propagation.
• In longitudinal waves the oscillation is parallel to the direction of propagation.
• Examples of transverse waves can be water waves, seismic S waves and electromagnetic waves
• Examples of Longitudinal waves are sound waves, ultrasonic waves and seismic P waves.

Question 4

Phase and Phasors

Answer 4

• The phase of a point on a wave to the origin can be defined as the fraction of the wave cycle that has elapsed since the origin
• The phase difference can be represented as an angle or as pi radians.
• If you are superimposing two waves you just add the two phasors end to tip, with the resultant being the final displacement from the starting tail to the final tip.
• When superimposing two waves, there are three possible results, Constructive, which increases the strength of the wave, Destructive, which cancels out the energy of the wave and partial constructive which can slightly increase the power of the wave.

Question 5

De Broglie Wavelength

Answer 5

• matter and particles can exhibit wavelength properties, for example, electrons can diffract in the same way as light in the double-slit experiment.
• The de Broglie wavelength, λ, is the wavelength associated with a massive particle
• The equation for the de Broglie Wavelength is λ = h/p, where h is Planck’s constant and p is the momentum of the particle.