What is waves?
Wave is a transfer of energy from one point to another due to oscillation without physical transfer of matter
What is the difference between mechanical and EM waves?
- mechanical waves require medium while electromagnetic waves do not require medium
- mechanical waves propagate due to compression and rarefaction of molecules while EM waves consist of mutually perpendicular time-varying electric and magnetic fields
- mechanical waves’ speed depends on medium while EM waves travel at speed of light in vacuum
What are some examples of mechanical waves?
Sound, waves on string, water waves
What are some examples of EM waves?
Microwaves, visible light, gamma ray, X ray
What are transverse waves?
Waves where the plane of oscillations are perpendicular to the direction of energy propogation
What are longitudinal waves?
Waves where the plane of oscillations of the particles are parallel to the direction of energy propagation
What is the difference between transverse and longitudinal waves besides the direction of oscillations of the particles?
Transverse waves can be polarised while longitudinal waves cannot be polarised
What is a progressive transverse mechanical wave?
Energy and wave profile are propagated from one point to another due to vibrations. For transverse mechanical waves, there is no net transfer of matter
What is displacement?
Distance of a particle in a given direction from its equilibrium position
What is amplitude?
Maximum distance of a particle from equilibrium point
What is a wavelength?
- shortest distance between two particles that are in phase
- shortest distance between two crests
What is a period?
- time for a particle in the wave to complete one complete oscillation
- time taken for the wave to travel one wavelength
What is frequency?
The number of oscillations per unit time
What is speed of wave?
Distance travelled by the wave profile per unit time
What is a wavefront?
An imaginary line that joins all the points of the wave that are in phase
What is phase angle?
An angle in degrees or radians which measures fraction of a cycle that has been completed by an oscillating particle
What is phase difference?
Phase difference is the difference in oscillation stages as a fraction of a cycle between two points and two waves at a specific time, expressed in radians or degrees
What is polarisation?
Polarisation is where oscillations are restricted to one plane only, perpendicular to the direction of wave propagation
What is Malus law?
intensity of a light passing through an analyser and polariser is proportional to cos²θ, where θ is the angle through which the analyser has been rotated with respect to the polariser
How does a polarised transverse wave differ from an unpolarised transverse wave?
- For a polarised transverse wave, the oscillations are in a single plane, normal to the direction of energy transfer
- For an unpolarised transverse wave, the oscillations are in multiple planes and directions
Why can’t longitudinal waves be polarised?
In a longitudinal wave, the direction of vibration of particles is the same is the direction of wave propagation, hence there is no plane to restrict the movement of the vibrating particles
Why only transverse waves can be polarised by the polariser?
- For transverse mechanical wave, the vibration of the particles is perpendicular to the direction of wave motion
- Hence, the movement of the particles will be restricted in one plane if the plane of polarisation is parallel to the direction of wave motion
- For electromagnetic waves, the electric field component parallel to the axis of polarisation will be allowed to pass through, while its perpendicular component will be absorbed by the polariser
What is the principle behind the usage of Polaroid glasses used in 3D movies?
- The polarisation axis of the polaroid filters are set at right angles to each other - one horizontal and one vertical
- Each eye sees a separately polarised picture and the brain then interprets the two pictures as a single picture with depth, hence 3D effect is achieved
How does a polaroid polarise light?
- Electrons absorbed the energy of electric field components in the plane of the direction of travel of wave propagation
- Only vibrations of electric field components in the perpendicular plane can pass through
