watch from 5.30 – 7.02
The cards the guy has used have many tiny lines. The lines on the card are on different angle. At a certain angle lights are able to pass through the card. When light are able to pass the card whatever is behind the card will appear normal but , when the card is turned a different way light will refract differently because the lines on the card; whatever behind the card appears banish . When the light hit the card light cannot pass-through, so light reflect by the lines on the card. When light cannot pass through also means what is a behind the card cannot see. This trick is similar with how polarization work too.
Constructive Interference is the interference of two or more waves of equal frequency and phase, resulting in their mutual reinforcement and producing a single amplitude equal to the sum of the amplitudes of the individual waves.
Destructive Interference is when the two amplitudes have opposite signs, they will subtract to form a combined wave with a lower amplitude.
a. Pulse Wave is a kind of non-sinusoidal waveform that is similar to a square wave, but does not have the symmetrical shape associated with a perfect square wave.
b. Periodic wave is a periodic function of one-dimensional space that moves with constant speed.
c. Transverse wave is a moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer.
d. Longitudinal waves are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of propagation of the wave.