# What was his argument about the absence of back wave?

## What was his argument about the absence of back wave?

It says ” Huygens argued that the amplitude of the secondary wavelets is maximum in forward direction and zero in the backward direction; by making this adhoc assumption, Huygens could explain the absence of backwave.

Is Huygens principle wrong?

“Actually Huygens’ principle is not correct in optics. It is replaced by Kirchoff’s (sic) modification which requires that both the amplitude and its derivative must be known on the adjacent surface. This is a consequence of the fact that the wave equation in optics is second order in the time.

What happens to wavelets Travelling in backward direction?

Students are always asking why the wavelets do not go out in the reverse direction as well as the forward direction when the medium is disturbed. Answer: If each wavelet radiates uni- formly in all directions, in addition to generating an ongoing wave there would also appear a back-wave traveling toward the source.

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### Why is the contribution of wavelets lying on the back of wave front 0?

The contribution of the wavelets lying on the back of the wave front is zero because of something known as the Obliquity Factor. It is assumed that the amplitude of the secondary wavelets is not independent of the direction of propagation.

Do the backward moving wavefront exist in Huygens wave model for light?

It adjusts the strength of the Huygen’s wavelets as a function of the direction of propagation of each segment of the wavelet so that there is no backward wave.

What is meant by backward wave?

THE term backward wave is applied to a wave in which the directions of the phase. velocity and the group velocity are opposite.

#### Why secondary wavelets are so important?

Due to the superposition of secondary wavelets, their major portions cancel Each Other effect by interference. Hence only the effective portions cancel Each Other effect by interference. Therefore, the only effective portions left are those where these secondary wavelets do not superpose each other.

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What is secondary wavefront?

The direction of propagation of light ray of light is. perpendicular to Wf. Every point on the given wave front acts as a source of new disturbance called secondary wavelengths which travel in all direction with the velocity of light in the medium. This is called secondary wavefront.

Which of the following produces a plane wavefront?

Plane Wavefront: When the small part of the spherical or cylindrical wavefront originates from a distant source, like infinity, then the wavefront which is obtained is known as a plane wavefront. For example: Rays coming from infinity, like Sun. Plane wavefront is generated from a very distant source.

## Why is it called backward wave?

Content: Backward Wave Oscillator It uses the principle of velocity modulation in order to build oscillations inside the vacuum tube. Basically in this tube, the wave travels in the opposite direction to the direction of movement of the electron beam. Thus it is known as backward wave oscillator or tube.

Does a backward wavefront exist in resonance?

A backward wavefront does exist in resonance. Think of a Helmholtz resonator. Sound hits a wall in a closed volume and then bounces back into itself. The wave fronts are simultaneously moving forward and backward. Nodes of amplitude form when the peaks of the forward wave coincide with the peaks of the backward wave.

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Why can’t a plane wave travel backwards?

I think the easiest explanation is that the backward-propagating portions are destructively interfered with by the wavelets from all of the other wave fronts. Imagine sending a plane wave through a hole. It diffracts outward, beyond the hole, in all directions.

### What happens when a sound wave hits a wall?

Sound hits a wall in a closed volume and then bounces back into itself. The wave fronts are simultaneously moving forward and backward. Nodes of amplitude form when the peaks of the forward wave coincide with the peaks of the backward wave. Wave equations are time-symmetrical, with inherently time-symmetrical fundamental solutions.

Do light waves travel backwards in the universe?

Therefore, we can say that with time passes light waves disperses at most that can be possible and forever. If they are retreating backward then arrow time will be backward then should not be going in disorderity but in ordered state or universe should be contracting all light waves and start moving towards singularity.