# Forward and backward waves

• abaset
In summary, it is necessary to consider both forward and backward waves in the analysis of light off a dielectric slab or Fabry-Perot resonator, and this is especially important for oblique incidence.
abaset
Hi all;
In a reflection and transmission problem of light off a dielectric slab or Fabry-Perot resonator, is it necessary to describe the wave in the slab as a sum of forward and backward wave or just a forward wave propagate in the relevant direction is enough. ?
knowing that in the above medium, the wave in the medium of incidence is Ei +Er with Er = rEi and the field medium of transmittance is Et = tEi

In this case, is there any difference between oblique and normal incidence.

any insight is very much appreciated

Last edited:
.Yes, it is necessary to describe the wave in the slab as a sum of forward and backward waves. This is because, for oblique incidence, the forward and backward waves may have different amplitudes and phase shifts which must be taken into account for accurate analysis. For normal incidence, the forward and backward waves have the same amplitude and phase shift, so a single forward wave description is sufficient.

.

Hello,

In the study of light propagation in a dielectric medium, it is important to consider both forward and backward waves. This is because when light interacts with a dielectric slab or Fabry-Perot resonator, it can undergo both reflection and transmission. The reflected wave (Er) and transmitted wave (Et) are both components of the total incident wave (Ei). Therefore, it is necessary to describe the wave in the slab as a sum of both forward and backward waves.

In terms of normal and oblique incidence, there may be some differences in the way the waves propagate and interact with the medium. For example, at normal incidence, the reflected and transmitted waves will have the same polarization state as the incident wave. However, at oblique incidence, the polarization state may change due to the different refractive indices of the medium. Additionally, the amplitude and phase of the reflected and transmitted waves may also vary with angle of incidence.

I hope this helps to clarify the importance of considering both forward and backward waves in the study of light propagation in dielectric media. Thank you for your question.

## 1. What are forward and backward waves?

Forward and backward waves are types of waves that describe the direction in which energy or information is being transferred. In forward waves, the direction of energy transfer is in the same direction as the wave's propagation, while in backward waves, the direction of energy transfer is opposite to the wave's propagation.

## 2. What is the difference between forward and backward waves?

The main difference between forward and backward waves is the direction of energy transfer. In forward waves, energy is transferred in the same direction as the wave's propagation, while in backward waves, energy is transferred in the opposite direction.

## 3. How are forward and backward waves used in science?

Forward and backward waves are used in a variety of scientific fields, such as acoustics, optics, and electromagnetics. They are used to describe the behavior of different types of waves and to understand how energy and information are transferred.

## 4. Can forward and backward waves exist at the same time?

Yes, in some cases, forward and backward waves can exist simultaneously. This phenomenon is known as standing waves, where the forward and backward waves are equal in magnitude and cancel each other out, resulting in a stationary pattern.

## 5. What are some real-world examples of forward and backward waves?

Some common examples of forward and backward waves include sound waves, where the forward wave is the sound traveling towards the listener, and the backward wave is the sound reflecting off surfaces. In electromagnetic waves, the forward wave is the energy traveling through space, while the backward wave can be seen in the reflection or refraction of the wave. Additionally, water waves and seismic waves also exhibit both forward and backward components.

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