## What is Reflection of Light?

When the light ray falling from the object on the surface bounces back are known as reflected rays and this phenomenon is known as a reflection of light.

## What are Laws of Reflection?

The laws of reflectionÂ are divided into two main points and they are:

- The angle of reflection of the reflected ray is equal to the angle of incidence at the point of reflection
- The incident ray, reflected ray, and the reflection point all lie on the same plane.

## Characteristics of Image formed by Plane Mirror

Following are the characteristics of image formed by plane mirror:

- The image obtained by the plane mirror is always erect and virtual.
- The image size and the size of the object, both are equal.
- The distance between the image obtained is as the distance at which the object is placed.
- Laterally inverted images are obtained.

### Image Formed by the Plane Mirror

Consider the light rays 1, 2 and 3 shown by solid lines. The wavefronts which are perpendicular to these light rays are shown by the thin lines. The secondary wavefronts generated are the circular fronts described.

At point a, a wavefront is generated due to the secondary source on ray 2. At the same time, other wavefronts are generated at points *c* and *b*. Since wavefronts at points,Â *a *and *b* are generated at the same time *ac*** = ***cb**.* Thus the triangle *a**cb* is isosceles and the angles *Î¸ _{1 }*

**=**

*Î¸*

_{2}.Note that *Î¸ _{1}* is the angle of incidence and

*Î¸*is the angle of reflection.

_{2}Thus,

**Angle of incidence = Angle of reflection**

*Below is theÂ image formed by the plane mirror*

### Huygens Principle and Law ofÂ Refraction

Consider the light rays 1, 2 and 3 shown by solid lines refracted to rays 1â€™, 2 and 3â€™ respectively. The wave fronts which are perpendicular to these light rays are shown by the thin lines. Consider the wave fronts to be one wavelength apart in their respective media where refractive indices n_{1 }< n_{2}.Â The incident angle is Î¸_{1 }and the refracted angle is Î¸_{2}.Â Consider the wave front at c, the front is bent in the new medium because the speed of light is slower. However, since the frequency of the waves are a constant, the wavelengths change across media to accommodate the change in speed.

i.e.,

\(Ï‘_1\) = \(Ï‘_2\)

\({v_1}{Î»_1}\) = \({v_2}{Î»_2}\)

Also from figure the side ac is common to the triangles *abc* and *adc,*

\(ac\) = \(ac\)

\(\frac{bc}{sinÎ¸_1}\) = \(\frac{ad}{sinÎ¸_2}\)

But the line segments *ac* and *ad* represent the wavelengths in their respective media,

\(\frac{Î»_1}{sinÎ¸_1}\) = \(\frac{Î»_2}{sinÎ¸_2}\)

\(\frac{v_1}{sinÎ¸_1}\) = \(\frac{v_2}{sinÎ¸_2}\)

\(\frac{sin~ Î¸_1}{sin~Î¸_2}\) = \(\frac{v_1}{v_2} \)

\(\frac{sin~Î¸_1}{sin~Î¸_2}\) = \(\frac{\frac{c}{v_2}}{\frac{c}{v_1}}\) = \({n_2}{n_1} \)

Where, c is the speed of light in vacuum.

Thus, the Huygens principle can be used to prove the law of refraction. A similar exercise can be conducted for n_{1 }> n_{2}.