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What is Ray of Light?

Light is a form of electromagnetic radiation of any wavelength whether it is visible or not. Light is made up of small packets of energy called photons, consisting of waves of electromagnetic radiations. Photons do not possess any charge or resting mass and travel at the speed of light. In physics and optics, an idealized model of light drawn as a straight line is called a light ray. A light ray is always drawn with an arrow that implies the direction of the energy flow. Light rays are nothing but a model explaining the movements of light from one point to another. A group of light rays or a light beam, coming out from a source of light is known as a point source. 


Different Types of Beams of Light

Beams of light can be of 3 types. They are parallel, convergent and divergent.

Parallel: When rays from a distant point source travel parallel to each other in a particular direction, it forms a parallel light beam. The sunray is an example of a parallel beam of light.

Convergent: In a convergent beam, the light rays from a source of light, eventually meet or converge to a point.

Divergent: In a divergent beam, the light rays disperse away from a source of light.


Reflection of Light

Light rays change their direction while moving from one medium or when they are reflected off a surface. The law of reflection states that a light ray reflecting off an even surface has an equal angle of incidence and angle of reflection.


Refraction of Light

When a light ray travels from one transparent medium to another transparent medium, a portion of the light is reflected and another portion of the light is transmitted into the second transparent medium, changing the direction of the light. This phenomenon is defined as the refraction of light. 

The law of refraction or Snell's law states that the ratio of the sine of angles of incidence and refraction is equal to the ratio of the refractive index of the first and the second media respectively.


Mathematical Form

ratio of sin θ1 and sin θ2 (sin θ1 / sin θ2 ) = ratio of refractive index (n1 / n2)

or, 

n1 sin θ1 = n2 sin θ2

where,

θ1 = angle of incidence

θ2 = angle of refraction

The index of refraction of medium 1 and 2 are n1 and n2, respectively

A light ray from a lighter medium when entered into a denser medium bends towards the normal of the surface. On the other hand, a ray emerging from a denser medium entering into a lighter medium bends away from the normal. When the incident ray is equal to the normal of the surface, the direction of the light stays unaltered as it enters into the second medium.


Index of Refraction

The ratio of the speed of light in a vacuum to its speed in that particular medium is known as the refractive index or index of refraction. For example, the refractive index for a vacuum is always 1. The refractive index of air (standard conditions) is 1.0003, water is 1.3, and that of glass is 1.5.

By the law of reflection and the law of refraction, you can understand how a light ray travels. The law of reflection can be used to understand the images produced by different types of mirrors like a plane mirror, concave and convex mirrors. Whereas, Snell’s law can be used in lenses. For example, a human eye.



Solved Examples

1. A Ray of Light is Traveling Through the Air at an Angle of 30° to the Vertical. it Passes Into the Water Medium and the Angle Becomes Half the Vertical. What is the Index of Refraction of Water? θair=1.00

Ans: using Snell's law,

n1sin(θ1)=n2sin(θ2)

or, n2=n1sin(θ1)sin(θ2)

θ21/2=15o (as per question)

Solving by Snell's Law,

n2=(1.0)sin(30o) / sin(15o) = 1.93


2. What is a Refractive Index?

Ans. The ratio of the speed of light in a vacuum to its speed in that particular medium is known as the refractive index or index of refraction. For example, the refractive index for a vacuum is always 1. The refractive index of air (standard conditions) is 1.0003, water is 1.3, and that of glass is 1.5.


Conclusion

Here, we have covered the concept of light, a ray of light definition, different types of beams of light, the law of reflection, and the law of refraction. With the help of mathematical forms of the laws, you can solve various numerical problems related to ray and beam of light.

FAQs (Frequently Asked Questions)

1. State the Law of Refraction.

Ans. The law of refraction is employed by Snell. This law of refraction is also known as Snell's law. The law of refraction states that the ratio of the sine of angles of incidence and refraction is equal to the ratio of the refractive index of the first and the second media respectively. Now, we are going to discuss the mathematical formula of the law of refraction. 

The mathematical form of the law is- 

sin θ1 / sin θ2 = a1 / a2

or, a1 sin θ1 = a2 sin θ2

where,

θ1 = angle of incidence

θ2 = angle of refraction

Here, the index of refraction of medium 1 and 2 are a1 and a2, respectively. 

2. What are the Different Types of Light Beams?

Ans. Beams of light can be of 3 types. They are parallel, convergent and divergent. Here, we have mentioned the definition of these three types of light beams below. 


Parallel: When rays from a distant point source travel parallel to each other in a particular direction, it forms a parallel light beam. The ray from the sun is an example of a parallel beam of light.


Convergent: In a convergent beam, the light rays from a source of light, eventually meet or converge to a point.


Divergent: In a divergent beam, the light rays disperse away from a source of light.

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