laws of reflection and refraction

Light

       “Light is electromagnetic radiation that can be detected by the human eyes. Light affects the retina of our eyes.”

     Light is a disturbance of electric and magnetic fields that travels in the form of a wave. Imagine throwing a pebble into a still pond and watching the circular ripples, each light wave has a series of high points known as crests, where the electric field is highest, and a series of low points known as troughs. The number of wave crests that pass through a given point in one second is called the frequency, measured in units of cycles per second called Hertz. The speed of a light wave equals the frequency times the wavelength.

What are the properties of light?

Important properties of light

( i )  Light is a form of energy.

( ii )  Light is a type of electromagnetic wave.

( iii )  Light travels in a straight line.

( iv )    The speed of light is maximum in a vacuum (about `c = 3 \times 10^8 m / s`).

( v )    The wavelength of light is from zero to infinity. (`\lamda = 0`  to `\infty`)

( vi )    Light consists of the ultraviolet region, the visible region, and the infrared region.

( vii )    The phenomenon of reflection, refraction, diffraction, polarization, interference, photoelectric effect, Raman effect, etc. is found in light.

( viii )    According to Newton, light is of particle nature, these particles are called light corpuscle, these light particles move at the speed of light in a vacuum, the size of  red particles are the largest.

( ix )    According to Hygiene, light is of wave nature, the wavelength of these waves is maximum for red color.

( x )    According to de Broglie, light is of dual nature.

( xi )    According to Einstein `E = mc^2`

( xii )   According to plank `E = h \nu`

( xiii )    The surface on which the light rays fall heats that surface.

( xiv )  Light rays exert pressure on the surface on which they fall.

What is Reflection of Light ?

Reflection of Light

Reflection of Light

  “When light rays strike a shiny surface, they return back to the same medium, this phenomenon of light is called reflection. The speed of light remains constant in the event of reflection.”

Reflection of Light

    When a ray of light approaches a smooth polished surface and the light ray bounces back, it is called the reflection of light. The incident light ray which lands upon the surface is said to be reflected ray. If a perpendicular were to be drawn on reflecting surface, it would be called the normal. 

Laws of Reflection

First Law of Reflection: The incident ray, normal, and the reflected ray all lie in the same plane.

Second Law of Reflection: The angles of incidence and reflection are equal.

 Angle of incidence = Angle of reflection

        `\angle i = \angle r`

Angle of incidence

    The angle between the incident ray and the normal is called the angle of incidence.

Angle of Reflection

    The angle formed between the reflected ray and the normal is called the angle of reflection.

Speed of light

    The speed of light is maximum in a vacuum (about `c = 3 \times 10^8 m / s`). The speed of light is 299792458 meters per second.

Formation of Image by the Plane Mirror

    The image formed by the plane mirror is always virtual and of the same size as that object.

Properties of the Image Formed by a Plane Mirror

    If the image is formed by the plane mirror then it has the following characteristics:-

( i ) The size of the image is equal to the size of the object.

( ii) The object distance = Image distance

(iii) The image is virtual and erect.

(iv) To get an image of the same size as that of object, the length of the mirror should be half of the length of the object.

( v) When a mirror is rotated through a certain angle, the reflected ray is rotated through twice this angle. ( For any incident ray if mirror is rotated by angle `\theta`, then the reflected ray rotates by angle 2`\theta`)

(vi) If the object is moving towards the plane mirror or away from the mirror with velocity `v`, the image will move towards the mirror or away from the mirror with velocity equal to `2v`

(vii) If the two plane mirrors are inclined at an angle `\theta`, then the number of images formed of an object placed between the mirrors will be

(a)   ` n = \frac{360^\circ}{\theta} - 1`   if  `\frac{360^\circ}{\theta}` is even integer.

(b)    ` n = \frac{360^\circ}{\theta}`   if  `\frac{360^\circ}{\theta}` is odd integer. 

(viii)    The image formed by a plane mirror: The left side of the object is seen on the right side in the image, and right side of the object appears to he on the left side in the image. This is known as lateral inversion.

What is the Refraction of light?

Refraction of light

Refraction of light

    Refraction is the phenomenon of bending of light, when light rays enter from one medium to another, then it bends from its original path, this phenomenon is called refraction. This is due to the change in the speed of light when it passes from one medium to another.

Causes of Refraction          

 

    A change of speed changes the Direction of light. The change in the speed of light results in a change in the direction of the light ray.

Laws of Refraction of Light

First Law of Refraction of Light:

The incident ray, the normal, and the refracted ray all lie in the same plane.

Second Law of Refraction of Light:

or Snell's Law -

    The ratio of sin of the angle of incidence and angle of refraction is constant for a particular medium.

`\mu = \frac{sin i}{sin r}`

This constant is called the refractive Index.

    It is actually called the refractive index of the second medium with respect to the first medium.

Types of reflection

Reflection- Bouncing back of light after striking any surface is known as reflection. Reflection are of two types-

Regular Reflection-This happens when light strikes a smooth polished surface and angle of incidence is equal to angle of reflection. this happens in case of mirrors.

Regular Reflection

Irregular Reflection- This happens when light strikes a rough/irregular surface and angle of incidence is not equal to angle of reflection and light bounces off in random directions.

Some real-life Experience

(i)A coin placed in water appears slightly raised. Stars twinkle in the sky.

(ii)A pencil immersed in water appears to be bent.

(iii)The sun becomes visible 2 minutes before sunrise and up to two minutes after sunset, thus increasing the length of the day by 4 minutes.

Why does the speed of light change when it passes through a medium?

    The speed of light can vary between different mediums because light is an electromagnetic wave, and the speed at which it travels through a medium depends on the properties of that medium. The speed of light in a medium is related to the refractive index of that medium, which is a measure of how much the medium can bend light. The refractive index of a medium is determined by the density of the medium and the electromagnetic properties of its molecules. In general, the higher the refractive index of a medium, the slower the speed of light.

    For example, light travels more slowly through water than it does through air because water has a higher refractive index than air.

What happen when light falls on a mirror?

    When light falls on a mirror, the direction of light changes. This change in direction of light is called reflection. The angle of reflection depends upon the angle of incidence of the light beam upon the surface of the mirror. The reflection also depends upon the type of the mirror (concave, convex or plane).

(or)

    When light falls on the mirror, the phenomenon of reflection takes place in the light. In the phenomenon of reflection, there is a change in the direction of light. In the phenomenon of reflection, the medium does not change and the angle of reflection and the angle of incidence are equal. The image also depends on the type of mirror (concave, convex or plane).