The refractive index for red light in glass is slightly different than for violet light. Violet light slows down even more than red light, so it is refracted at a slightly greater angle. The refractive index of red light in glass is 1. The refractive index of violet light is 1. This slight difference is enough for the shorter wavelengths of light to be refracted more.
A rainbow is caused because each colour refracts at slightly different angles as it enters, reflects off the inside and then leaves each tiny drop of rain. A rainbow is easy to create using a spray bottle and the sunshine. The centre of the circle of the rainbow will always be the shadow of your head on the ground.
The secondary rainbow that can sometimes be seen is caused by each ray of light reflecting twice on the inside of each droplet before it leaves. This second reflection causes the colours on the secondary rainbow to be reversed. Red is at the top for the primary rainbow, but in the secondary rainbow, red is at the bottom. Learn more about the many different kinds of rainbows and how they are formed from the Atoptics website — Rainbows reflect and Rainbow orders.
Learn more about human lenses, optics, photoreceptors and neural pathways that enable vision through this tutorial from Biology Online. Rule 1 : A ray of light parallel to the principal axis of the concave lens appears to be coming from focus after refraction through the lens. Rule 2: A ray of light passing through the optical centre of the concave lens goes straight after refraction through the lens. Rule 3 : A ray of light going towards the focus on another side of the concave lens becomes parallel to the principal axis after refraction through the lens.
Case 1: When an object is placed anywhere between optical centre and infinity, the image formed is between optical centre and focus. Case 2: When an object is placed at infinity, the image formed by concave lens will be at focus. A measure of the degree at which a lens can converge or diverge, light rays falling on it is called power of lens. A lens of short focal length has more power compared to a lens with long focal length.
The SI unit of the power of lens is dioptre. The combination of lenses is used in cameras, microscopes, telescopes etc.
Combination of lenses increases the sharpness of the image which is free from many defects. Are you worried or stressed? Click here for Expert Advice. Comment 0. Post Comment. Disclaimer: Comments will be moderated by Jagranjosh editorial team. Comments that are abusive, personal, incendiary or irrelevant will not be published. Please use a genuine email ID and provide your name, to avoid rejection.
Refraction of light by Spherical Lenses Refraction is the change in direction of light when it passes from one medium to another. Lens is a piece of transparent glass bound by two spherical surfaces and is used to magnify objects. If the refracted rays are extended backwards behind the lens, an important observation is made.
The extension of the refracted rays will intersect at a point. This point is known as the focal point. Notice that a diverging lens such as this double concave lens does not really focus the incident light rays that are parallel to the principal axis; rather, it diverges these light rays.
For this reason, a diverging lens is said to have a negative focal length. The first generalization can now be made for the refraction of light by a double concave lens:. Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point i. Now suppose that the rays of light are traveling towards the focal point on the way to the lens.
Because of the negative focal length for double concave lenses, the light rays will head towards the focal point on the opposite side of the lens. These rays will actually reach the lens before they reach the focal point. The above diagram shows the behavior of two incident rays traveling towards the focal point on the way to the lens. A second generalization for the refraction of light by a double concave lens can be added to the first generalization. The above discussion focuses on the manner in which converging and diverging lenses refract incident rays that are traveling parallel to the principal axis or are traveling through or towards the focal point.
But these are not the only two possible incident rays. There are a multitude of incident rays that strike the lens and refract in a variety of ways.
Yet, there are three specific rays that behave in a very predictable manner. The third ray that we will investigate is the ray that passes through the precise center of the lens - through the point where the principal axis and the vertical axis intersect. This ray will refract as it enters and refract as it exits the lens, but the net effect of this dual refraction is that the path of the light ray is not changed. For a thin lens , the refracted ray is traveling in the same direction as the incident ray and is approximately in line with it.
The behavior of this third incident ray is depicted in the diagram below. Now we have three incident rays whose refractive behavior is easily predicted. These three rays lead to our three rules of refraction for converging and diverging lenses.
These three rules are summarized below. They also apply to light passing through lenses. Refraction with lenses The bending of a ray of light also occurs when light passes into and out of a glass lens. However, because of the curved surfaces of the lens, the bending causes the light rays in a beam either to come together converge, picture on left-hand side or to spread out diverge, picture on right-hand side. Because a convex lens can cause rays of light to converge, it can produce an image on a screen.
This is called focusing an image onto a screen a real image. The concave lens spreads the light rays out and so it cannot focus an image onto a screen.
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