Nature has bestowed us with vision to see the beautiful world. Human eye can detect electromagnetic waves within a small range of the electromagnetic spectrum. Electromagnetic radiation belonging to this region is called light. We are able to see and analyse things around us due to light and a sense of vision. The light travels very fast in seconds. It can travel from one point to another along a straight line. This path is called a ray of light. This is a very important chapter in physics for 12th standard students of CBSE Board. Solutions to all the questions in this chapter can be easily found in any good solution key that provides NCERT Solutions for Class 12 Physics. Reflection and refraction are true for all surfaces. The detail information is mentioned below:
Reflection
The laws of reflection states that the angle of reflection is equal to the angle of incidence. The incident ray, reflected ray and normal to the reflecting surface at the point of incidence lie in the same plane. The geometric center of the spherical mirror is called its pole while spherical lens is called its optical center. The line joining the pole and center of the spherical mirror is known as principal axis.
Refraction
The direction of incident ray of light that enters the other medium changes at the interface of two media. This phenomena is called the refraction of light.
- The incident ray, refracted ray and normal to the interface at the point of incidence all lie in the same plane.
- The ratio of angle of incidence to the angle of refraction is constant.
Demonstration of total internal reflection
All optical phenomena can be demonstrated at home with a simple technique by using laser torch Take a glass beaker with clear water. Stir the water with a piece of soap a few times, so that it turns a little turbid. Take a laser torch and shine its beam through the turbid water. You can observe that the path of the beam inside the water shines brightly. Also shine the beam below the beaker so that it strikes at the upper surface. Here you can see a partial refraction and reflection.
Natural phenomena due to sunlight
The colour that we see around is possible only because of sunlight. For example, blue sky, green landscape, rainbow etc. Let's discuss this with an example, a rainbow is formed due to dispersion of sunlight by the water drops in the atmosphere. This happens due to the combined effect of dispersion, refraction and reflection of sunlight. This is usually observed during the rainy day.
Scattering of light
When the sunlight travels through the earth's atmosphere. It is scattered by the atmospheric particles. The shorter wavelength of light is scattered more compared to longer wavelengths. For example, Sky. The sky is blue as it has shorter wavelength scattered more than the other colour red that has longer wavelength.
Optical Instruments
Eye
The most important optical device nature has bestowed is the eye.They are organs for the visual system. They provide vision to animals and humans. They detect light and convert to electrochemical impulses in neurons.They have rods and cons that have a sense of light and colour. The interior parts of the eye include cornea, iris and retina. Light enters through the cornea through curved surface then passes through the pupil, a center hole in the iris. The light is focused by retina. The retina contains rods and cones that can sense the light intensity and colour. And finally transmit electrical signals via optic nerve to the brain.
Microscope
It is a converging lens of small focal length. They are used to see micro objects such as cells, tissues of plants, animals and humans. In this the lens is placed near the object, and the eyepiece is positioned close to the lens on the other side. This gives a clear image of the object at a distance. There are two types of microscopes such as:
Simple microscopes: it consists of limited magnification
Compound microscope: it consists of two lenses objective and eyepiece for larger magnification.
Telescope
It is used to provide angular magnification of far away objects. This instrument consists of objective and eyepiece. The objective has a large focal length. The light from the distant object enters the objective where the real image is formed in the second focal point. The eyepiece magnifies the final image. Telescopes are generally used to see distant objects such as stars and the moon, specifically by researchers in the field of astronomy.
Solutions to all the questions in this chapter can be easily found in any good solution key that provides NCERT Solutions for Class 12 Chemistry .
The solid state should have properties like high temperature, magnetic materials, biodegradable polymers etc.
The general characteristics of solid state are as follows:Definite mass, shape and volumeShort intermolecular distancesStrong intermolecular forceConstituent particles have fixed position and can oscillate about their mean positionsRigidIncompressible Solids can be classified as amorphous and crystalline solids.Crystalline solids: The solids have more number of small crystals each having a definite geometric shape.
For example, NaCl, MgOMetallic solids: metals are the particles of metallic solids.
They are positive ions surrounded by free electrons.
For example, Fe, CuCovalent or network solids: covalent bonds are present in the solids that are strong and directional in nature.
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