Railway Science (Physics-Light and Optics) (Part-II)

Pencil appears bent. Refraction is the bending of a wave when it enters a medium where its speed is different.The optical density of water is higher than that of the air. The light from the part of the pencil which is immersed in water, travels from water to air i.e, denser medium to rarer medium. Therefore, the light bends away from the normal and the pencil appears to be bent or broken.

Twice the distance between pole and F. Spherical mirror is formed by cutting out a piece of a sphere and silvering either the inside or outside surface. Two types: Concave Mirror and Convex Mirror. For spherical mirrors of small apertures, the radius of curvature is found to be twice the focal length.

Is negative (for real images). The height of the image of an object above the principal axis of a spherical mirror is positive (virtual images). Spherical mirror: The shape of a piece cut out of a spherical surface and silvering either the inside or outside surface. Two types: Concave Mirror (Converging mirror): Reflects light inwards to one focal point. Uses: Satellite Dishes, Headlights in a car, Shaving mirror, Dentist’s mirror. Convex Mirror (Diverging mirror): Reflects light outwards. Uses: Rearview mirror in vehicles, Security mirrors in ATMs.

Angle of deviation is the angle between the incident ray and the emergent ray of light after it passes through the prism. When white light is passed through a prism, it undergoes dispersion and splits into its constituent colors called spectrum. The angle of deviation is inversely proportional to the wavelength of light. Light with longer wavelength i.e. red deviates less and light with shorter wavelength i.e. violet deviates more.

Is parallel to the principal axis. Concave mirror (converging mirrors) is a spherical mirror whose reflecting surface is on the inner curved surface of the sphere. An incident ray starting or passing through the focus of a concave mirror travels parallel to its principal axis after reflection. Uses - Shaving mirrors, Headlights, Astronomical telescopes, Solar furnaces, Projectors, Makeup mirrors.

When parallel beam of light rays are incident on a convex mirror, the reflected rays appear to diverge from a point behind the mirror known as the virtual focus or focal point. In the case of a convex mirror, the virtual focus is located behind the mirror surface. The distance between the mirror surface and the virtual focus is equal to the focal length of the mirror, which in this case is 1 m. Hence, the reflected rays appear to diverge from a point at a distance of 1 m behind the mirror.

Orange. The refractive index of a particular colour is the reciprocal of its wavelength. The refractive index will be Red < Orange < Yellow < Green < Blue < Indigo < Violet . Wavelengths - Red > Orange > Yellow > Green > Blue > Indigo > Violet .

More in light of 4500 Å. The angle between the direction of incident ray and the emergent ray, is called the angle of deviation. Factors on which angle of deviation depends: angle of incidence, The wavelength of light used, the material of the prism, the angle of prism. Wavelength is the distance between identical points in the adjacent cycles of a waveform signal propagated in space or along a wire. SI unit is meter. Angle of deviation increases with decreases in wavelength. So, the angle of deviation is more in light of 4500 Å.

Image Formation by Concave Mirror- Object placed at- Infinity- Image is real and inverted and formed at the focus, Beyond the centre of curvaturereal image is formed between the centre of curvature and focus, At the centre of curvature- real image is formed at the centre of curvature, Between the centre of curvature and principal focus- real image is formed behind the centre of curvature, At the principal focus- real image is formed at infinity, between focus and pole- virtual and erect and image is formed behind the mirror.

Refractive index(n) is the measure of the bending of a light ray when passing from one medium to another.
Formula:- n=c/v.
c = speed of light in vacuum ,
v = phase velocity of light.
Refractive index of a medium depends upon- the wavelength of light, Density of the medium and Temperature.