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

𝑅/2 = 𝑓.  A spherical mirror is
a mirror that has the shape of a piece cut out of a spherical surface.

θ = β. In an equilateral triangle the refracted ray inside the prism is parallel to the base. In an equilateral prism the angle made by the emergent ray with the normal at the surface is equal to the angle made by the ray with the normal at the refracting surface. This is because the prism is equilateral and therefore the ray will make the same angle with both the faces. θ = angle of incidence, β = angle of emergenc.

Short, distraction. Blue light has shorter waves, with wavelengths between about 450 and 495 nanometers. Red light has longer waves, with wavelengths around 620 to 750 nm. Scattering of light is the phenomenon that makes the path of light visible. When a beam of light strikes fine particles present in the atmosphere, scattering happens.

The laws of reflection of light are applicable to both plane and curved surfaces. For both, plane and curved surfaces, the incident ray, the reflected ray and the point of incidence, all lie on the same plane. So, statement A is incorrect. When a ray of light is incident obliquely towards the pole of a concave mirror or a convex mirror, it is reflected obliquely in such a way the incident and reflected rays make equal angles with the principal axis. So, statement B is incorrect. Hence, Both statements A and B are incorrect.

Infinity and convex mirror. Convex mirrors form virtual, diminished and erect images. Position of object - At infinity, Position of image - Highly diminished, point size image at the focus F, Behind the mirror. Position of object - Between infinity and pole, Position of image - Diminished image between pole and focus.

Refraction of light is the change in the direction of a light wave passing from one medium to another. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant.

Only (B) and (D). Concave Mirror: Curved inward and away from the light source, forms both real and virtual images. Convex Mirror: Diverging mirror, forms virtual and erect images. Ray diagram of the spherical mirror - When a ray strikes a spherical mirror obliquely at its pole, it is reflected obliquely making the same angle with the principal axis. When a ray, parallel to the principal axis strikes a spherical mirror, the reflected ray passes through the focus on the principal axis.

Its Speed. The speed of light decreases when it enters from a rarer medium to a denser medium and increases when it enters from a denser medium to a rarer medium. The speed of light increases when a light ray passes from water to air and the speed of light decreases when a light ray passes from water to glass. It is known as the phenomenon of refraction. The refractive index of water with respect to air is 1.33.

Atmospheric refraction of starlight. When the light coming from a star enters the earth's atmosphere, it undergoes refraction due to the varying optical densities of air at various altitudes. The atmosphere is continuously changing (because optical densities of air at different levels in the atmosphere keep on changing). The star-light reaching our eyes increases and decreases continuously due to atmospheric refraction and the star appears to twinkle at night.