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

Dispersion :- The splitting of light into its component colors. Example: Rainbow - Colors of rainbow (Red, orange, yellow, green, blue, indigo, violet).

Concave mirror. Other Uses Of Concave Mirror - Head mirrors, Ophthalmoscope, Headlights, Solar furnaces, Astronomical telescope.

Lens formula : 1/v - 1/u = 1/f
Other related Formulas: Radius of curvature = 2 × focal length, Snell's formula n = sin i / sin r (Where i is the angle of incidence and r is the angle of refraction),
Mirror Formula →  1/v + 1/u = 1/f
(Where f is the focal length, v is the image distance and u is the object distance), Power of a lens P = 1/focal length , Magnification (mirror) = height of image/ height of object.

Infrared. Infrared (IR) light is used by electrical heaters, cookers for cooking food, optical fibers, security systems and thermal imaging cameras which detect people in the dark. Ultraviolet radiation is widely used in industrial processes and in medical and dental practice. X- ray used to scan bone fractures.

Diminished. Concave lens: A lens that diverges the beam of light. The light from the source is refracted as a diminished, virtual or real, and vertically inward image. Examples: Binoculars, Telescope, Eyeglass, Flashlight, Spyholes indoors. Image Formation: Object at Infinity: A virtual, erect, highly diminished in size, and of point size. Object between Infinity and Optical Centre: A virtual, erect, and diminished-sized picture of the object is formed between the concave lens’s focus and optical center.

Between F₁ and 2F₁ . Convex lens: That converging rays of light that convey parallel to its principal axis (i.e. converges the incident rays towards the principal axis) which is relatively thick across the middle and thin at the lower and upper edges. The edges are curved outward rather than inward. Images formed are real and inverted when the position of the object is: At infinity {Image (Highly diminished) - At focus F₂}, At 2F₁ {Image (Same size) - At 2F₂}, Beyond 2F₁ {Image (diminished) - Between F₂ and 2F₂}, At focus F₁ {Image (highly enlarged) - At Infinity}.

Parallel to the principal axis. Refraction Through a Concave Lens: When an object is placed at infinity, a point-sized (highly diminished), virtual and erect image is formed at the focus. When an object is placed at a finite distance from the lens (or between infinity and optical centre O of the lens), a diminished, virtual and erect image is formed between the optical center and focus of the concave lens.

Towards the normal. Refraction is the bending of light as it passes from one transparent substance into another. In a rarer to a denser medium, the ray of light bends towards normal and in a denser to a rarer medium, the ray of light bends away from normal.

Concave mirror: A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of the sphere. It is commonly used in torches, search-lights and vehicle headlights to get powerful parallel beams of light. It is used as shaving mirrors to see a larger image of the face.

Principal focus. The Centre of curvature (C) is the center of a sphere of which a lens is formed. Focal length is the distance between the optical center and the principal focus of a lens. Optical center is the center point of a lens. A concave lens is a lens that diverges a straight light beam from the source to a diminished, upright, virtual image.