The spherical mirror used in a beauty parlour as make-up mirror is (convex mirror, concave mirror).
Important Points to Remember in Chapter 3 - Light from Tamil Nadu Board Standard Eight Science Solutions
1. Laws of Reflection:
(i) Light is an invisible energy which causes the sensation of vision.
(ii) Light energy always travels in straight lines.
(iii) Incident ray: A ray of light which travels towards a mirror or some other medium.
(iv) Angle of incidence: The angle which the incident ray makes with normal at the point of incidence.
(v) Angle of reflection: The angle which the reflected ray makes with normal at the point of incidence.
(vi) There are two laws of reflection:
(a) incident ray, reflected ray and the normal lie in the same plane at the point of incidence,
(b) angle of incidence is always equal to the angle of reflection.
2. Regular and Diffused Reflection:
(i) Regular reflection: The phenomenon due to which a parallel beam of light is reflected as a parallel beam in some other direction.
(ii) Diffused reflection: When a parallel beam of light on striking some rough surface gets reflected in different directions.
(iii) Mirror: A highly polished surface from which reflection takes place.
(iv) Real image: An inverted image which can be projected on the screen.
(v) Virtual image: An erect image which cannot be taken on the screen.
(vi) When the left side of the object appears as the right side of an image or vice versa, the image is said to be laterally inverted.
(vii) The image formed in a plane mirror is virtual, erect, laterally inverted and is formed as far behind as the object is in front of a plane mirror.
3. Multiple images:
Kaleidoscope: A toy made by joining three plane mirror strips at an angle of , such that coloured objects placed in it form beautiful hexagonal patterns.
4. White or Coloured:
(i) Dispersion: The phenomenon due to which white light splits into seven colours.
(ii) Spectrum: A band of seven colours formed on the screen, when white light splits into its constituent colours.
(iii) A prism breaks white light into seven colours to form spectrum, such that the red colour bends least, and the violet colour bends most.
5. Refraction:
(i) For given pair of medium, and given colour of light, the ratio between the sine of angle of incidence and sine of angle of refraction is constant and equal to relative refractive index of medium 2 with respect to medium 1.
(ii) Incident ray, refracted ray, normal drawn to the interface, at the point of incidence, lie in a same plane.
(iii) The rays of light while travelling from rarer to denser medium bend towards the normal drawn at the point of incidence. The rays travelling from a denser to a rarer medium, bend away from the normal.
(iv) Refractive index of a medium
(v) A prism breaks white light into seven colours so as to form spectrum, such that the red colour bends least, and the violet colour bends most.
