- Books Name
- CBSE Class 7 Science Book
- Param Publication
- CBSE Class 7
Reflection of light :
When a ray of light falls upon a smooth surface like a mirror, the ray of light is reflected in another direction in the same medium. This phenomenon is called reflection of light.
(a) General definitions about reflection :
(i) Mirror :
A smooth polished surface from which regular reflection can take place is called mirror. MM’ is the mirror as shown in figure.
(ii) Incident ray :
A ray of light which travels towards the mirror is called incident ray. Ray AB is incident ray in figure.
(iii) Point of incidence :
The point on the mirror, where an incident ray strikes is called point of incidence. ‘B’ is the point of incidence in figure.
(iv) Reflected ray :
A ray of light which bounces off the surface of a mirror, is called reflected ray. BC is reflected ray in figure.
(v) Normal :
The perpendicular drawn at the point of incidence, to the surface of mirror is called normal. BN is the normal in figure.
(vi) Angle of incidence :
The angle made by the incident ray with the normal is called angle of incidence. ∠ABN is the angle of incidence in figure. It is denoted by ∠i.
(vii) Angle of reflection
The angle made by the reflected ray with the normal is called angle of reflection. ∠CBN is the angle of reflection in figure. It is denoted by ∠r.
(viii) Glance angle of incidence
The angle which the incident ray makes with the mirror is called glance angle of incidence.
∠MBA is the glance angle of incidence in figure.
(ix) Glance angle of reflection
The angle which the reflected ray makes with the mirror is called glance angle of reflection. ∠M’BC is the glance angle of reflection in figure.
Regular and diffused reflection :
When a beam of light falls on a smooth, highly polished surface, almost entire light gets reflected in the same medium in a definite direction. This type of reflection is called regular reflection. We can see our image formed by a mirror due to the phenomenon of regular reflection.
When a beam of light falls on an opaque, rough and uneven surface, the light gets reflected in different directions. This type of reflection is called irregular or diffused reflection. We can read a book or a newspaper due to diffused reflection.
Laws of Reflection :
The reflection of light from a surface obeys certain laws called laws of reflection. They are :
(i) The angle of incidence is equal to the angle of reflection. i.e., ∠i = ∠r.
(ii) The incident ray, the reflected ray and the normal at the point of incident, all lie in the same plane.
The laws of reflection are applied for all type of reflections.
Ex.1 Calculate the angle of reflection.
Sol. According to the law of reflection, incident angle equal to reflected angle. So angle of reflection ∠r = 30°.