Light - Reflection and refraction

• Reflection of light is the phenomenon of bouncing back off the light rays in the same medium.
• Laws of Reflection: The incident ray, the reflected ray and the normal, all lie on the same plane at the point of incidence and the angle of incidence is equal to the angle of reflection.
• A real image is obtained when the rays of light after reflection or refraction actually meet at some point and can be obtained on the screen.
• A virtual image forms when rays of light do not actually meet, but appear to meet when produced backwards and cannot be obtained on the screen.
• The characteristics of the image formed by a plane mirror are virtual and erect, the size of the image is equal to the size of the object, the image is formed as far as behind the mirror as the object is in front of it, and it is laterally inverted.
• A spherical mirror whose reflecting surface is curved inwards is called a concave mirror.
• A spherical mirror, whose reflecting surface is curved outwards, is called a convex mirror.
• If the formed image is erect, of same size and equidistant as of object, then it is a plane mirror.
• If the image is erect, virtual but smaller in size, then it is a convex mirror.
• If the formed image is erect, virtual and magnified when the mirror is close to the object, then it is a concave mirror.
• The centre of the reflecting surface of a spherical mirror is called the pole of the mirror and it is usually represented by P.
• The horizontal line passing through the centre of curvature and pole of the spherical mirror is known as principal axis.
• The centre of curvature of a spherical mirror is the centre of the hollow sphere of glass, of which the spherical mirror is a part and is usually represented by C.
• The radius of curvature of a spherical mirror is the radius of the hollow sphere of glass, of which the spherical mirror is a part and is usually represented by R.
• The diameter of the reflecting surface, i.e., twice the radius is called its aperture.
• The principal focus is the point on principal axis through which the rays of light which are parallel to it pass after reflection or they appear to be arising from this point.
• A ray parallel to the principal axis will pass through the principal focus, after reflection.
• A ray passing through the principal focus of concave mirror will be parallel to principal axis after reflection.
• A ray of light passing through the centre of curvature of a concave mirror is reflected back along the same path as it is a normally incident ray at the mirror surface.
• A ray incident obliquely to the principal axis of a concave mirror is reflected obliquely making equal angle with the principal axis.
• Image formation by a concave mirror for different positions of the object: Position of Object Position of Image Size of Image Nature of Image At infinity At the focus F Highly diminished/ point-sized Real and inverted Beyond C Between F and C Smaller in size Real and inverted At C At C Same size Real and inverted Between C and F Beyond C Enlarged Real and inverted At F At infinity Highly enlarged Real and inverted Between P and F Behind the mirror Enlarged Virtual and erectImage formation by a convex mirror for different positions of the object: Position of Object Position of Image Size of Im
• The phenomenon of change in the path of light from one medium to another is called refraction of light.
• The angle formed between the incident ray and the normal is called angle of incidence and the angle formed between the refracted ray and the normal is called angle of refraction.
• The cause of refraction is the change in the speed of light as it goes from one medium to another medium.