SPHERICAL MIRRORS

What is a spherical mirror? Spherical mirrors are mirrors whose surfaces form a part of a hollow sphere, The spheres can be made of glass or any polished metal surfaces Types of spherical mirrors : 1. Convex Mirror 2. Concave Mirror

Convex mirror :. If the silver coating is in the inside of the spherical surface, then the mirror is called a convex mirror Concave mirror :If the siver coating is on the outside of the spherical surface, then the mirror is called a concave mirror.

Some definitions of convex and concave mirrors 1.Center of curvature : It is the center of the hollow sphere from which the mirror has been cut. It is represented by the letter C. Any line joining a point on the mirror to C, is normal at that point of the mirror.

Some definitions of convex and concave mirrors 2. Radius of curvature : Radius of curvature is the radius of the sphere from which the mirrors (either convex or concave) is made. It is represented by the letter R. In the figure, the distance CP is the radius of curvatures of the two mirrors.

Some definitions of convex and concave mirrors 3.Pole of the mirror : The central point on the surface of the mirror is called the pole of the mirror. It is represented by the letter P. It is the center of the aperture of the mirror

Some definitions of convex and concave mirrors 4.Principal axis of the mirror : A straight line that passes through the center of curvature C and the pole P of the mirror, is called the principal axis of the mirror. In the figure, line XY is the principal axis of the mirrors.. A ray of light passing along the principal axis will be reflected back along the same path.

Some definitions of convex and concave mirrors 5.Aperture of the mirror : The portion of the hollow spherical surface from which the mirror reflections take place is called the aperture of the mirror. In the figure 2, the distance MM’ is the aperture of the mirror.

Some definitions of convex and concave mirrors 6.Focal Length of a mirror : When parallel rays of light coming from an infinite distance, fall on either a concave or a convex mirror, they are reflected back to a point on the principal axis XY. The focus is where the image is formed of an object placed at a far distance.

Focal length of a concave mirror : In a concave mirror, the rays,after reflection actually converge at a point F. The distance PF is called the focal length and F is called the focal point. The focus is in front of the mirror.

Focal length of a convex mirror :- In convex mirrors, the parallel rays, on reflection, appear to diverge from a point F. This point is called the focal point of the convex mirrors and the distance PF is called the focal length. The focus, in this case is behind the mirror

Real and Virtual images 1. In a concave mirror, the focus is real. The object and the image lie on the same side of the mirrored surface. A real image is called so because it can be caught on a screen. 2. In a convex mirror, the object and its image lie on the opposite sides of the mirrored surface. The image therefore is a virtual image. It cannot be captured on a screen. 3. In a plane mirror, the image again is a virtual one, as it does not form on the same side as that of the object.

 f = 1/R

A ray parallel to the principal axis, after reflection, will pass through the principal focus in case of a concave mirror or appear to diverge from the principal focus in case of a convex mirror

A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror, after reflection, will emerge parallel to the principal axis

A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror, after reflection, is reflected back along the same path.

A ray incident obliquely to the principal axis, towards a point P, on the concave mirror [Fig. a] or a convex mirror [Fig. (b)], is reflected obliquely. The incident and reflected rays follow the laws of reflection at the point of incidence (point P), making equal angles with the principal axis.

Position of the object Position of the image Nature and size of the image Use At infinityAt the focus Real, inverted and diminished Used by ENT surgeons and dentists

Position of the object Position of the image Nature and size of the image Use Beyond C Between F and C Real, inverted and diminished Used in solar cookers

Position of the object Position of the image Nature and size of the image Use At C Real, inverted and same size as object Used as an erecting mirror in terrestrial telescopes

Position of the object Position of the image Nature and size of the image Use Between the focus and C Beyond C Real, inverted and magnified Used in hospitals to see the internal parts of the body

Position of the object Position of the image Nature and size of the image Use At focusAt infinity Real, inverted and magnified Used in search lights and in head lights of motor cars

Position of the object Position of the image Nature and size of the image Use Between the pole and the focus behind the mirror Virtual, erect and magnified Used as a shaving mirror

 Reflectors in the head lights of cars, search lights in torches etc. to obtain a parallel beam of light. For this, the source of light is placed at the focus of the concave reflector.  By dentist to focus light on the tooth to be examined.  As shaving mirrors and as make-up mirrors to get an enlarged erect image of the face  To concentrate solar radiations in solar heating devices. The food is placed at the focus of a large concave reflector. After reflection, sun light converges on the substance and heats it.

Position of the object Position of the image Nature and size of the image Use At infinityAt the focus Real, inverted and diminished Used by ENT surgeons and dentists Beyond C Between F and C Real, inverted and diminished Used in solar cookers At C Real, inverted and same size as object Used as an erecting mirror in terrestrial telescopes Between the focus and C Beyond C Real, inverted and magnified Used in hospitals to see the internal parts of the body At focusAt infinity Real, inverted and magnified Used in search lights and in head lights of motor cars Between the pole and the focus behind the mirror Virtual, erect and magnified Used as a shaving mirror

Position of the object Position of the image Size of the image Nature of the image At infinity At F, behind the mirror Highly diminished, point-sized Virtual and erect Between infinity and the pole P Between P and F, behind the mirror DiminishedVirtual and erect

Rear-view mirror in an automobile. This convex mirror gives the driver a wider field of view. Reflector in street lamps so as to diverge the light over a large area Uses of Convex Mirror Back to Top Uses of Convex Mirror Back to Top