Curve Mirrors

8/6/2019 Curve Mirrors

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CURVE MIRRORS



CURVE MIRRORS



Key Concepts

y

A curved mirror can be thought of as consisting of a very large number of small plane mirrors oriented atslightly different angles. The laws of reflection alwaysapply, regardless of the shape or smoothness of thesurface.

y A spherical mirror consists of a portion of a sphericalsurface.

y A cylindrical mirror has the shape of a portion of acylinder.

y A converging mirror has a concave reflecting surface. A diverging mirror has a convex reflecting surface.



Terminologies

y The geometric centre of the mirror is calledthe vertex (V ). The centre of a spherical reflectingsurface is called the centre of curvature (C ).

y

The principal axis is a construction line drawn ona ray diagram. The principal axis passes throughthe vertex and the centre of curvature, and isperpendicular to the focal plane.

yThe radius of curvature (R) is the distance fromthe centre of curvature to the mirror.



y The distance between the principal focus (F ) and the vertex is called the focal length ( f )

yThe relationship between the focal length and theradius of curvature is:

y R = 2f

y The principal focus (F ) is a point on the principal axis

on which incident rays parallel to the principal axiseither converge towards, or appear to be diverging from.

y The principal focus can either be real or virtual.

y An axial point is a point lying on the principal axis.

y Paraxial rays are rays which make very small angles with the principal axis and lie close to the axisthroughout the distance between object and image.



Concave mirrors

y are like positive (convex) lenses, in that they bringparallel beams of light together at a single point,called the focal point or focus.

y

or converging mirror, has a reflecting surfacethat bulges inward (away from the incident light).Concave mirrors reflect light inward to one focalpoint. They are used to focus light. Unlike convex

mirrors, concave mirrors show different imagetypes depending on the distance between theobject and the mirror.



y

These mirrors are called "converging" because they tend to collect light that falls on them, refocusingparallel incoming rays toward a focus. This isbecause the light is reflected at different angles,

since the normal to the surface differs with each spoton the mirror.

y Concave mirrors are also like positive lenses in that

they are magnifying mirrors, giving upright images if you look at them from close up, while they give aninverted reflection if you look at them from farenough away.



Concave Mirror



Parts of a Concave Mirror



Convex

mirrors

yare like negative (concave) lenses --they make parallel beams of lightdiverge, and make your reflected imagesmaller. But this makes room withinthe view for reflections of other things,and so they give a "wide angle" view.



Convex mirrorsy A re also called fish eye mirror or diverging

mirror, is a curved mirror in which the reflectivesurface bulges toward the light source. Convex

mirrors reflect light outwards, therefore they arenot used to focus light. Such mirrors always forma virtual image, since the focus (F ) and the centreof curvature ( 2F ) are both imaginary points

"inside" the mirror, which cannot be reached.Therefore images formed by these mirrors cannotbe taken on screen. (As they are inside the mirror)



Reflection of light in a Convex

Mirror





Uses of Curve Mirrors

y Convex mirror lets motorists see around a corner.

y Convex mirrors are used in some automated tellermachines as a simple and handy security feature,

allowing the users to see what is happening behindthem. Similar devices are sold to be attached toordinary computer monitors.

y Some camera phones use convex mirrors to allowthe user to correctly aim the camera while takinga self-portrait.



y Large hospitals, stores and office buildings oftenuse convex mirrors to allow people to see what is

around a corner to help keep people from runninginto one another.

y Convex mirrors are used to make sunglass lenses.These mirrors help reflect some of the sunlightaway from the wearer's eyes.

y Convex mirrors are often found on the passengersides of motor vehicles. These mirrors make

objects appear smaller than they really are. Due tothis compression, these mirrors to reflect a widerimage area, or field of vision.



yConvex mirrors are often placed near ATMsto allow bank customers to see if someone isbehind them. This is a security measure thathelps keep ATM users safe from robbery of any cash withdrawals and helps keep ATM

users' identity more secure.yTwo convex mirrors placed back to back are

used to make a magnifying glass.

yConcave mirrors are used to focus light forheating purposes.



yConcave mirrors have replaced glass lensesin some camera equipment, and enable the

manufacturer to create shorter, more light- weight lenses with greater light-gatheringpower. A disadvantage is that mirror lenses

produce "doughnuts" of light in finishedphotos.

y Just as concave mirrors gather and

concentrate light in camera lenses, they doso in binoculars and telescopes as well,enabling better visibility .

Curve Mirrors

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