Note on Mirror

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A mirror is an object that reflects light in such a way that you can see your image in it whether real or virtual, erect or inverted and diminished or enlarged. Plane mirrors are the common mirrors used in our home. This is different from other light-reflecting objects that does not preserve much of the original wave signal other than colour and diffuse reflected light.

Types of mirror

There are two types of mirror they are:

  1. plane mirror
  2. spherical mirror

Plane mirror

A plane mirror is a mirror with a flat refractive surface. We use the plane mirror as a looking glass. Plane mirrors are the only type of mirrors for which a real object always produces an image that is virtual, erect and of the same size as the object.

Spherical mirror

A mirror whose polished, reflecting surface is a part of a hollow sphere of glass, is called a spherical mirror. One side of it is made opaque and another side acts as a reflecting surface.

Depending on the nature of the reflecting surface of the mirror, the mirrors are of two types:

1. Concave mirror

A mirror which is a part of the sphere and is polished from the outer surface such as its reflecting side is inward is called a concave mirror. In this mirror, parallel rays of light converge at a point after reflection. A concave mirror is used to convert solar energy into heat energy, in torches and car's headlights to reflect the light of the bulb to form a powerful beam of light, in an astronomical telescope to view stars and planets.

Uses of Concave mirror

  1. Concave mirrors are used as shaving glass.
  2. Concave mirrors are used as reflectors in car headlights, searchlights, torches, etc.
  3. Concave mirrors are used in projectors and telescopes.
  4. Concave mirrors are used to observe the ear and nose of patients.

2.Convex mirror

A mirror which is a part of the sphere and is silver polished from the inner surface such as its reflecting side is outward is called a convex mirror. In this mirror, parallel rays of light diverge after reflection. An image formed in the convex mirror is always virtual, erect and diminished. The convex mirror is used as rear view mirrors in cars, motorcycle, scooters, trucks, etc.

Uses of Convex mirror

  1. The convex mirrors are used in cars that give the clear view of the vehicles approaching from behind.
  2. It can diverge the light over a larger area and, therefore, it is used as a street light reflector.

Differences between Concave and Convex mirror

Concave mirror Convex mirror
A spherical mirror whose inner hollow surface is the reflecting surface is called a concave mirror. A spherical mirror whose outer bulging surface is the reflecting surface is called a convex mirror.
It may give magnified or diminished image. It forms diminished image (smaller in size only).
The image formed is real except when the object is between focus and principal. The image formed is always virtual.

Terms used in spherical mirror:

1. Pole: It is a geometrical centre of the surface of a mirror. It is represented by a point P.

2. Center of Curvature: It is the centre of the hollow sphere of which mirror is a part, represented by C.

3. The radius of Curvature: It is the radius of the hollow sphere of which mirror is a part, denoted by R.

4. Principal axis: The line joining the pole of the mirror and the centre of curvature and produced on both sides is called the principal axis.

5. Principal focus: The point on the principal axis where a beam of light incident to spherical mirror parallel to the principal axis converges or appears to be diverging from after reflection, is called the principal focus. It is denoted by the letter F. The principal focus is real in the concave mirror and virtual in the case of a convex mirror.

6. Focal length: It is the distance between principal focus and pole of the mirror. It is denoted by f. The focal length is half of the radius of curvature.

Rules Used to Draw Diagrams in Concave mirror:

  1. An incident ray passing parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection.
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  2. An incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.
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  3. An incident ray passing through the centre of curvature reflects back in the same direction.
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Ray diagram for Concave Mirror

  1. If an object is at infinity from the mirror then the image of the mirror forms in the focal point.
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  2. If an object is kept beyond the centre of curvature then image forms in between the centre of curvature and focus.
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Rules Used to Draw Diagrams in Convex mirror

  1. An incident ray travelling parallel to the principal axis on the way to a convex mirror will reflect in such a manner that its extension will pass through the focal point.
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  2. In the convex mirror, focal point and centre of curvature lie in the backside or reflecting the surface of a mirror.
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  3. An incident ray passing through the centre of curvature reflects back in the same direction.
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Ray diagram for Convex Mirror

  1. If an object is kept at infinity then the image of an object is formed at the focal point of the reflecting surface. Such images are virtual, erect and diminished.
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  2. If an object is kept between the pole of mirror and infinity then the image is formed between the pole of the mirror and focal point. Such images are Virtual, erect and diminished.
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Sign convention for spherical mirrors

  1. All distances are measured from the pole of the mirror.
  2. Distances measured in the direction of the incident ray are positive.
  3. Distances measured in the direction opposite to that of the incident rays are negative.
  4. Distances measured below the principal axis are the negative i.e. height of a real inverted.
  5. Distances measured from the principal axis are positive, i.e. heights of an erect image are positive.

  • A mirror whose polished, reflecting surface is a part of hollow sphere of glass, is called a spherical mirror. One side of it is made opaque and another side acts as a reflecting surface.
  • Concave mirror : A mirror which is a part of sphere and is polished from the outer surface such that its reflecting side is inward is called a concave mirror.
  • Convex mirror : A mirror which is a part of sphere and is silver polished from the inner surface such that its reflecting side is outward is called a convex mirror.
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Very Short Questions

A mirror whose polished, reflecting surface is a part of a hollow sphere of glass is called a spherical mirror.

A spherical mirror whose outer surface is reflecting surface is called a convex mirror.

A spherical mirror whose inner surface is reflecting surface is called a convex mirror.

A concave mirror is also called converging mirror because a parallel beam of light incident on it, converges to a point after reflection.

Convex mirror is also called a diverging mirror because a parallel beam of light incident on it, appears to be diverging from a point after reflection.

0%
  • If an incident ray passes through the centre of curvature of a spherical mirror, the reflected ray will _______.

    pass through the focus


    pass between the centre of focus and pole


    pass through the pole


    move in the same path


  • An image formed by a convex mirror is always ______.

    virtual, real and magnified


    real, erect and magnified


    real, inverted and diminished


    virtual, erect and diminished


  • The energy that gives us sensation of sight is called ______.

    potential energy
    electrical energy
    mechanical energy
    light energy
  • The individual unit of light is called ______.

    gluon


    photon


    atom


    beam


  • Path of a light beam is ______.

    parallel to the ground


    curved


    depends on medium


    sometimes straight sometimes curved


  •  A light beam can be _______.

    refracted


    all of the answers are right


    sometimes straight sometimes curved


    reflected


  • The spherical mirror whose inner surface is reflective is called ______.

    reflective mirror


    plain mirror


    convex mirror


    concave mirror


  • The concave mirror is also called ______.

    diverging mirror


    both


    converging mirror


    none


  • Convex mirror is also called ______.

    both answers are right


    conversing mirror


    diverging mirror


    none are right


  • The image formed by a concave mirror is ______.

    real


    depends on where it is placed


    bigger


    erect


  • The image formed by convex mirror is ______.

    all of the above answers are right


    inverted


    real


    smaller than object


  • In concave mirror what is the location of the image formed when an object is at infinity?

    at the principal focus


    in between center of curvature and principal focus


    at the center of curvature


    beyond center of curvature


  • In concave mirror what is the location of the image formed when an object is in between infinity and C?

    at the principal focus


    in between center of curvature and principal focus


    at the center of curvature


    beyond center of curvature


  • In concave mirror what is the location of image formed when object is at center of curvature ?

    in between center of curvature and principal focus


    at the principal focus


    beyond center of curvature


    at the center of curvature


  • What is the size of the image when the object is placed at the center of curvature of concave mirror?

    larger than object


    same size of the object


    incomplete information to deduce the answer


    smaller than object


  • The reason for using convex mirror in cars is because ______.

    convex mirror forms bigger image so it is easier see the object


    convex mirror has narrow field of view so it is easier to focus on traffic


    all of the answers are correct


    convex mirror always form an erect image so easy identification of object


  • Light is a form of energy produced by a ______.

    transparent object


    luminous object


    opaque object


    non-luminous object


  • An example for non-luminous object is ______.

    an electric bulb


    the sun


    a candle


    the moon


  • The phenomenon by which the incident light falling on a surface is sent back into the same medium is known as ______.

    Refraction


    Polarization


    reflection


    Absorption


  • When light is incident on a polished surface ______ reflection takes place.

    irregular


    normal


    diffused


    regular


  • An object becomes invisible when it undergoes ______reflection.

    irregular


    diffused


    regular


    normal


  • The image formed by a plane mirror is  ______.

    real or virtual


    real and inverted


    real and erect


    virtual and inverted


  • The centre of the sphere of which the spherical mirror forms a part is called ______.

    vertex


    pole


    centre of curvature


    focus


  • The focus of a concave mirror is _______.

    virtual


    undefined


    Real


    at the pole


  • A converging mirror is known as ______.

    plane mirror


    cylindrical mirror


    convex mirror


    concave mirror


  • Radius of curvature of a concave mirror is always ______ to the mirror.

    perpendicular


    inclined at 45o


    Parallel


    inclined at 60o


  • If the image formed by a concave mirror is virtual, erect and magnified, then the object is placed

    beyond the centre of curvature
    at the focus
    between the pole of the mirror and the focus
    at the centre of curvature
  • Dentists use a _____________ to focus light on the tooth of a patient.

    plane mirror
    convex mirror
    cylindrical mirror
    concave mirror
  • An object is placed 1.5 m from a plane mirror. How far is the image from the person?

    1.5 m
    3 m
    1 m
    2 m
  • An object placed 2m from a plane mirror is shifted by 0.5 m away from the mirror. What is the distance between the object and its image?

    2 m
    5 m
    3 m
    1.5 m
  • What is the angle between the incident and reflected rays when a ray of light is incident normally on a plane mirror?

    180o
    45o
    0o
    90o
  • Name the type of image that can be obtained on a screen.

    Converging
    virtual
    Real
    Diverging
  • A ray of light is incident on a plane mirror and the angle of incidence is 25o. What is the angle of reflection?

    25o


    90o


    00


    50o


  • A ray of light is incident on a plane mirror and the angle of reflection is 50o. Calculate the angle between the incident ray and the reflected ray.

    25o


    50o


    90o


    100o


  • Which of the following is used to make a periscope?

    Lens
    Plane mirror
    Convex mirror
    Concave mirror
  • Which mirror has a wider field of view?

    Plane mirror
    Convex mirror
    Cylindrical mirror
    Concave mirror
  • The focal length of a concave mirror is 15 cm. What is its radius of curvature?

    15 cm
    7.5 cm
    45 cm
    30 cm
  • A ray of light passing through the ______ retraces its path.

    vertex


    centre of curvature


    Focus


    Pole


  • When an object is placed at the focus of a concave mirror, the image will be formed at ______.

    pole


    infinity


    focus


    centre of curvature


  • Butter paper is an example for ______ object.

    a transparent


    an opaque


    a luminous


    a translucent


  • An object of size 2.0 cm is placed perpendicular to the principal axis of a concave mirror. The distance of the object from the mirror equals to the radius of curvature. The size of the image will be ______.

    1.0 cm


    0.5 cm


    1.5 cm


    2.0 cm


  • If an incident ray passes through the centre of curvature of a spherical mirror, the reflected ray will ______.

    pass through the centre of curvature


    pass through the focus


    retrace its path


    pass through the pole


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DISCUSSIONS ABOUT THIS NOTE

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keshab dayal

why dose the sun appare larger at sunrise


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Anurag sah

if object lies between F and C ,which type of image is formed?


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conditions required for

Condition require for reflection of light


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SHIVA KORI

Why Concave mirror is used in torch light as a reflactor ?


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