Reflection - Physics Notes | EduRev

Current Affairs & General Knowledge

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Relection

  • The phenomenon due to which a beam of light, travelling through a certain medium, on striking some surface, bounce off from it in some other direction is called reflection of light.

Laws of reflection:

  1. The incident ray, the reflection ray and the normal at the point of incident lie in the same plane.
  2. Angle of incidence is always equal to angle of reflection.

Reflection - Physics Notes | EduRev

  1. When the two mirrors are placed at certain angle to each other then number of images formed will be,
                    n = (360 / Ø)-1 

Reflection - Physics Notes | EduRev

  1. The least size of the mirror required is half the height of the observer

Reflection - Physics Notes | EduRev

Characteristics of image

  • If the image is erect and of the same size as the object and it appears to be formed behind the mirror, the reflecting surface is plane.
  • If the image is erect and formed behind the mirror but diminished in size for all positions of the mirror, the mirror must be convex.
  • If the image is erect, formed behind the mirror and enlarged, then the mirror is concave.

 

Reflection in a concave & convex mirror

Reflection - Physics Notes | EduRev

Reflection - Physics Notes | EduRev

 

Reflection - Physics Notes | EduRev

 

Reflection - Physics Notes | EduRev
Reflection - Physics Notes | EduRev

 

Position of the object

Position of the image

Size of the image

Nature of the image

At infinity

At the focus F

Highly diminished, point-sized

Real and inverted

Beyond C

Between F and C

Diminished

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 erect

 

Uses of concave mirrors

  • Concave mirrors are commonly used in torches, search-lights and vehicles headlights to get powerful parallel beams of light.
  • They are often used as shaving mirrors to see a larger image of the face.
  • The dentists use concave mirrors to see large images of the teeth of patients.
  • Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Images by convex mirrors

Position of the object

Position of the image

Size of the image

Nature of the image

At infinity

At the focus F, behind the mirror

Highly diminished, point-sized

Virtual and erect

Between infinity and the pole P of the mirror

Between P and F, behind the mirror

Diminished

Virtual and erect

 

 Refraction at a Plane Surface 

  • When a ray of light passes from one medium to other it suffers a change in direction at the boundary of separation of two media.
  • This phenomenon is called refraction.
  • When a ray of light travels from one medium to another the wavelength and velocity of light change but the frequency does not change.

Reflection - Physics Notes | EduRev

Refraction by Spherical Lenses

Reflection - Physics Notes | EduRev
Reflection - Physics Notes | EduRev

 Image Formation by convex Lenses

 

Position of the object

Position of the image

Relative size of the image

Nature of the image

At infinity

At focus F2 

Highly diminished, point-sized

Real and inverted

Beyond 2F1 

Between F2 and 2F2 

Diminished

Real and inverted

At 2F1 

At 2F2 

Same size

Real and inverted

Between F1 and 2F1 

Beyond 2F2 

Enlarged

Real and inverted

At focus F1 

At infinity

Infinitely large or highly enlarged

Real and inverted

Between focus F1and optical centre O

On the same side of the lens as the object

Enlarged

Virtual and erect

Position of the object

Position of the image

Relative size of the image

Nature of the image

At infinity

At focus F1

Highly diminished, point-sized

Virtual and erect

Between infinity and optical centre O of the lens

Between focus F1 and optical centre O

Diminished

Virtual and erect

 

Optical Instruments Physics

  • Telescopes and microscopes are the aids to increase the apparent size of objects by increasing visual angle.
  • Very distant objects (such as sun and moon), although very big in size appear very small because they subtend very small visual angle at the eye.
  • To see them bigger, we cannot decrease their distance.
  • But if with the help of proper lenses, a small image of the distant object be formed close to the eye then its image will subtend a large visual angle at the eye and the object will appear large. Telescope is based on this principle.
  • Very small objects subtend small visual angle due to their smallness.
  • We can increase the visual angle by bringing these objects closer to the eye, but we cannot do so beyond a certain limit (25cm) because then the objects will not be seen distinct.
  • If with the help of proper lenses, a large image of small object is formed, then this image will subtend a large visual angle at the eye and the object will appear large. Microscope is based on this principle.
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