Light Study Notes of Physics for MPSC State Exam 2021

By Ganesh Mankar|Updated : September 3rd, 2021

Light Study Notes of Physics for MPSC State Exam 2021: Physics is an important subject for all MPSC exams. The State Service Examination has about six to seven questions on this subject, as well as the MPSC Combine Exam has three to four questions on this component, all the examinations like Police Recruitment, Health Department have questions on Physics. So it is important to study this topic.

Table of Content

Light

aff

Mirror (Spherical)

hr

Concave Mirror

dqa

Convex Mirror

Centre of Curvature

  • The Centre of curvature of a spherical mirror is defined as the centre of the sphere of which the spherical mirror is a part.

Pole (P)

  • The centre point of a spherical mirror is called a pole.

Principal Axis

  • The straight line passing through the pole of the mirror and the centre of curvature is called the Principal Axis.

Focus (F)

  • The principal focus of a spherical mirror is a point on that spherical mirror's principal axis where parallel light rays intersect (meet) or emerge to deviate after reflection.

Focal Length (f)

  • The distance between the Focus and the pole is called the Focal Length.
  • The focal length of any spherical mirror is half its radius. i.e. f= R/2

The radius of curvature (R)

  • The distance between the centre of curvature and the pole is called the Radius of Curvature.
  • The radius is twice the focal length. i.e R = 2f

Sign Convention for Spherical Mirrors

SFFV

 

  • All distances on a spherical mirror are measured from the pole.
  • Objects are placed to the left of the mirror.
  • All distances from the pole to the left are measured Negative.
  • Since the object is always placed to the left, the distance to the object is always Positive.
  • All distances to the left of the spherical mirror are measured Positive.
  • Note-
    • The focal length is measured to the right of the concave mirror, so the focal length is measured Negative.
    • The focal length is measured to the right of the convex mirror, so the focal length is measured Positive.

Lens

ADF

Convex Lens - Converging Action

Ff

Concave Lens - Diverging Action

Centre of curvature (C1, C2 )

  • The centre of curvature of the two spheres of the lens is called the centre of curvatures. In most cases, both are at an equal distance from O.

Principal Axis

  • The straight line passing through both curves is called the principal axis.

Optical Centre

  • The centre point of the lens is called the optical centre.

Principal focus

  • When the incident ray comes parallel to the principal axis and intersects at the point on the principal axis after refracting from the lens, the point is called the Principal focus.

Focal length (f)

  • The distance between the optical centre and the focus is called the focal length.

Sign Convention for lens

eg

  • Any distance in the magnifying glass is measured from the centre of the lens.
  • All distances to the left of the magnifying glass (-ve) are negative, while all distances to the right (+ ve) are considered positive.
  • The object is always placed to the left of the magnifying glass, so the distance to the object is always calculated as Negative.
  • The object is always kept flat, so the height of the object is measured positively.
  • Note:
    • The focal length of a convex lens is positive, as it is measured on the right side.
    • The focal length of the concave lens is negative, as it is measured on the left side.

Reflection

vf

  • When a ray of light passes from one transparent medium to another opaque medium, it returns to the same medium. This property of light is called reflection.
  • The angle of incidence (i) and the angle of reflection (r) are the same. i.e. i=r

Refraction

da

 

  • As light travels from one transparent medium to another, our direction changes. The natural phenomenon of changing this direction is called the refraction of light.
  • The speed of light varies between different media, so the light beam changes its direction as the medium changes.
  • Light is refracted twice through a glass chip.

1st Refraction

  • The first refraction occurs when light rays pass through a sparse medium to a solid medium.
  • When a ray of light passes through a sparse medium to a solid medium, it tends to ‘Normal’.
  • When a ray of light passes through a sparse medium to a solid medium, the angle of incidence is greater than the rate of refraction. In this case, the refractive index of the second medium is higher than the refractive index of the first medium.
  • The higher the refractive index of the second medium, the more the light bends towards the column.

2nd Refraction

  • The second refraction of the glass chip is on the lower part of the glass as the light beam passes through the solid through the sparse medium.
  • When light travels through a solid to a sparse medium, it moves away from ‘Normal’
  • In this case, the angle of refraction is greater than the angle of incidence.
  • In this case, the refractive index of the first medium is higher than the refractive index of the second medium.
  • The higher the value of the refractive index of the first medium, the farther the radiation goes from ‘Normal’.

Refractive Index

  • The rate of change in the direction of light rays varies as they pass through different mediums. They are related to the refractive index of the standard medium.
  • Different media have different refractive indexes, so different media have different directions of light.

Substance

Refractive Index

Air

1.003

Ice

1.31

Water

1.36

Alcohol

1.44

Benzene

1.52

Diamond

2.42

Dispersion:

hh

 

  • Dispersion of light can be defined as the splitting of the light beam (white) into its seven constituent colours when it is passed through any transparent media.
  • Decreasing order of wavelengths: R, O, Y, G, B, I, V
  • Ascending order of frequency: R, O, Y, G, B, I, V

Practice Question

Consider the following statements:

  1. Lightray changes its direction when it passes from one transparent medium to another.
  2. The velocity of light is different in different media.

Select the correct option:

  1. Statement (a) is correct and (b) its correct explanation.
  2. Statements (a) and (b) both are correct but (b) is not its correct explanation.
  3. Statement (a) is correct but (b) is wrong
  4. Statements (a) and (b) both are wrong.

(Give your answer in the comment box)

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Ganesh MankarGanesh MankarMember since Aug 2021
Community Manager for Maharashtra State Exams
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  • The MPSC state service pre-examination consists of about six to seven questions on physics.

  •  The MPSC Combined Prelims Exam consists of three to four questions on the subject of Physics.

  • Eighth, ninth, tenth standard science books should be read for the subject of physics.

  •  Yes! In Maharashtra Police recruitment, there are one to two questions on the subject of Physics.

  • The main examination of MPSC PSI / STI / ASO does not have questions on the subject of Science.

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