Revision: Optics Science SSLC (English Medium) Class 10 Tamil Nadu Board of Secondary Education

Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

The change in the direction of the path of light when it passes from one transparent medium to another transparent medium is called refraction. The refraction of light is essentially a surface phenomenon.

Refracted light is the part of light enters into the other medium and travels in a straight path but in a direction different from its initial direction and is called the refracted light.

Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.

When travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as refraction of light.

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Light changes its direction when going from one transparent medium to another transparent medium. This is called the refraction of light.

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The bending of the light ray from its path in passing from one medium to the other medium is called 'refraction' of light.

A prism is a transparent medium bounded by five plane surfaces with a triangular cross-section.

On passing white light through a prism, the band of colours seen on a screen is called the spectrum.

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The band of the coloured components of a light beam is called its spectrum.

The phenomenon of splitting of white light by a prism into its constituent colours is known as dispersion.

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The splitting of light into its component colours is called dispersion.

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The process of separation of light into its component colours while passing through a medium is called the dispersion of light.

The phenomenon of the splitting of white light by a prism into its constituent colours is known as dispersion of light.

When a beam of white light or composite light is refracted through any transparent media such as glass or water, it is split into its component colours. This phenomenon is called ‘dispersion of light’.

Scattering is the process of absorption and then re-emission of light energy by the dust particles and air molecules present in the atmosphere.

The imaginary line passing through both centres of curvature is called the principal axis of the lens.

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The line joining the centres of curvature of the surfaces of the lens is called the 'principal axis' of the lens.

A lens which bulges out in the middle, is a convex lens. A light beam converges on passing through such a lens, so it is also called a converging lens.

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The lens which has two spherical surfaces which are puffed up outwards is called a convex or double convex lens.

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The lenses which are thicker in the middle and thinner at the edges, are called 'convex lenses'.

A lens which is bent inwards in the middle is a concave lens. Such a lens diverges the light rays incident on it, so it is also called a diverging lens.

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This lens is thicker near the centre as compared to the edges. The lens with both surfaces spherical on the inside is called a concave or double concave lens.

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The lenses which are thinner in the middle and thicker at the edges, are called 'concave lenses'.

The centres of spheres whose parts form surfaces of the lenses are called centres of curvatures of the lenses.

The radii (R₁ and R₂) of the spheres whose parts form surfaces of the lenses are called the radii of curvature of the lens.

The point inside a lens on the principal axis, through which light rays pass without changing their path is called the optical centre of a lens.

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The point on the principal axis of a lens such that a ray of light directed towards it emerges from the lens in the same direction, without deviation.

Principal focus (F) is the point on the principal axis at which light rays parallel to the principal axis converge after passing through a convex lens.

The distance between the optical centre and principal focus of a lens is called its focal length.

A lens is a transparent refracting medium bounded by either two spherical surfaces, or one spherical surface and the other surface plane.

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A lens is a transparent medium bound by two surfaces.

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A lens is a transparent medium (such as glass) bounded by two curved surfaces or one curved and one plane surface.

For a convex lens, the first focal point is a point F₁ on the principal axis of the lens such that the rays of light coming from it, after refraction through the lens, becomes parallel to the principal axis of the lens.

The focus of a lens (often called the principal focus) is a specific point on its principal axis where light rays parallel to the axis either converge or appear to originate from after passing through the lens.

For a concave lens, second focal point is a point F₂ on the principal axis of the lens such that the rays of light incident parallel to the principal axis, after refraction from the lens, appear to be diverging from this point.

The centre of the sphere, whose part is the lens surface, is called the centre of curvature of that surface of the lens.

The radius of the sphere, whose part is the lens surface, is called the radius of curvature of that surface of the lens.

It is the line joining the centres of curvature of the two surfaces of the lens.

It is a point on the principal axis of the lens such that a ray of light directed towards this point emerges parallel to its direction of incidence.

For a concave lens, the first focal point is a point F₁ on the principal axis of the lens such that the incident rays of light appearing to meet at it, q,fter refraction from the lens become parallel to the principal axis of the lens.

A plane normal to the principal axis, passing through the focus, is called the focal plane.

A plane passing through the first focal point and normal to the principal axis of the lens, is called the first focal plane.

A plane passing through the second focal point and normal to the principal axis of the lens, is called the second focal plane.

The distance of focus (or focal point) from the optical centre of a lens, is called its focal length.

The distance from the optical centre O of the lens to its first focal point F₁ is called the first focal length Ji of the lens.

The distance from the optical centre 0 of the lens to the second focal point F₂ is called the second focal length f₂ of the lens.

For a convex lens, the second focal point is a point F₂ on the principal axis of the lens such that the rays of light incident parallel to the principal axis, after refraction from the lens, pass through it.

For a convex lens, the principal focus is a point on the principal axis of a convex lens at which the rays of light originally parallel and close to the principal axis of the lens pass through it after refraction by the lens.

It is the line joining the centers of curvature of the two surfaces of the lens.

For a concave lens, the principal focus is a point on its principal axis at which the rays of light originally parallel to the principal axis, appear to come from it after refraction by the lens.

The deviation of the incident light rays produced by a lens on refraction through it, is a measure of its power.

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The power of a lens is defined as the reciprocal of its focal length. It is represented by the letter P.

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The power (P) of a thin lens is equal to the reciprocal of its focal length (f) measured in metres.

Power of a lens is defined as the ability of a lens to bend the rays of light. It is given by the reciprocal of focal length in metre.

The power of a lens is a measure of the deviation produced by it in the path of rays refracted through it.

Magnification (m) = \[\frac{\text{Height of the Image}}{\text{Height of the object}}=\frac{h^{\prime}}{h}\]

Magnification in terms of object and image distances:

Magnification (m ) = \[\frac {h'}{h}\] = \[\frac {v}{u}\]

\[\frac {1}{v}\] - \[\frac {1}{u}\] = \[\frac {1}{f}\]

Power of lens (in D) = \[\frac{1}{\text{focal length (in metre)}}\]

or

P = \[\frac {1}{f}\]

or

P = \[\frac {1}{f (m)}\]

Power of a Lens in a Medium:

P = (n₂ - n₁)\[\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)\] = \[\frac {n_1}{f}\]

• Dispersion is the splitting of white light into seven colours (VIBGYOR) when it passes through a prism or similar transparent medium.
• Human eyes can detect light with wavelengths ranging from 400 nm (violet) to 700 nm (red).
• Different colours travel at different speeds in a medium like glass, so each colour has a different refractive index.
• Violet light bends the most, and red light bends the least, as it passes through a prism, producing a spectrum.
• A rainbow is formed due to dispersion, refraction, and internal reflection of sunlight by raindrops acting as tiny prisms.

• Shorter wavelengths (violet and blue) are scattered more than longer wavelengths (red).
• The intensity of scattering follows Rayleigh’s law:
  I ∝ \[\frac {1}{λ^4}\]​
• Very small particles (smaller than the wavelength of light) scatter light more effectively than larger particles.
• The sky appears blue because blue light is scattered more due to its shorter wavelength.
• Red light scatters least, causing red/orange sunsets and making sunlight near Earth richer in red light.

• Lenses are widely used in daily life, such as in spectacles, peepholes, magnifiers, and telescopes.
• Light passing through a lens undergoes refraction twice: once on entering and once on exiting the lens.
• The shape of a lens affects the direction of light; convex lenses converge light, while concave lenses diverge it.
• Most lenses have surfaces that are parts of spheres, with common types including biconvex, biconcave, plano-convex, and meniscus lenses.

• Pole (mirror) or optical centre (lens) is the origin; principal axis is the X-axis.
• Distances to the right are positive, to the left are negative; heights above the axis are positive, below are negative.
• Concave mirror: $f$ and R are negative; Convex mirror: $f$ and R are positive.
• Real images: image distance and magnification are negative; Virtual images: both are positive.
• Lenses are always negative; they are positive for real images and negative for virtual images; they are positive for convex lenses and negative for concave lenses.

• Myopia is a vision defect in which distant objects appear blurry, while near objects are seen clearly.
• This occurs because the image of distant objects forms on the retina.
• The far point is not at infinity but is shifted closer to the eye.
• Causes include increased curvature of the cornea/lens or elongation of the eyeball.
• Corrected using a concave lens of negative power, which diverges light rays to focus the image on the retina.

• Presbyopia is an age-related vision defect where the eye’s ability to focus on nearby objects decreases.
• It is caused by weakened ciliary muscles and reduced flexibility of the eye lens.
• The near point shifts farther, making close-up vision difficult.
• Bifocal lenses are commonly used for correction—concave at the top (for myopia) and convex at the bottom (for hypermetropia).
• It can also be corrected with contact lenses or, in some cases, surgery.