NEET Physics Ray Optics and Optical Instruments Notes

NEET Physics Ray Optics and Optical Instruments Notes

Ray Optics And Optical Instruments

Laws of Reflection of Light:

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

\(\text { i.e., }\lfloor i=\lfloor r\)

NEET Physics Ray Optics Important Formulas

Sign conventions:

• All distances are measured from the pole of the mirror.
• Distances measured in the direction of incident light are taken positively and vice versa.
• Heights measured upward and perpendicular to the principal axis are taken positively and vice versa.

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For a spherical mirror, the relation between focal length and radius of curvature is,

\(\mathrm{f}=\frac{\mathrm{R}}{2}\)

Where f is the focal length and ‘R’ is the radius of curvature of the mirror.

Mirror equation

\(\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)

Where u is the object distance and v is the image distance.

Linear magnification is the ratio of the height of the image to the height of the object.

\(\mathrm{m}=\frac{\mathrm{h}_{\mathrm{i}}}{\mathrm{h}_{\mathrm{o}}}\)

For a spherical mirror, \(\mathrm{m}=-\frac{\mathrm{v}}{\mathrm{u}}\)

Best Short Notes for Ray Optics and Optical Instruments NEET

The refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light of medium (v)

\(\mathrm{n}=\frac{\mathrm{e}}{\mathrm{v}}\)

Refractive index of a medium depends on the wavelength of light used.

Longer the wavelength smaller is the refractive index.

NEET Physics Ray Optics and Optical Instruments Notes

Laws Of Refraction Of Llight

1. The incident ray, refracted ray and the normal drawn at the point of incidence all lie in the same plane.
2. Sine of angle of incidence to the sine of angle of refraction is a constant for a given pair of media and for given wavelength of light.

\(\text { i.e., } \frac{\sin i}{\sin r}=\text { constant }=n_{21}\)

Where is the refractive index of medium 2 w.r.to medium 1.

If \(n_{21}>1, \mathrm{r}<\mathrm{i} \text { and if } n_{21}<1, \mathrm{r}>\mathrm{i}\)

Expression for normal shift

N. S .= \(t\left(1-\frac{1}{n}\right)\)

where t is the thickness and n is the refractive index of the medium.

Relation between refractive index and critical angle

\(\sin \mathrm{C}=\mathrm{n}_{21}=\frac{\mathrm{n}_2}{\mathrm{n}_1}\)

Where ‘C’ is the critical angle

Relation between n, u, v, and R for a spherical refracting surface.

\(\frac{\mathrm{n}_2}{\mathrm{v}}-\frac{\mathrm{n}_1}{\mathrm{u}}=\frac{\mathrm{n}_2-\mathrm{n}_1}{\mathrm{R}}\)

Where, n₂ is the refractive index of the image medium.

n₁ is the refractive index of the object medium.

And R is the radius of curvature.

Lens maker’s formula

\(\frac{1}{\mathrm{f}}=\left(\mathrm{n}_{21}-1\right)\left(\frac{1}{\mathrm{R}_1}-\frac{1}{\mathrm{R}_2}\right)\)

Thin lens formula

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

Magnification produced by a lens

\(\mathrm{m}=\frac{\mathrm{v}}{\mathrm{u}}\)

Ray Optics and Optical Instruments NEET Important Questions and Answers

Power of a lens

\(P=\frac{1}{f}\)

The S.I. unit of power of a lens is dioptre (D)

1D = 1m¯¹

Combination of thin lenses in contact

In terms of power,

P_eff = P₁ + P₂ + P₃ + ….

In terms of magnification,

M_eff = m₁. m₂ . m₃…..

Refraction through a prism

At the angle of minimum deviation

\(\begin{aligned}
& \delta=\mathrm{D}_{\mathrm{m}}, \mathrm{i}=\mathrm{e} \Rightarrow r_{\mathrm{i}}=r_2 \\
& \Rightarrow \mathrm{r}=\frac{\mathrm{A}}{2} \\
& \mathrm{D}=\frac{\left(\mathrm{A}+\mathrm{D}_{\mathrm{m}}\right)}{2} \\
& \mathrm{n}_{21}=\frac{\mathrm{n}_2}{\mathrm{n}_1}=\frac{\sin \left(\frac{\left(\mathrm{A}+\mathrm{D}_{\mathrm{m}}\right)}{2}\right)}{\sin \left(\frac{\mathrm{A}}{2}\right)}
\end{aligned}\)

For a small-angle prism,

\(\begin{aligned}
& \mathrm{n}_{21}=\frac{\frac{\left(\mathrm{A}+\mathrm{D}_{\mathrm{m}}\right)}{2}}{\left(\frac{\mathrm{A}}{2}\right)} \\
& \& \mathrm{D}_{\mathrm{m}}=\left(n_{21}-1\right) \mathrm{A}
\end{aligned}\)

NEET Physics Ray Optics and Optical Instruments MCQs with Solutions

Ray Optics

In the above set of equations, i is the angle of incidence, e is the angle of emergence, A isthe  angle of prism & are angle of refractions at two boundaries, is deviation and Dm is the angle of minimum deviation.

According to Rayleigh’s law of scattering if the particle size is greater the then,

Scattering is proportional to \(\frac{1}{\lambda^4}\).

The standard value of the near point of the human eye is D = 25 cm.

Magnification is produced by a simple microscope when the image is produced at a near point,

When the image is formed at infinity,

\(m=\frac{D}{f}\)

Magnification produced by a compound microscope when image is formed at infinity is,

\(\begin{aligned}
& m=m_0 m_e \\
& m=\left(\frac{L}{f_0}\right)\left(\frac{D}{f_e}\right)
\end{aligned}\)

Magnification produced by a compound microscope when image is formed at near point is,

Reflection and Refraction of Light NEET Notes

Ray Optics

Where, and are the magnification of the objective and eyepiece respectively fo and fe are the focal lengths of the objective and the eyepiece respectively.

Magnification of the telescope is given by,

\(m=\frac{f_o}{f_o}\)

NEET Study Material for Ray Optics and Optical Instruments Chapter

where fo and fe are the focal lengths of the objective and eyepiece respectively.

The magnifying power of a telescope is the ratio of the angle subtended at the eye by the image to the angle subtended at the eye by the object

\(\text { i.e., } \mathrm{m}=\frac{\beta}{\alpha}\)