# JEE Main

Explore popular questions from Optics for JEE Main. This collection covers Optics previous year JEE Main questions hand picked by experienced teachers.

## Mathematics

Optics

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Q 1. A concave mirror of focal length {tex} f {/tex} produces an image {tex} n {/tex} times the size of the object. If the image is real then the distance of the object from the mirror is

A

{tex} ( n - 1 ) f {/tex}

B

{tex} \frac { ( n - 1 ) } { n } f {/tex}

{tex} \frac { ( n + 1 ) } { n } f {/tex}

D

{tex} ( n + 1 ) f {/tex}

##### Explanation

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Q 2. A spherical surface of radius of curvature {tex} R {/tex} separates air (refractive index 1.0{tex} ) {/tex} from glass (refractive index 1.5.) The centre of curvature is in the glass. A point object {tex} P {/tex} placed in air is found to have a real image {tex} Q {/tex} in the glass. The line {tex} P Q {/tex} cuts the surface at a point {tex} O {/tex}, and {tex} P O = O Q . {/tex} The distance {tex} P O {/tex} is equal to

5{tex} R {/tex}

B

3{tex} R {/tex}

C

2{tex} R {/tex}

D

1.5{tex} R {/tex}

##### Explanation

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Q 3. A ray of light falls normally on a refracting face of a prism of refractive index {tex} 1.5 . {/tex} If the ray just fails to emerge from the prism. Then the angle of prism is

{tex} \sin ^ { - 1 } \left( \frac { 2 } { 3 } \right) {/tex}

B

{tex} \cos ^ { - 1 } \left( \frac { 2 } { 3 } \right) {/tex}

C

{tex} \sin ^ { - 1 } \left( \frac { 1 } { 2 } \right) {/tex}

D

{tex} \sin ^ { - 1 } \left( \frac { 1 } { 3 } \right) {/tex}

##### Explanation

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Q 4. A ray of light passes through four transparent media with refractive indices {tex} \mu _ { 1 } , \mu _ { 2 } , \mu _ { 3 } , {/tex} and {tex} \mu _ { 4 } {/tex} as shown in the Fig. The surfaces of all media are parallel. If the emergent ray {tex} C D {/tex} is parallel to the incident ray {tex} A B , {/tex} then

A

{tex} \mu _ { 1 } = \mu _ { 2 } {/tex}

B

{tex} \mu _ { 2 } = \mu _ { 3 } {/tex}

C

{tex} \mu _ { 3 } = \mu _ { 4 } {/tex}

{tex} \mu _ { 4 } = \mu _ { 1 } {/tex}

##### Explanation

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Q 5. Two plane mirrors {tex} A {/tex} and {tex} B {/tex} are aligned parallel to each other as shown in Fig. A light ray is incident at an angle of {tex} 30 ^ { \circ } {/tex} at a point just inside one end of {tex} A {/tex}. The plane of incidence coincides with the plane of the Fig. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is

A

28

30

C

32

D

34

##### Explanation

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Q 6. An object 1{tex} \mathrm { cm } {/tex} tall is placed in front of a mirror at a distance of 4{tex} \mathrm { cm } . {/tex} In order to produce an upright image of 3{tex} \mathrm { cm } {/tex} height, one needs a

A

convex mirror of radius of curvature {tex} 12 \mathrm { cm } . {/tex}

concave mirror of radius of curvature {tex} 12 \mathrm { cm } . {/tex}

C

concave mirror of radius of curvature {tex} 4 \mathrm { cm } . {/tex}

D

plane mirror of height {tex} 12 \mathrm { cm } . {/tex}

##### Explanation

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Q 7. Light travels through a glass plate of thickness {tex} t {/tex} and having refractive index {tex} \mu {/tex}. If {tex} c {/tex} be the velocity of light in vacuum, the time taken by the light to travel this thickness of glass is

A

{tex} \frac { t } { \mu c } {/tex}

B

{tex} t \mu c {/tex}

{tex} \frac { \mu t } { c } {/tex}

D

{tex} \frac { t c } { \mu } {/tex}

##### Explanation

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Q 8. A ray of light strikes a glass plate at an angle of {tex} 60 ^ { \circ } {/tex} with the vertical. If the reflected and refracted rays are perpendicular to each other, the refractive index of glass is

A

{tex} \frac { \sqrt { 3 } } { 2 } {/tex}

B

{tex} \frac { 3 } { 2 } {/tex}

C

{tex} \frac { 1 } { 2 } {/tex}

{tex} \sqrt { 3 } {/tex}

##### Explanation

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Q 9. An optically active compound

Rotates the plane polarized light

B

Changes the direction of polarized light

C

Do not allow plane polarized light to pass through

D

None of the above

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Q 10. The principle of optical fibre is

A

Diffraction

B

Polarization

C

Interference

Total internal reflection

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Q 11. A beam of light starting from point {tex} A {/tex} reflects from a mirror {tex} M {/tex} and forms an image at {tex} B {/tex} as shown in the same horizontal plane as {tex} A {/tex}. For small angle of incidence {tex} i , A B {/tex} is equal to

A

{tex} i D {/tex}

2{tex} i D {/tex}

C

4{tex} i D {/tex}

D

{tex} i D / 2 {/tex}

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Q 12. In Young's double slit experiment, the width of one slit is double that of the other. The ratio of intensity of a bright band to that of a dark band in the interference pattern will be

A

{tex} 2 : 1 {/tex}

B

{tex} 3 : 1 {/tex}

C

{tex} 6 : 1 {/tex}

{tex} 9 : 1 {/tex}

##### Explanation

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Q 13. The critical angle of a medium is {tex} \sin ^ { - 1 } ( 3 / 5 ) . {/tex} The polarizing angle of the medium will be

A

{tex} \sin ^ { - 1 } ( 4 / 5 ) {/tex}

{tex} \tan ^ { - 1 } ( 5 / 3 ) {/tex}

C

{tex} \tan ^ { - 1 } ( 3 / 4 ) {/tex}

D

{tex} \tan ^ { - 1 } ( 4 / 3 ) {/tex}

##### Explanation

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Q 14. A glass prism of refractive index {tex}1.5{/tex} is immersed in water {tex} ( \mu = 4 / 3 ) . {/tex} A light beam incident normally on the face {tex} A B {/tex} is totally reflected to reach the face {tex} B C , {/tex} if

{tex} \sin \theta \geq \frac { 8 } { 9 } {/tex}

B

{tex} \sin \theta \leq \frac { 2 } { 3 } {/tex}

C

{tex} \sin \theta = \frac { 4 } { 5 } {/tex}

D

{tex} \frac { 2 } { 3 } < \sin \theta < \frac { 8 } { 9 } {/tex}

##### Explanation

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Q 15. An object is placed at a distance of 3{tex} f {/tex} from a convex lens of focal length {tex} f . {/tex} A slab of refractive index {tex} \mu {/tex} is placed in between lens and object. The image of the object will be formed nearest to the object if thickness of the slab is

A

{tex} f {/tex}

B

2{tex} f {/tex}

C

{tex} \frac { f } { \mu - 1 } {/tex}

{tex} \frac { \mu f } { \mu - 1 } {/tex}

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Q 16. A ray of light falls on a prism {tex} A B C ( A B = B C ) {/tex} and travels as shown in Fig. The refractive index of the prism material should be greater than

A

4{tex} / 3 {/tex}

{tex} \sqrt { 2 } {/tex}

C

{tex} 1.5 {/tex}

D

{tex} \sqrt { 3 } {/tex}

##### Explanation

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Q 17. On introducing a thin sheet of mica (thickness {tex} 12 \times {/tex} {tex} 10 ^ { - 5 } \mathrm { cm } {/tex} ) in path of one of the interfering beams in Young's double slit experiment, the central fringe is shifted through a distance equal to the spacing between successive bright fringes. The refractive index of mica is (wavelength of light used {tex} \lambda = 6 \times 10 ^ { - 5 } \mathrm { cm } {/tex} )

A

{tex} 1.33 {/tex}

{tex} 1.5 {/tex}

C

{tex}2.5{/tex}

D

{tex}1.478{/tex}

##### Explanation

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Q 18. Focal length of an equiconvex lens is {tex} 20 \mathrm { cm } . {/tex} If we cut it once perpendicular to principle axis, and then along principal axis, then focal length of each part will be

A

20{tex} \mathrm { cm } {/tex}

B

10{tex} \mathrm { cm } {/tex}

40{tex} \mathrm { cm } {/tex}

D

5{tex} \mathrm { cm } {/tex}

##### Explanation

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Q 19. We have two equilateral prisms {tex} A {/tex} and {tex} B . {/tex} They are made of materials having refractive index 1.5 and 1.6. For minimum deviation, incident angle will be

Small for prism {tex} A {/tex}

B

Small for prism {tex} B {/tex}

C

Equal for both the prisms

D

Can't be predicted

##### Explanation

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Q 20. A thin plano-convex glass lens {tex} ( \mu = 1.5 ) {/tex} has its plane surface silvered, and {tex} R {/tex} is the radius of curvature of curved part, then which of the following ray diagram is true for an object placed at {tex} O ? {/tex}

B

C

D

##### Explanation

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Q 21. In a Young's double slit experiment the intensity at a point where the path difference is {tex} \frac { \lambda } { 6 } ( \lambda {/tex} being the wavelength of light used) is {tex} I {/tex}. If {tex} I _ { 0 } {/tex} denotes the maximum intensity, {tex} \frac { I } { I _ { 0 } } {/tex} is equal to

{tex} \frac { 3 } { 4 } {/tex}

B

{tex} \frac { 1 } { \sqrt { 2 } } {/tex}

C

{tex} \frac { \sqrt { 3 } } { 2 } {/tex}

D

{tex} \frac { 1 } { 2 } {/tex}

##### Explanation

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Q 22. To demonstrate the phenomenon of interference we require two sources which emit radiation of

A

nearly the same frequency

B

the same frequency

C

different wavelength

the same frequency and having a definite phase relationship.

##### Explanation

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Q 23. The maximum number of possible interference maxima for slit-separation equal to twice the wavelength in Young's double-slit experiment is

A

infinite

five

C

three

D

Zero

##### Explanation

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Q 24. The angle of incidence at which reflected light in totally polarized for reflection from air to glass (refractive index {tex} n ) , {/tex} is

A

{tex} \sin ^ { - 1 } ( n ) {/tex}

B

{tex} \sin ^ { - 1 } ( 1 / n ) {/tex}

C

{tex} \tan ^ { - 1 } ( 1 / n ) {/tex}

{tex} \tan ^ { - 1 } ( n ) {/tex}

##### Explanation

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Q 25. A Young's double slit experiment uses a monochromatic source. The shape of the interference fringes formed on a screen

straight line

B

parabola

C

hyperbola

D

circle