

InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
601. |
A convex lens is used to throw on a screen `10 m` from the lens, a magnified image of an object. If the magnification is to be `19`, find the focal length of the lens. |
Answer» Correct Answer - `0.5 m` Here, `v = 10 m, m = - 19, f = ?` `m = (f - v)/(f)` `-19 = (f - 10)/(f)` or `-19 f = f - 10` or `20 f = 10` `f = 0.5 m` |
|
602. |
The focal lengths of objective and eye piece of a microscope are `1.25 cm and 5 cm` respectively. Find the position of the object relative to the objective in order to obtain an angular magnification of `30` in normal adjustment. |
Answer» Here, `f_(0) = 1.25 cm, f_(e) = 5 cm, mu_(0) = ?`, `m = 30` In normal adjustment, magnification produced by the eye piece, `m_(e) = (d)/(f_(e)) = (25)/(5) = 5` As `m = m_(0) xx m_(e) :. m_(0) = (m)/(m_(e)) = (30)/(5) = 6` As real image is formed by objective lens, therefore, `m_(0) = (v_(0))/(u_(0)) = -6, v_(0) = -6 u_(0)` From `(1)/(v_(0)) - (1)/(u_(0)) = (1)/(f_(0))` `(1)/(-6 u_(0)) - (1)/(u_(0)) = (1)/(1.25) or = u_(0) = (- 7 xx 1.25)/(6)` `= - 1.46 cm` `:.` Object must be held `1.46 cm` in front of objective lens. |
|
603. |
An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is,(a) 8 cm (b) 10 cm (c) 12 cm (d) 16 cm |
Answer» (c) 12 cm Let d1 = 5 cm and d2 = 3 cm ; n = 1.5 Actual width is the sum of real depth from 2 sides Thickness of slab = d1n + d2n = (5 x 1.5) +(3 x 1.5)= 12 cm |
|
604. |
A transparent thin film of uniform thickness and refractive index `n_(1)``=1.4` is coated on the convex spherical surface of radius R at one end of a long solid glass cylinder of refractive index `n_(2)``=1.5`, as shown in the figure. Rays of light parallel to the axis of the cylinder traversing through the film from air to glass get focused at distance `f_(1)` from the film, while rays of light traversing from glass to air get focused at distance `f_(2)` from the film, Then ` A. `|f_(1)| = 3 R`B. `|f_(1)| = 2.8 R`C. `|f_(2)| = 2 R`D. `|f_(2)| = 1.4 R` |
Answer» Correct Answer - A::C As thickness of film is uniform, the effective power of the film is zero. Therefore, we can consider refraction at glass air interface. In case I : Refraction from air to glass `-(mu_(1))/(u) + (mu_(2))/(v) = (mu_(2) - mu_(1))/(R )` `-(1)/(oo) + (1.5)/(f_(1)) = (1.5 - 1)/(R )` or `f_(1) = 3 R` In case II : Refraction from denser to rarer `-(mu_(2))/(u) + (mu_(1))/(v) = (mu_(1) - mu_(2))/(R )` `-(1.5)/(oo) + (1)/(f_(2)) = (1 - 1.5)/(R )` or `f_(2) = 2 R` Choice (a) and ( c) are correct. |
|
605. |
A thin equiconvex lens has focal length 10 cm and refractive index 1.5 . One of its faces is now silvered and for an object placed at a distance u in front of it, the image coincides with the object. The value of u isA. 10 cmB. 5 cmC. 20 cmD. 15 cm |
Answer» Correct Answer - B |
|
606. |
A setting sun appears to be at an altitude higher than it really is. This is because of (a) absorption of light (b) reflection of light (c) refraction of light (d) dispersion of light |
Answer» (c) refraction of light This is due to refraction of light by the earth’s atmosphere. |
|
607. |
In an astronomical telescope in normal adjustment a straight black line of length `L` is drawn on inside part of objective lens. The eye piece forms a real image of this line. The length of this image is `I`. The magnification of the telescope isA. `L/l`B. `L/l+1`C. `L/l-1`D. `(L+1)/(L-l)` |
Answer» Correct Answer - A |
|
608. |
Line spectrum can be obtained from (a) sun (b) candle (c) mercury vapour lamp (d) electric bulb |
Answer» (c) mercury vapour lamp |
|
609. |
The…………..distance between two objects which………….is called……………….of the instrument. |
Answer» minimum , can just be seen as separate , limit of resolution. | |
610. |
When an unpolarised light is polarized, then the intensity of light of the polarized waves |
Answer» a polarizing sheet , half the original intensity. | |
611. |
When angles between principal sections of two nicols are `0^(@)` and `180^(@)`, they are referred to as……….. . |
Answer» Correct Answer - parallel nicols | |
612. |
What are mirage and looming? |
Answer» Mirage: Mirage takes place in hot regions. The light from distant objects appears to be reflected from ground. For mirage to form refractive index goes on increasing as we go up. Looming: Looming takes place in cold regions. The light from distant objects appears to be flying. For looming to form refractive index goes on decreasing. |
|
613. |
Write a note on optical fibre. |
Answer» Transmitting signals through optical fibres is possible due to the phenomenon of total internal reflection. Optical fibres consists of inner part called core and outer part called cladding (or) sleeving. The refractive index of the material of the core must be higher than that of the cladding for total internal reflection to happen. Signal in the form of light is made to incident inside the core-cladding boundary at an angle greater than the critical angle. Hence, it undergoes repeated total internal reflections along the length of the fibre without undergoing any refraction. |
|
614. |
Write a short notes on the prisms making use of total internal reflection. |
Answer» Prisms can be designed to reflect light by 90° or by 180° by making use of total internal reflection. The critical angle ic for the material of the prism must be less than 45°. This is true for both crown glass and flint glass. Prisms are also used to invert images without changing their size. |
|
615. |
Assertion: The refractive index of a prism depends only on the material of the prism. Reason: The refractive index of a prism depends upon the refracting angle and angel of minimum deviation. (a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion. (c) If Assertion is true but Reason is false. (d) If Assertion is false but Reason is true. |
Answer» (c) If Assertion is true but Reason is false. |
|
616. |
Assertion: If a convex lens is placed in water, its convergence power decrease. Reason: Focal length of lens is independent of refractive index of the medium. (a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion. (c) If Assertion is true but Reason is false. (d) If Assertion is false but Reason is true. |
Answer» (c) If Assertion is true but Reason is false. |
|
617. |
What is refractive index? |
Answer» Refractive index gives us an idea of how fast or how slow light travels in a medium. |
|
618. |
What is Snell’s window? |
Answer» When light entering the water from outside is seen from inside the water, the view is restricted to a particular angle equal to the critical angle ic. The restricted illuminated circular area is called Snell’s window. |
|
619. |
State Snell’s law. |
Answer» The ratio of the sine of the angle of incidence and sine of the angle of refraction is equal to the ratio of refractive indices of the two media. This law is also known as Snell’s law. \(\frac{sin i}{sin r} = \frac{μ_2}{μ_1}\) |
|
620. |
The law of distances is given by: |
Answer» Correct answer is (b) \(\frac{1}{f} = \frac{1}{u} + \frac {1}{v}\) |
|
621. |
True or False. If false correct it. 1. light does not travel along a straight line. 2. All coloured light has same wavelenth.3. In refraction incident ray, refracted ray and normal lie in the same plane. 4. Velocity of light is greater in rarer medium is greater than that in denser medium. 5. For red colour angle of refraction is the least. 6. The refractive index of a medium is independent of wavelength. 7. Tyndall scattering, is the scattering of light by colloids. 8. According to Rayleigh’s scattering law, red colour is scattered to a greater extent than blue colour. 9. Mie scattering takes place when the diameter is larger than the wavelength of the incident light. 10. The lines in Raman scattering having frequencies lower than the incident frequency are called Antistoke’s lines. 11. In front of a convex lens when the object is placed at infinity the formed image is smaller than that of the object. 12. When an object is placed at finite distance from the concave lens a virtual image is formed between optical centre and focus of the concave lens. 13. Pupil of human eye bends the incident light on to the lens. 14. For a normal human eye, the value of far point is 25 cm. 15. Astigmatism is corrected by cylindrical lenses. |
Answer» 1. False – Light always travels along a straight lines. 2. False – Different coloured light has different wavelength. 3. True 4. True 5. True 6. False – The refractive index of a medium depends on wavelength. 7. True 8. False – According to Rayleigh’s scattering law, blue colour is scattered to a greater extent than red colour. 9. True 10. False – The lines in Raman scattering having frequencies higher than the incident frequency are called Antistoke’s lines. 11. True 12. True 13. False – Cornea of human eye bends the incident light on to the lens. 14. False – For a normal human eye, the value of near point is 25 cm. 15. True |
|
622. |
The unit of focal length is: (a) dioptre (b) metre (c) ohm (d) ampere |
Answer» Correct answer is (b) metre |
|
623. |
Fill in the blanks1. The velocity of light in vacuum is ………. 2. If v is the frequency and λ is the wavelength then velocity of the wave is c = ………. 3. Among colours of visible light ……… colour has the highest wavelength. 4. According to Snell’s law refractive index, µ2 = ……….5. In a medium having high value of refractive index then speed of light in that medium is ………. 6. Angle of refraction is the smallest for ……… and the highest for ………. 7. The refractive index depends on ………. of light. 8. Colours having shorter wavelength scattered more than longer wavelength colours according to ……….. law. 9. After passing through a convex lens ……….. rays ………. at the principal focus. 10. For a convex lens, as the object distance increases, the image distance ………. 11. A ray passing through the optic centre of a lens emerges …………12. ……… is due to irregular curvature of the surface of the eye lens. 13. When a parallel beam of light passes through a convex lens, the rays from the outer edges are ………… 14. A ray parallel to the principal axis of a convex lens after refraction passes through ………… 15. When the object is placed between ………….. and ………… of a convex lens a virtual image will be formed. 16. For a convex lens, as the object approaches the lens the image becomes …………17. In a phographic camera ………… lens is used. 18. The shorter the focal length, the ………. is the magnification. 19. The nature of the image formed by a simple microscope is ……….., ………… and ………… 20. Real images are formed by a ……….. lens. 21. Concave lens produces ………… images. 22. The value of power of a lens having focal length one metre is ……….. 23. For a normal eye the value of far point is ………… 24. …………. is known as short sightedness. 25. Hyper metropia is known as ……….. 26. The mathematical form of focal length of a concave lens used to correct myopia is f = ………. 27. ……….. lenses are used to correct astigmatism. 28. For a normal eye, the value of least distance of distinct vision is ……….. 29. The objective of the compound microscope has …………. focal length. 30. The focal length of ………. is greater in a compound microscope. 31. ……… is an optical instrument to see the distant objects. 32. A terrestrial telescope produces ……… image.33. Elaborate view of galaxies and planets is obtained by ……… |
Answer» 1. 3 × 108 m/s 2. vλ 3. red 4. \(\frac{sin\,i}{sin\,r}\) 5. low 6. red, violet 7. wavelength 8. Rayleigh scattering 9. parallel, converge 10. will decrease 11. undeviated 12. Astigmatism 13. deviated towards the centre of the lens 14. the principal focus 15. principal focus, optical centre 16. bigger 17. biconvex 18. greater 19. virtual, erect, magnified 20. convex 21. virtual 22. One dioptre 23. infinity 24. Myopia 25. long sightedness 26. xy/x – y 27. Cylindrical 28. 25 cm 29. shorter 30. eye piece 31. Telescope 32. an erect 33. Telescope |
|
624. |
The unit of power is: (a) m (b) ohm (c) dioptre (d) ampere |
Answer» Correct answer is (c) dioptre |
|
625. |
The magnification in terms of object distance u and image distance v is m :(a) \(\frac {u}{v}\)(b) u + v(c) \(\frac{v}{u}\)(d) uv |
Answer» Correct answer is (c) \(\frac {v}{u}\) |
|
626. |
The sign of focal length of a convex lens is ………. sign. (a) negative (b) positive (c) negative or positive (d) none of the above |
Answer» Correct answer is (b) positive |
|
627. |
If the focal length of a convex lens is 1 m then its power is :(a) 1 dioptre(b) 0.1 dioptre(c) 10 dioptre(d) 0.01 dioptre |
Answer» (a) 1 dioptre |
|
628. |
In terms of object distance u and focal length/, magnification is given by m =(a) u - f(b) \(\frac{f}{u-f}\)(c) \(\frac{u - f}{f}\)(d) \(\frac{u+f}{f}\) |
Answer» Correct answer is (b) \(\frac{f}{u - f}\) |
|
629. |
Magnification of a convex lens is _____. (a) positive (b) negative (c) either positive or negative (d) zero. |
Answer» Correct answer is (b) negative |
|
630. |
Match the column I with Column II.Column IColumn IIA.Refractive index(i)\(\frac{image \,distance} {object \,distance}\)B.Power of a lens(ii)convex lensC.Hypermetropia(iii)DioptreD.Magnification(iv)\(\frac{speed\, of\,light\,in\,air}{speed \,of\,light\,in\,medium}\) |
Answer» A. (iv) B. (iii) C. (iv) D. (i) |
|
631. |
The magnifying power of compound microscope is : (a) 10 (b) 20 (c) 50 (d) 50 to 200 |
Answer» Correct answer is (d) 50 to 200 |
|
632. |
In a simple microscope, the magnification can be increased by : (a) lens of long focal length (b) lens (c) lens of short focal length(d) lens of infinite focal length |
Answer» (c) lens of short focal length |
|
633. |
The accuracy of travelling microscope is of the order of : (a) 0.01 cm (b) 0.01 mm (c) 0.1 mm (d) 0.1 cm |
Answer» Correct answer is (b) 0.01 mm |
|
634. |
What are the uses of simple microscope ? |
Answer» Simple microscopes are used 1. By watch repairers and jewellers. 2. To read small letters clearly. 3. To observe parts of flowers, insects etc. 4. To observe finger prints in the field of forensic science. |
|
635. |
What is a lens ? |
Answer» A lens is an optically transparent medium bounded by two spherical refracting surfaces or one plane and one spherical surface. |
|
636. |
State the principle of microscope. How is it classified ? |
Answer» It works under the principle of angular magnification of lenses. It is classified as 1. Simple microscope 2. Compound micriscope |
|
637. |
A biconvex lens is made of glass with `mu = 1.52`. Each surface has a radius of curvature equal to `30 cm`. An object of height `3 cm` is placed `14 cm` from the lens. Find the focal length of the lens and the position and size of image. |
Answer» Correct Answer - `28.85 cm. -27.19 cm. 5.82 cm` ; enlarged, erect and virtual | |
638. |
How is lens classified ? |
Answer» Lens is basically classified into two types. They are : 1. Convex lens 2. Concave lens. |
|
639. |
What is biconvex lens ? |
Answer» Convex or bi-convex lens: It is a lens bounded by two spherical surfaces such that it is thicker at the centre than at the edges. A beam of light passing through it, is converged to a point. So, a convex lens is also called as converging lens. |
|
640. |
What are the disadvantage of telescope? |
Answer» 1. Frequent maintenance is needed. 2. It is not easily protable. |
|
641. |
Define power of a lens. State its unit. |
Answer» Power of a lens is numerically defined as the reciprocal of its focal length. P = \(\frac{1}{f}\) The SI unit of power of a lens is dioptre. |
|
642. |
State the Laws of Refraction. |
Answer» The incident ray, the refracted ray of light and the normal to the refracting surface all lie in the same plane. Second law of Refraction: 1. The ratio of the sine of the angle of incidence and sine of the angle of refraction is equal to the ratio of refractive indices of the two media. This law is also known as Snell’s law. \(\frac{sin\, i}{sin\, r} = \frac{μ_2}{μ_1}\) 2. Refractive index gives us an idea of how fast or how slow light travels in a medium. The ratio of the speed of light in a vacuum to the speed of light in a medium is defined as the refractive index ‘µ’ of that medium. 3. The speed of light in a medium is low if the refractive index of the medium is high and vice versa. 4. When light travels from a denser medium into a rarer medium, the refracted ray is bent away from the normal drawn to the interface. 5. When light travels from a rarer medium into a denser medium, the refracted ray is bent towards the normal drawn to the interface. |
|
643. |
What is meant by biconcave lens? |
Answer» Concave or bi-concave Lens: It is a lens bounded by two spherical surfaces such that it is thinner at the centre than at the edges. A parallel beam of light passing through it, is diverged or spread out. So, a concave lens is also called as diverging lens. |
|
644. |
What is meant by power of lens? |
Answer» The ability of a lens to converge (convex lens) or diverge (concave lens) light rays is called as its power. |
|
645. |
State laws of refraction. |
Answer» First law of refraction: The incident ray, the refracted ray of light and the normal to the refracting surface all lie in the same plane. Second law of refraction: The ratio of the sine of the angle of incidence and sine of the angle of refraction is equal to the ratio of refractive indices of the two media. This law is also known as Snell’s law. \(\frac{sin \, i}{sin\, r} = \frac{μ_2}{μ_1}\) |
|
646. |
What is meant by monochromatic source? |
Answer» If a source of light produces a light of single colour, it is known as a monochromatic source |
|
647. |
Define refractive index of a medium. |
Answer» The ratio of speed of light in vacuum to the speed of light in a medium is defined as refractive index 'p' of that medium. |
|
648. |
An astronomical refractive telescope has an objective of focal length `20 m` and an eyepiece of focal length `2 cm`.A. The length of the telescope tube is `20.02 m`.B. The magnification is `1000`.C. The image formed is inverted.D. An objective of a larger aperture will increase the brightness and reduce chromatic aberration of the image. |
Answer» Correct Answer - A::B::C Here, `f_(0) = 20 m and f_(e) = 2 cm = 0.02 m`. In normal adjustment, length of telescope tube `L = f_(0) + f_(e) = 20.02 m` Magnification `= (f_(0))/(f_(e)) = (20)/(0.02) = 1000`. The image formed is inverted (w.r.t. the object). Choice (a), (b) and (c ) are correct. |
|
649. |
A swimmer `S` inside water is vertically above a fixed point `P`. A rectangular glass slab `B` is placed between `S` and `P`. As been by `S`, the position of `P` will appear to change, ifA. `B` is moved horizontallyB. `B` is moved verticallyC. `S` moves horizontallyD. `S` moves vertically |
Answer» Correct Answer - C |
|
650. |
A stationary swimmer `S`, inside a liquid of refractive index `mu_(1)`, is at a distance `d` from a fixed point `P` inside the liquid. A rectangular block of width `t` and refractive index `mu_(2)(mu_(2) lt mu_(1))` is now placed between `S` and `P.S` will observer `P` to be at a distanceA. `d-t((mu_(1))/(mu_(2))-1)`B. `d-t(1-(mu_(2))/(mu_(1)))`C. `d+t(1-(mu_(2))/(mu_(1)))`D. `d+t((mu_(1))/(mu_(2))-1)` |
Answer» Correct Answer - D |
|