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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.
| 101. |
`angle i lt ` critical angle : Partial reflection `:: angle i gt ` critical angle : ………………….. |
| Answer» Total internal reflection : If the angle of incidence is greater than the critical angle, then all the light gets reflected back into the dense medium | |
| 102. |
Light travels with a velocity `1.5xx10^(8)m//s` in a medium. On entering `2^(nd)` medium its velocity becomes `0.75xx10^(8)m//s`. What is the refractive index of the `2^(nd)` medium with respect to the first medium. |
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Answer» Given : `v_(1)=1.5xx10^(8)m//s` `v_(2)=0.75 xx 10^(8) m//s` To find : `" "_(2)n_(1)=`? Formula : ` " "_(2)n_(1)=(v_(1))/(v_(2))` Solution : `" "_(2)n_(1)=(1.5xx10^(8))/(0.75 xx 10^(8))` `" "_(2)n_(1)=2` Refractive index of `2^(nd)` medium with respect to `1^(st)` is 2. |
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| 103. |
The refractive indexes of four substances P,Q,R and S are 1.77, 1.52, 1.65 and 1.36 respectively. When light travelling in air is incident on these substances at equal angles, the angle of refraction will be the maximum in:A. substance PB. substance QC. substance RD. substance S |
| Answer» Correct Answer - d) | |
| 104. |
An object 2 cm tall is placed on the axis of a convex lens of focal length 5 cm at a distance of 10 m from the optical center of the lens. Find the nature, position and size of the image formed. Which case of image formation three times. Find the distance of the lens from the filament and the focal length of the lens. |
| Answer» Real and inverted, `v=+5` cm, The image is formed 5 cm behind the convex lens, 0.01 cm | |
| 105. |
An object, a convex lens of focal length `20 cm` and a plane mirror are arranged as shown in the figure. How far behind the mirror is the second image formed? A. `30 cm`B. `20 cm`C. `40 cm`D. `50 cm` |
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Answer» Correct Answer - C For convex lens, `1/v-1/-12=1/(+20) rArr v=-30 cm` This image `I_1` is therfore, `(30+10) cm or 40 cm` towards left of plane mirror. Therefore, second image `I_2` (by the plane mirror) will be formed `40cm` behind the mirror. |
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| 106. |
a) Draw a diagram to show how a converging lens focusses parallel rays of light. b) How would you after alter the above diagram to show how a converging lens can produce a beam of parallel rays of light. |
| Answer» b) Placed a source of light (say, a lighted bulb) at the focus of the converging lens. | |
| 107. |
A convex lens of focal length 10 cm is placed at a distance of 12 cm from a wall. How far from the lens should an object be placed so as to form its real image on the wall? |
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Answer» Here, the real image is formed on the wall which is at a distance of 12 cm from the convex lens. This means that the distance of image from the convex lens or image distance will be 12 cm. Since a real image is fomred on the right side of the lens, so this image distance will be positive. Now, Image distance, `v=+- 12` cm (A real image) Object distance, u=? (To be calculated) Focal length, f=+10 cm (it is convex lens) Putting these values in the lens formula: `1/v-1/u=1/f` We get: `1/12-1/u=1/10` `1/12-1/10=1/u` `(5-6)/(60)=1/u` `-1/60=1/u` So, Object distance, u=-60 cm Thus, the obect should be place at a distance of 60 cm in front of the convex lens. The minus sign shows that the obect is on the left side of the lens. |
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| 108. |
Fill in the following blanks with suitable words: a) The reciprocal of the focal length in metres gives you the ……………. Of the lens, which is measured in……………….. For converging lenses, the power is ……………… while for diverging lenses, the power is ............................. |
| Answer» a) power, dioptres b) positive, negative | |
| 109. |
A burning candle whose flame is 1.5 cm tall is placed at a certain distance in front of a convex lens. An image of candle flame is received on a white screen kept behind the lens. The image of flame also measures 1.5 cm. If f is the focal length of convex lens, the candle is placed.A. at fB. between f and 2fC. at 2fD. beyond 2f |
| Answer» Correct Answer - c) | |
| 110. |
A lens of focal length `12 cm` forms an upright image three times the size of a real object. Find the distance in cm between the object and image.A. 8 cmB. 16 cmC. 24 cmD. 36 cm |
| Answer» Correct Answer - b) | |
| 111. |
The distance between an object and its upright image is `20 cm.` if the magnification is `0.5,` what is the focal length of the lens that is being used to form the image? |
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Answer» Correct Answer - C::D Diminished erect image is formed by concave lens. Let `u=-x,` then `v=-x/2` Now, `|u|-|v|=20 cm` `:. x/2=20 cm or x=40 cm` `:. u=-40 cm and v=-20 cm` `1/f=1/-20-1/-40` or `f=-40 cm` |
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| 112. |
a) Explain why, a real image can be projected on a screen but a virtual image cannot. b) Draw a ray diagram to show the formation of a real diminished image of an object by a convex lens. In your diagram, the position of object and image with respect to the principle focus should be shown clearly. c) Name one simple optical instrument in which the above arrangement of convex lens is used. |
| Answer» c) A Simple camera | |
| 113. |
Which of the following diagrams shows correctly the dispersion of white light by a prism ? |
| Answer» Correct Answer - E | |
| 114. |
The power in dioptre of an equi-convex lens with radii of curvature of 10cm and refractive index 1.6 isA. `+1.2`B. `+18`C. `+1.2`D. `+1.8` |
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Answer» Correct Answer - A `1/f=P=(mu-1)(1/R_1-1/R_2)` `=(1.6-1)(1/0.1-1/(-0.1))` `=+12 D` |
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| 115. |
A thin equi-convex lens is made of glass of refractive index `1.5` and its length is `0.2 m.` If it acts as a concave lens of `0.5 m` focal length when dipped in a liquid, the refractive index of the liquid isA. `17/8`B. `15/8`C. `13/8`D. `9/8` |
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Answer» Correct Answer - B `1/0.2=(1.5-1)(1/R_1-1/R_2)…….(i)` `1/-0.5=(1.5/mu-1)(1/R_1-1/R_2)…..(ii)` Here, `mu=`refractive index of medium or liquid. Dividing Eq.(i) by Eq.(ii), we get `-5=1/((1.5//mu)-1) or mu=15/8` |
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| 116. |
The given equi-convex lens is broken into four parts and rearranged as shwon. If the initial focal length is f, then after rearrangement the equivalent focal length is A. `f`B. `f//2`C. `f//4`D. `4f` |
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Answer» Correct Answer - B Focal length of any one part will be `2f.` `:. 1/F=1/(2f)+1/(2f)+1/(2f)+1/(2f) or F=f/2` |
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| 117. |
Refractive indices of water, sulphric acid, glass and carbon disulphide are `1.33, 1.43, 1.53` and `1.63` respectively. The light travels slowest in:A. sulphiric acidB. glassC. waterD. carbon disulphide |
| Answer» Correct Answer - d) | |
| 118. |
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image? |
| Answer» Between F and 2F (or Between f and 2f) | |
| 119. |
A convex lens produces an inverted image magnified three times of an object placed of 15 cm from it. Calculate focal length of the lens. |
| Answer» Correct Answer - 11.2 cm | |
| 120. |
A convex lens of focal length 0.10 cm is used to form a magnified image of an object of height 5 mm placed a distance of 0.08 m form the lens. Calculate the position, nature and size of the image. |
| Answer» `v=-0.40`m, The position of image is 0.40 cm from the lens on the same side as the object (on the left of lens), The nature of image is virtual and erect, The size of image is 25 mm | |
| 121. |
a) What type of images can a convex lens make? b) What type of image is always made by a concave lens? |
| Answer» a) Real and Virtual, b) Virtual | |
| 122. |
An object of height 4.25 mm is placed at a distance 10 cm from a convex lens of power `+5`D. Find (i) focal length of the lens, and ii) size of the image. |
| Answer» i) 20 cm ii) 8.50 mm | |
| 123. |
A lens of focal length 20 cm is used to produce a ten times magnified image of a film slide on a screen. How far must the slide be placed from the lens? |
| Answer» 220 cm behind the lens | |
| 124. |
How would a pencil look like if you saw it through a) a concave lens, and b) a convex lens? (Assume the pencil is close to the lens). Is the image real or virtual? |
| Answer» a) Smaller b) Bigger, Virtual | |
| 125. |
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30cm, 40cm, 60cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24cm, 60cm, 30cm and 40 cm, respectively. Unfortunately his results are written in wrong order. a) Rewrite the image distancees in the correct order. b) What would be the image distance if the object distance was 90 cm? c) Which of the object distances gives the biggest image? d) What is the focal length of this lens? |
| Answer» a) 100 cm, 60 cm, 40 cm , 40cm, 24 cm b) 25.7 cm c) 25 cm d) 20 cm | |
| 126. |
A convex lens of power 5 D and a concave lens of power `7.5` D are placed in contact with each other. What is the: a) power of this combination of lenses? b) focal length of this combination of lenses? |
| Answer» a) `-2.5 D` b) `-40 cm` | |
| 127. |
A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with one another. a) What is the power of this combination? b) What is the focal length of this combination? c) Is the combinatioin converging or diverging? |
| Answer» a) `-6 D` b) `-16.66 cm` c) Diverging | |
| 128. |
A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:A. `+10 cm`B. `+20 cm`C. `-10 cm`D. `-20 cm` |
| Answer» Correct Answer - b | |
| 129. |
A convex lens of power `2 D` and a concave lens of focal length `40cm`are kept in contact, find (a) Power of combination , (b) Equivalent focal length |
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Answer» Correct Answer - B::C (a) Applying `P=P_1+P_2=P_("convex")+P_("concave")` `=2+(1)/((-0.4)) , [P("in" D)=(1)/(f(in m))]` `=2-2.5=-0.5D` (b) `F=1/P` `=1/(-0.5)=-2m` `=-200cm` |
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| 130. |
An achromatic lens-doublet is formed by placing in contact a convex lens of focal length `20 cm` and a concave lens of focal length `30 cm.` The dispersive power of the material of the convex lens is `0.8.` Determine the dispersive power of the material of the concave lens. Calculate the focal length of the lens-doublet. |
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Answer» Correct Answer - A::B::C (a) `(omega_1)/(f_1)+(omega_2)/(f_2)=0` `:. omega_2=(-f_2/f_1)omega_1` `=-((-30))/((+20))(0.18)=0.27` (b) `1/F=1/(f_1)+1/(f_2)=1/20-1/30` or `F=+60 cm` |
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| 131. |
A person got his eyes tested by an option. The prescription for the spectacle lenses to be made reads: Left eye: `+2.50`D Right eye: `+2.00` D a) State whether these lenses are thicker in the middle or at the edges. b) Which lens bends the light rays more strongly? c) State whether these spectacle lenses will converge light rays or diverge light rays. |
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Answer» a) Thicker In the middle b) Lens having greater power of `+2.50 D` c) Converging light rays. |
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| 132. |
The refracting angle of a prism is A and refractive index of the material of prism is `cot(A//2)` . The angle of minimum deviation will beA. `180^@-3A`B. `180^@+2A`C. `90^@-A`D. `180^@-2A` |
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Answer» Correct Answer - B `mu=(sin(A+delta_m)/2)/sin(A//2),` Given, `mu=cot(A/2)` Solving, we get `sin=180^@-2A` |
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| 133. |
Two thin similar convex glass are joined together front to front, with its rear portion silvered such that a sharp image is formed `0.2m` for an object at infinity. When the air between the glass pieces is replaced by water `(mu=4/3),` find the position of image. |
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Answer» Correct Answer - A::B::C It is just like a concave mirror. `|f|=0.2 m` `:. |R|=0.4 m` Focal length of this equivalent mirror is `1/F=(2(mu_2//mu_1))/R_2-(2(mu_2//mu_1-1))/R_1 ("extra points")` `=(2(4//3))/-0.4-(2(4//3-1))/(+0.4)` or `F=-0.12 m or -12 cm` |
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| 134. |
A lens with a focal length of `16 cm` produces a sharp image of an object in two positions, which are `60 cm` apart. Find the distance from the object to the screen. |
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Answer» Correct Answer - A::C `f=(d^2-x^2)/(4d)` (displacement method) `f=16 cm,x=60 cm` Substituting the values we get, `d=100cm` |
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| 135. |
Two convex lenses of focal length `10 cm` and `20 cm` respectively placed coaxially and are separated by some distance d. The whole system behaves like a concave lens. One of the possible value of d isA. `15 cm`B. `20 cm`C. `25 cm`D. `40 cm` |
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Answer» Correct Answer - B `1/F=1/(f_1)+1/(f_2)-d/(f_1f_2)` To behave like concave lens, F should be negative. So, `d/(f_1f_2)gt1/(f_1)+1/(f_2)` or `d/(f_1f_2)gt(f_1+f_2)/(f_1f_2)` or `dgt(f_1+f_2) or 30 cm` |
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| 136. |
Two glasses with refractive indices of `1.5 and 1.7` are used to make two indentical double convex lenses. Find the ratio between their focal lengths. How will each of these lenses act on a ray parallel to its optical axis if the lenses are submerged into a transparent liquid with a refractive index of `1.6?` |
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Answer» Correct Answer - A::B::C::D (a) `1/f=(mu-1)(1/R_1-1/R_2)` `:. fprop(1/(mu-1))` or `f_1/(f_(2))=(mu_2-1)/(mu_1-1)=(1.7-1.0)/(1.5-1.0)=1.4` (b) If refraction index of the liquid (or the medium) is greater than the refraction index of lens it changes its nature of converging lens behaves as diverging. |
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| 137. |
You must have seen chandeliers having glass prism. The light from a tungsten bulb gets dispersed white passing through these prisms and we see coloured spectrum. If we use on LED light instead of tungsten bulb, will we be able to see the same effect ? |
| Answer» Yes, We can see the same effect for LED light also. But the spectrum obtained is not continuous as in the case of sunlight. | |
| 138. |
(i) Keep a glass slab on a blank paper and draw its outline PQRS as shown in the figure. (ii) Draw an inclined straight line on the side of PQ so that it intersect PQ at N. Pierce two pins vertically at two points A and B along the line. (iii) Look at the pins A and B from the opposite side of the slab and pierce pins C and D vertically so that the images of A and B are in line with C and D. (iv) Now remove the chip and the pins and draw a straight line going through points C and D so that it intersects SR at M. (v) Join points M and N. Observe the incident ray AN and emergent ray MD. Questions: (a) What is your observation about the emergent ray and incident ray ? |
| Answer» Incident ray and emergent ray lie parallel to each other. | |
| 139. |
State any one phenomenon in nature which is based on total internal reflection. |
| Answer» Mirage or Rainbow formation. | |
| 140. |
Find the Odd one out:Reflection, dispersion, refractive index, refraction |
| Answer» Refractive index. Refractive index is a value while the rest are natural phenomena of light. | |
| 141. |
A plane glass slab is placed over various coloured letters. The letter which appears to be raised the least isA. violetB. yellowC. redD. green |
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Answer» Correct Answer - C `d_("app.")=d/mu` `mu` or red is least. So, `d_("app.")` For red is maximum. So, they appear to be raised least. |
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| 142. |
A star appears twinkling in the sky because of _______ by the atmosphere . |
| Answer» Atmospheric refraction | |
| 143. |
Spectrum : Dispersion : : Twinkling of stars : …………… |
| Answer» Refraction : Spectrum is formed by dispersion of white light or sunlight, whereas the changes in the refractive index of air stars appear to twinkle. | |
| 144. |
Stars twinkle at night. |
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Answer» (i) Stars are self luminous and can be seen at night in the absence of sunlight. (ii) They appear to be point sources as they are at a very large distance from us. (iii) The apparent position of the star keeps changing a bit because of the motion of atmospheric air and changing air density and temperature. (iv) Because of this, refractive index of air keeps changing continuously. (v) So the position and brightness of the stars keeps changing and so the stars appear to be twinkling. |
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| 145. |
Which causes more bending (or more refraction) of light rays passing through it, a convex lens of long focal length or a convex lens of short focal length? |
| Answer» Convex lens of short length. | |
| 146. |
A bird is flying over a swimming pool at a height of `2m` from the water surface. If the bottom is perfectly plane reflecting surface and depth of swimming pool is `1m,` then the distance of final image of bird from the bird itself is `mu_w=4//3`A. `11/3 m`B. `23/3 m`C. `11/4 m`D. `11/2 m` |
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Answer» Correct Answer - D `h_(app)=muh=4/3xx2=8/3m` `Distance from mirror=1+h_(app)=11/3m.` So, mirror will make image at same distance (`=11//3m` from itself). Now in third refraciton, depth of second image, `d=11/3+1=14/3 m` `d_(app)=d/mu=14/3xx3/4=7/2m` The desired distance is therefore, `(d_(app)+h)` or `(7/2+2)m or 11/2m` |
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| 147. |
The index of refraction of heavy flint glass is `1.68` at `434 nm` and `1.65` at `671nm`. Calculate the difference in the angle of deviation of blue `(434 nm)` and red `(671 nm)` light incident at `65^@` on one side of a heavy flint glass prism with apex angle `60^@`. |
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Answer» Correct Answer - B For blue light, `mu=(sin i_1)/(sinr_1)` or `1.68=(sin65^@)/(sinr_1)` Solving this equation, we get `r_1=32.6^@` `r_2=A-r_1=27.4^@` Again applying, `mu=(sini_2)/(sinr_2 )or 1.68=(sin i_2)/(sin27.4^@)` Solving this equation, we get `i_2=50.6^@` Now, `delta_B=i_1+i_2-A` or `delta_B=65^@+50.6^@-60^@=55.6^@.....(i)` For red light, `1.65=(sin65^@)/(sinr_1)` or `r_1=33.3^@` `:. r_2=A-r_1=26.7^@` Now, `1.65=(sini_2)/(sin26.7^@)` `:. i_2=47.8^@` `:. delta_R=i_1+i_2-A` or `delta_R=65^@+47.8^@-60^@=52.8^@`....(ii)` From Eqs (i) and (ii), we get `delta_B-delta_R=2.8^@` |
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| 148. |
Only one of the following applies to a concave lens. This is:A. a focal length is positiveB. image distance can be positive or negativeC. height of image can be positive or negativeD. image distance is always negative. |
| Answer» Correct Answer - d) | |
| 149. |
The magnification produced by a spherical mirror and a spherical lens is `+0.8`.A. The mirror and lens are both convexB. The mirror and lens are both concaveC. The mirror is concave but the lens is convex.D. The mirror is convex but the lens is concave. |
| Answer» Correct Answer - d) | |
| 150. |
The magnification produced by a spherical lens and a spherical mirror is `+2.0`.A. The lens and mirror are both concaveB. The lens and mirror are both convexC. The lens is convex but the mirror is concaveD. The lens is concave but the mirror is convex. |
| Answer» Correct Answer - c) | |