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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.
| 951. |
Fraunhofer spectrum is aA. Line absorption spectrumB. Band absorption spectrumC. Line emission spectrumD. Band emission spectrum |
| Answer» Correct Answer - a | |
| 952. |
Continuous spectrum is not due toA. Hydrogen flameB. Electric bulbC. Kerosene oil lamp flameD. Candle flame |
| Answer» Correct Answer - a | |
| 953. |
Fraunhofer lines are produced byA. The element present in the photoshere of sunB. The elements present in the chromosphere of the sunC. The vapour of the element present in the chromosphere of the sunD. The carbon dioxide present in the atmosphere |
| Answer» Correct Answer - c | |
| 954. |
A convex lens, a glass slab, a glass prism and a solid sphere all are made of the same glass, the dispersive power will beA. In the glass slab and prismB. In the lens and solid sphereC. Only in prismD. In all the four |
| Answer» Correct Answer - d | |
| 955. |
A medium is said to be dispersive ifA. Light of different wavelength propagate at different speedsB. Light of different wavelengths propagate at same speed but has different frequenciesC. Light is gradually bent rather than sharply refracted at an interface between the medium and airD. Light is never totally internally reflected |
| Answer» Correct Answer - a | |
| 956. |
A ray of light is incident at an angle of `60^(@)` on one face of a prism of angle `30^(@)`. The ray emerging out of the prism makes an angle of `30^(@)` with the incident ray. The emergent ray isA. Normal to the face through which it emergesB. Inclined at `30^(@)` to the face through which it emergesC. Inclined at `60^(@)` to the face through which it emergesD. None of these |
| Answer» Correct Answer - a | |
| 957. |
The focal length of a plano-concave lens is -10 cm , then its focal length when its palne surface is polished isA. 20 cmB. `-5 cm `C. 5 cmD. `-20 cm ` |
| Answer» Correct Answer - C | |
| 958. |
Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod the light once entered into it will not leave it through its lateral face whatsoever be the value of angle of incidence.A. `n gt sqrt(2)`B. n=1C. n=1.1D. n=1.3 |
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Answer» Correct Answer - A |
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| 959. |
The ratio of the refractive index of red light to blue light in air isA. Less than unityB. Equal to unityC. Greater than unityD. Less as well as greater than unity depending upon the experimental arrangemen |
| Answer» Correct Answer - a | |
| 960. |
Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod the light once entered into it will not leave it through its lateral face whatsoever be the value of angle of incidence.A. `n gt sqrt2`B. `n = 1`C. `n = 1.1`D. `n = 1.3` |
| Answer» Correct Answer - A | |
| 961. |
The refractive index of a piece of transparent quartz is the greatest forA. Red lightB. Violet lightC. Green lightD. Yellow light |
| Answer» Correct Answer - b | |
| 962. |
A wiere mesth consisting of very small squares is viewed at a distances of `8cm` through a magnifying lens of fcoal length `10cm`, kept close to the eye. The magnification produced by the lens isA. 5B. 8C. 10D. 20 |
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Answer» (a) `1/f=1/v-1/u`………(i) Given `f=10cm` (as lens is converging) `u=-8cm` (as object is placed on left side on the lens) Substituting these values in Eq. (i) We get `1/10=1/v-1/(-8)implies1/v=1/10-1/8implies1/v=(8-10)/80` `:. V=80/(-2)=-40cm` Hence, magnification produced by the lens `m=v/u=(-40)/(-8)=5` |
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| 963. |
A point object is kept at the first focus of convex lens ,if the lens starts moving towards right will a constant velocity,th image will A. always move towards rightB. always move towards leftC. first move towards right &then towards leftD. first move towards left &then towards right |
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Answer» Correct Answer - D `(dv)/(dt)=((v)/(u))^(2)xx(du)/(dt)` `V_("image/lens")=((v)/(u))^(2)xxV_("object/lens")` till `u` become `2f mgt-1"so" V_("image/lens")gtV_("object/lens")` and image will moves towards left and when `u "become" gt 2fV_("image/lens")ltV_("object/lens")`and image will moves towards right. |
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| 964. |
The focal length of convex tens is `f` and the distance of an object from the principal focus is x. The ratio of the size of the real image to the size of the object isA. `(f+x)/(f)`B. `f/x`C. `sqrt(f/x)`D. `f^(2)/x^(2)` |
| Answer» Correct Answer - b | |
| 965. |
The radii of curvature of the surfaces of a double convex lens are `20 cm and 30 cm`. What will be its focal length and power in air and water respectively ? Refractive indices for glass and water are `3//2 and 4//3` respectively. |
| Answer» Correct Answer - `24 cm, 4.17 D ; 96 cm, 1.04 D` | |
| 966. |
The radii of curvature of the surfaces of a double convex lens are `20 cm and 40 cm` respectively, and its focal length is `20 cm`. What is the refractive index of the material of the lens ? |
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Answer» Here, `R_1 = 20 cm, R_2 = -40 cm, f = 20 cm, mu = ?` As `(1)/(f) = (mu - 1)((1)/(R_1) - (1)/(R_2))` `:. (1)/(20)=(mu - 1)((1)/(20) + (1)/(40)) = (mu - 1) (3)/(40)` or `(mu - 1) = (2)/(3)` or `mu = (2)/(3)+ 1 = (5)/(3)`. |
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| 967. |
The radius of curvature of the curved surface of a plano-convex lens is `20 cm`. If the refractive index of the material of the lens be `1.5`, it willA. act as a convex lens only for the objects that lie on its curved sideB. act as a concave lens for the objects that lie on its curved sideC. act as a convex lens irrespective of the side on which the object liesD. act as a concave lens irrespective of side on which the object lies |
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Answer» Correct Answer - C (c ) Here, R=20 cm ,`mu`=1.5, on substituting the values in `f=R/(mu-1)=20/(1.5-1)=40`cm of converging nature as `fgt0`. Therefore, lens act as a convex lens irrespective of the side on which the object lies. |
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| 968. |
An object is placed 30cm away from a convex lens of focal length 10cm and a sharp image is formed on a screen. Now, a convex lens is placed In contact with the convex lens. The screen now has to be moved by 45cm to get a sharp image again. The magnitude of focal length of the convex lends in (in cm)A. 72B. 60C. 36D. 20 |
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Answer» Correct Answer - D For the best first condition, `f_(1)=10cm u=-30cm` then, `(1)/(f_(1))=(1)/(v)-(1)(u) Rightarrow=(1)/(v)+(1)/(30)` `(1)/(v)=(1)/(10)-(1)/(30) Rightarrow v=(30)/(2)=15` For the second condition, when concave lens is placed, (where F=focal length of combination) `therefore(1)/(F)=(1)/(60)+(1)/(30)=F=(60)/(3)=20cm` The magnitude of focal length of concave lens, `(1)/(F)=(1)/(f_(1))+(1)/(f_(2)) Rightarrow (1)/(20)=(1)/(10)+(1)/(f_(2))` `f_(2)`=-20(negative sign for concave lens) |
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| 969. |
A concave lens has same radii of curvature for both sides and is made of material of refractive in index `1.6` It is immersed in a liquid of `mu = 1.4` Calculate ratio of focal lengths of lens in air and liquid. |
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Answer» Correct Answer - `0.238` Use `(1)/(f_a) = ((mu_g)/(mu_a) - 1) ((1)/(R_1) - (1)/(R_2))` and `(1)/(f_1) = ((mu_g)/(mu_l) - 1) ((1)/(R_1) - (1)/(R_2))`. |
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| 970. |
Find the change in the focal lengthof the lens, if a convex lens of focal length `20cm` and refractive index `1.5`, is immersed in water having refractive index `1.33`.A. `62.2cm`B. `5.82cm`C. `58.2cm`D. `6.22cm` |
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Answer» (c) When the lens is in air `1/(f_(a))=(mu-1)(1/(R_(1))-1/(R_(2)))` `1/20=(1.5-1)(1/(R_(1))-1/(R_(2)))` or `(1/(R_(1))-1/(R_(2)))=1/10` When lens is in water `1/(f_(w))=((mu_(g)-mu_(w))/(mu_(w)))(1/(R_(1))-1/(R_(2)))=((1.5-1.33)/1.33)xx1/10` `f_(w)=78.2cm` The change in focal length`=78.2-20=58.2cm` |
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| 971. |
Two identical glass rods `S_(1)` and `S_(2)` (refractive index=1.5) have one convex end of radius of curvature 10 cm. They are placed with the curved surfaces at a distance d as shown in the figure, with their axes (shown by the dashed line) aligned. When a point source of light P is placed inside rod `S_(1)` on its axis at a distance of 50 cm from the curved face, the light rays emenating from it are found to be parallel to the axis inside `S_(2)`. The distance d is A. 60 cmB. 70 cmC. 80 cmD. 90 cm |
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Answer» Correct Answer - B For `S_1` (Refraction from denser to rarer medium) `u = -50 cm, R = -10 cm` `(mu_2)/(-u)+(mu_1)/(v)=(mu_1 - mu_2)/( R)` `(3//2)/(-(-50))+(1)/(v)=(1 -3//2)/(-10)` or `(1)/(v)+(3)/(100)=(1)/(20)` `(1)/(v)=(1)/(20)-(3)/(100)=(1)/(50)` `v = 50 cm` for `S_2` Refraction from rarer to denser medium `:. u rarr -(d = 50), v = oo, R_2 = R` `(mu_1)/(-u)+(mu_2)/(v)=(mu_2 - mu_1)/( R)` `(1)/((d - 50))+ (3//2)/(oo) = (1)/(20)` `d = 70 cm`. |
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| 972. |
The radius of curvature of the curved surface of a plano-convex lens is `20 cm`. If the refractive index of the material of the lens be `1.5`, it willA. `30 cm`B. `50 cm`C. `20 cm`D. `40 cm` |
| Answer» Correct Answer - d | |
| 973. |
A plano convex lens of refractive index 1.5 and radius of curvature 30cm. Is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object.A. `20 cm`B. `30 cm`C. `60 cm`D. `80 cm` |
| Answer» Correct Answer - a | |
| 974. |
At what distance from a convex lens of focal length `30cm` an object should be placed so that the size of image be `(1)/(4) `that of object?A. `30 cm`B. `60 cm`C. `15 cm`D. `90 cm` |
| Answer» Correct Answer - d | |
| 975. |
A diverging lens of refractive index `1.5` and focal length `15 cm` in air has same radii of curvature for both sides. If it is immersed in a liquid of refractive index `1.7`, calculate focal length of the lens in liquid. |
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Answer» Correct Answer - `-63.75 cm` Here, `mu_g = 1.5, f_a = 15 cm, f_l = ?, mu_l = 1.7` If `R_1 = R, R_2 = -R` From `(1)/(f) = (mu - 1) ((1)/(R_1) - (1)/(R_2))` =`(mu - 1)((1)/(R) + (1)/(R)) = (2 (mu - 1))/( R)` `(1)/(f_a) = (2)/( R) ((mu_g)/(mu_a) -)` …(i) `(1)/(f_1) = (2)/(R)((mu_g)/(mu_l)-1)` ...(ii) Divide (i) by (ii), `(f_l)/(f_a)=(((mu_g)/(mu_a)-1 ))/(((mu_g)/(mu_l) - 1)) = (((1.5)/(1) -1))/(((1.5)/(1.7) - 1)) = (0.5)/(-0.2//1.7)` `f_l = (-0.5 xx 1.7)/(0.2) xx f_a = -4.25 xx 15 = -63.75 cm`. |
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| 976. |
A plano-convex lens `(mu = 1.5)` has a curved surface of radiys 15 cm. what is its focal length ? |
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Answer» Correct Answer - 30 cm |
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| 977. |
A double convex lens is made of glass of refractive index 1.5. If its focal length is 30 cm, then radius of curvature of each of its curved surface isA. 10 cmB. 15 cmC. 18 cmD. None of these |
| Answer» Correct Answer - d | |
| 978. |
A concave lens is placed in contact with a convex lens of focal length `25 cm`. The combination produces a real image at a distance of `80 cm`, when an object is at a distance of `40 cm`. What is the focal length of concave lens ?A. `-400 cm`B. `-200 cm`C. `+400 cm`D. `+200 cm` |
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Answer» Correct Answer - A For the combination of lens, Here, ` u=-40" cm ", v= +80" cm ", f=?` `therefore" "(1)/(f)=(1)/(80)-(1)/(-40)=(1+2)/(80)=(3)/(80)` Now, `(1)/(f)=(1)/(f_(1))+(1)/(f_(2))rArr(1)/(f_(2))=(1)/(f)-(1)/(f_(1))` `(1)/(f_(2))=(3)/(80)-(1)/(25)=(15-16)/(400)=(-1)/(400)rArrf_(2)=-400" cm "` |
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| 979. |
An astronomical telescope has a magnifying power 10. The focal length of eyepiece is 20 cm . The focal length of objective isA. `2 cm`B. `200 cm`C. `(1)/(2) cm`D. `(1)/(200) cm` |
| Answer» Correct Answer - b | |
| 980. |
A double convex lens `(R_(1) = R_(2) = 10 cm) (mu = 1.5)` having focal length equal to the focal length of a concave mirror. The radius of curvature of the concave mirror isA. `10 cm`B. `20 cm`C. `40 cm`D. `15 cm` |
| Answer» Correct Answer - b | |
| 981. |
The focal length of a concave-convex lens of radii of curvature 5 cm and 10 cm is 20 cm. what will be its focal length in water ? Given `.^(a)mu_(w) = 4//3`. |
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Answer» Correct Answer - `-80 cm` |
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| 982. |
A convex-concave diverging lens is made of glass of refractive index 1.5 and focal length 24 cm. radius of curvature for one surface is double that of the other. Then radii of curvature for the two surfaces are (in cm )A. 6,12B. 12,24C. 3,6D. 18,36 |
| Answer» Correct Answer - A | |
| 983. |
Assertion : The radius of curvature of a mirror is double of the focal length. Reason : A concave mirror of focal length f in air is used in a medium of refractive index 2. Then the focal length of mirror in medium becomes 2f.A. If both assertion and reason are true and reason is the correct explanation of assertion.B. If both assertion and reason are true and reason is not the correct explanation of assertion.C. If assertion is true but reason is false.D. If both assertion and reason are false. |
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Answer» Correct Answer - C Focal length of a mirror does not depend on the medium in which mirror is held. It depend on the radius of the sphere from which it is made. However focal length of a lens does depend on medium. |
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| 984. |
If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objectiveA. 100 cmB. 10 cmC. 20 cmD. 25 cm |
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Answer» Correct Answer - C (c ) Given, `f_(o)+f_(e)`=105 `f_(o)+f_(e)/20 = 105` `f_(o)=100 cm` `f_(o)+f_(e)=105 cmand f_(o/(f_(e))=20 cm` |
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| 985. |
A double convex lens (`R_(1)=R_(2)=10 cm`) having focal length equal to the focal length of a concave mirror. The radius of curvature of the concave mirrorA. 10 cmB. 20 cmC. 40 cmD. 15 cm |
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Answer» Correct Answer - B (b) we have, `1/f=(1.5-1)(1/10+1/10)` `therefore` Focal length, f= 10 cm Radius of curvaature, R=2f=20 cm |
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| 986. |
The radii of curvature of the two surfaces of a lens are 20 cm and 30 cm and the refractive index of the material of the lens is 1.5. If the lens is concave -convex, then the focal length of the lens isA. 24 cmB. 10 cmC. 15 cmD. 120 cm |
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Answer» Correct Answer - D (d) The focal length of the lens, `1/f=(mu-1)(1/R_(1)-1/R_(2))` `1/f=(1.5-1)(1/20-1/30)rArr1/f=0.5((30-20)/600)` `or1/f=1/2xx10/600=1/120` or The focal length, f = 120 cm |
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| 987. |
A concave and convex lens have the same focal length of 20 cm and are put into contact to form a lens combination. The combination is used to view an object of 5 cm length kept at 20 cm from the lens combination. As compared to the object, the image will beA. Magnified and invertedB. Reduced and erectC. Of the same size as the object and erectD. Of the same size as the object but inverted |
| Answer» Correct Answer - c | |
| 988. |
When a thin convex lens is put in contact with a thin concave lens of the same focal length (f), then the resultant combination has focal length equal toA. f/2B. 2fC. 0D. `oo` |
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Answer» Correct Answer - D (d) Resultant combination of focal length, `F_(comb)=(f_(1)f_(2))/(f_(1)+f_(2))=(f(-f))/(f+(-f))=oo` |
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| 989. |
A concave lens and a convex lens have same focal length of `20 cm` and both put in contact this combination is used to view an object `5 cm` long kept at `20 cm` from the lens combination. As compared to object the image will beA. Magnified and invertedB. Reduced and erectC. Of the same size and erectD. Of the same size and inverted |
| Answer» Correct Answer - c | |
| 990. |
A concave lens is kept in contact with a convex lens of focal length `20 cm`. The combination works as a converging lens of focal length `100 cm`. Calculate power of concave lens. |
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Answer» Correct Answer - `-4D` |
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| 991. |
White light is incident on the interface of glass and air as shown in figure. If green ligth is just totally internally reflected then the emerging ray in air contains A. yellow, orange ad red coloursB. violet, indigo and blue coloursC. All coloursD. All colours except green |
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Answer» Correct Answer - D White light is incident on face AB of a glass prism, the green light is just to tally internally reflected at fact AC, the light emerging from face AC will contain all colour except green. |
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| 992. |
An astronomical telescope uses lenses of power `10 D and `1 D`. What is its magnifying power in normal adjustment ? |
| Answer» `m = (f_0)/(f_e)=(P_e)/(P_0) = (10)/(1)`. | |
| 993. |
The magnifying power of an astronomical telescope is `5`. When it is set for normal adjustment, the distance between the two lenses is `24 cm`. Calculate the focal lengths of eye piece and objective lens. |
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Answer» Correct Answer - `4 cm ; 30 cm` Here, `m = 5, L = 24 cm, f_o = ?, f_e = ?` As `m = (f_o)/(f_e) = 5 :. f_o = 5 f_e` Also, in normal adjustment `L = f_o + f_e = 5 f_e + f_e = 6 f_e` `f_e = (L)/(6) = (24)/(6) = 4 cm` and `f_o = 5 f_e = 5 xx 4 cm = 20 cm`. |
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| 994. |
An astronomical telescope of magnifying power `7` consists of two thin lenses `40 cm` apart, in normal adjustment. Calculate the focal lengths of the lenses.A. 1080B. 200C. 30D. 186 |
| Answer» Correct Answer - c | |
| 995. |
A convex lens of focal length `5 cm` is used as a simple microscope. What will be the magnifying power when the image is formed at the least distance of distinct vision ? |
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Answer» Correct Answer - 6 Here, `f = 5 cm, d = 25 cm, m = ?` `m = (1 + d//f) = (1 + 25//5) = 6`. |
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| 996. |
Calculate the maximum magnifying power of a simple microscope consisting of a convex lens of focal length `5 cm`. Distance of distinct vision is `25 cm`. |
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Answer» Here, `f = 5 cm, m = ? d = 25 cm` Maximum magnifying power, `m = (1+(d)/(f)) = (1+(25)/(5)) = 6`. |
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| 997. |
Least distance of distinct vision is 25 cm . Magnifying power of simple microscope of focal length 5 cm isA. `1//5`B. 5C. `1//6`D. 6 |
| Answer» Correct Answer - d | |
| 998. |
A magnifying glass of focal length 5cm is used to view an object by a person whose smallest distance of distinct vision is 25cm. If he holds the glass close to eye, then the magnification isA. 5B. 6C. 2.5D. 3 |
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Answer» Correct Answer - B Given, f = 5 cm D = 25 cm `therefore` Magnification, `m=1+(D)/(f)` `m=1+(25)/(5)=6` |
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| 999. |
An object is placed at a distance u from a simple microscope of focal length f. The angular magnifiction obtaioned dependsA. on f but not on uB. on u but not on fC. on f as well as uD. Neither on f nor on u |
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Answer» Correct Answer - A The angular magnification obtained depends onb f but not on u. |
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| 1000. |
In a compound microscope, the intermediate image isA. virtual, erect and magnifiedB. real, erect and magnifiedC. real, inverted and magnifiedD. virtual, erect and reduced |
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Answer» Correct Answer - C In compound microcope, the intermediate image is real, inverted and magnified. |
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