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Optics

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12 Feb 2009 21:36:29 IST

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1207

Ray Optics : MCQ

None

1.) Convex lens is immersed from air into water, its focal length will ...................

[A]increase. [B]decrease.

[C]not change. [D]none of above.

2.) A plane mirror is approaching you with a velocity of 10 cm/s. With what velocity is your image in it is approaching you?

[A]10 cm/s [B]20 cm/s

[C]30 cm/s [D]-20 cm/s

3.) Focal length and refractive index of a plano-convex lens of glass are f and 1.5 respectively . If its radius of curvature is R, relation between f and R is .......................

[A] f= R/2. [B] f= 2R.

[C] f=3R /2. [D] f=R.

4.) If the focal length for convex lens for red, green, blue colours are f_{r ,}f_{g ,}f_b respectively, which statement is true from the following ?

[A] f_r< f_b [B]f_g < f_r

[C]f_b < f_r [D]f_r= f_g = f_b

5.) Refractive index of a plano-convex lens is 1.5, if its radius of curvature is 50 cm, the power of plano - convex lens is...............................

[A] -1.0 D. [B] -0.5 D

[C] +1.0 D [D]+0.5 D

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Comments (4)

10904him

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Joined: 29 Dec 2006

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12 Feb 2009 21:40:18 IST

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1-When dipped in water relative refractive index decreases and hence focal length increases----by lens formula.

10904him

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Posts: 191

12 Feb 2009 21:45:25 IST

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2-If it moves a distance x towards me my image comes 2x towards me hence it approaches me at 20m/s.2-f=R---by lens formula4-f is inversely proportional to refractive index (not exactly)thus you can decide the order as Ub>Ug>Ur -U is refractive index.

Ankit

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13 Feb 2009 09:58:36 IST

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2. ans b) 20cm/s

3.f=2R

apply lens maker's formula

5. ans c) 1.0 D

again apply lens amker's formula then P= 1/f

akshay A NEW BEGINNING...

Blazing goIITian

Joined: 25 Dec 2007

Posts: 1104

14 Feb 2009 11:22:31 IST

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ans 1 - Ause lens formula ans 2 - Bans 3 -Blens makers formulaans 4- A ans 5 -Cuse p =1/f.

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