Find the focal length of the lens if the power of the lens is – 2D
A) 49 cm
B) 50 cm
C) 52.5 cm
D) 55 cm
1 Answers
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The distance between two focal points of a thin lens having focal length f is ………………
Correct option is C) 2f
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When a lens of focal length f is cut in to two equal halves perpendicular to principal axis, then the focal length of each part of the lens is ………………
Correct option is B) double
2 Answers 1 views
A convex lens of focal length 20 cm is cut into two halves along principal axis then focal length of each part will be …………………
Correct option is A) 20 cm
2 Answers 1 views
A convex lens of focal length 20 cm is cut into two halves perpendicular to the principal axis then focal length of each part will be ……………….
Correct option is C) 40 cm
2 Answers 1 views
If a person uses a lens of -2.5 D power, then the focal length of the lens is ……………………
Correct option is C) -40 cm
2 Answers 1 views
A doctor advised to use 4D lens. The focal length of the lens is ……………………..
Correct option is A) 25cm
2 Answers 4 views
A doctor has advised to use 2.5D lens. The focal length of the lens is …………………..
Correct option is A) 40 cm
2 Answers 1 views
A convex lens has focal length of 2.0 cm. Find its magnifying power if image is formed at DDV.
Given: f = 2 cm, v = D = 25 cm To find: Magnifying power (M.P.) Formula: M.P = 1 + \(\frac{D}{f}\) Calculation: From formula, M.P = 1 + \(\frac{25}{2}\) M.P. = 1 + 12.5 = 13.5
2 Answers 71 views
Two convex lenses of an astronomical telescope have focal length 1.3 m and 0.05 m respectively. Find the magnifying power and the length
Given: f0 = 1.3 m, fe = 0.05 m To find: i. Magnifying power of telescope (M.P.) ii. Length of telescope (L) Formulae: i. M.P = \(\frac{f_0}{f_e}\) ii. L = f0 + fe Calculation: From formula (i), M.P = \(\frac{1.3}{0.05}\) = 26 From formula (ii), L...
2 Answers 7 views
A point object O is placed on the principle axis of a convex lens of focal length 10 cm at 12 cm from the lens.
U = -12 f = -10 1/v - 1/u = 1/f 1/v + 1/12 = 1/10 1/v = 1/60 \(-\frac{1}{v^2} \)dv or \(\frac{1}{u^2} \)du du = \(\frac{v^2}{u^2} \)du \( \frac{v}{u} \)= same path △u1 = △u2 = 1mm △u1 = △v2 △v2 = vf - vi x2 = △v2 + 1mm x2...
2 Answers 1 views