Advertisements
Advertisements
Question
A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]
Options
\[f = R/2\]
- \[f = R\]
\[f = - R\]
\[f = 2R\]
Solution
f = R
As from lens maker formula:
\[\frac{1}{f} = (m - 1)(\frac{1}{R_1} - \frac{1}{R_2})\]
\[ \Rightarrow \frac{1}{f} = (1 . 5 - 1)(\frac{1}{R} - \frac{1}{- R}) (\text{ As given } R_1 = R_2 = R)\]
\[ \frac{1}{f} = (0 . 5)(\frac{1}{R} + \frac{1}{R})\]
\[ \frac{1}{f} = (0 . 5)(\frac{2}{R})\]
\[ f = R\]
APPEARS IN
RELATED QUESTIONS
Define the power of a lens.
Consider two statements A and B given below:
A: real image is always inverted
B: virtual image is always erect
Out of these two statements:
The power of a lens is + 0.2 D. Calculate its focal length.
The optician's prescription for a spectacle lens is marked +0.5 D. What is the:
(a) nature of spectacle lens?
(b) focal length of spectacle lens?
The focal length of a lens is +150 mm. What kind of lens is it and what is its power?
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
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 this combination converging or diverging?
Define the term focal length of a lens.
State the condition for the following a lens has both its focal lengths equal .
How is the power of a lens related to its focal length?
A symmetric double convex lens in cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4 D, the power a cut-lens will be
A double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double of the other. Find the radii, if the refractive index of the material of the lens is 1.5.
Surabhi from std. X uses spectacle. The power of the lenses in her spectacle is 0.5 D.
Answer the following questions from the given information:
- Identify the type of lenses used in her spectacle.
- Identify the defect of vision Surabhi is suffering from.
- Find the focal length of the lenses used in her spectacle.
The power of the magnifying glass depends on the distance of the magnifying glass from object.
What is power of accommodation of eye?
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
A convex lens with radii of curvature R1 = R2 is immersed in water. Assuming that the refractive indices of glass and water are 3/2 and 4/3 respectively, its focal length f1 in comparison to that in air, f, is ______.
An object is kept at a distance of 1m from a lens of power +2D:
- Identify the type of lens.
- Calculate its focal length and distance of the image formed.
