Advertisements
Advertisements
प्रश्न
Two concave lenses L1 and L2 are kept in contact with each other. If the space between the two lenses is filled with a material of smaller refractive index, the magnitude of the focal length of the combination
पर्याय
becomes undefined
remains unchanged
increases
decreases.
Advertisements
उत्तर
increases
The focal length of the combination will increase. For finding out the combination of lens we have the formula:
\[\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2} - \frac{d}{f_1 f_2}\]
Where, F is the focal length for the combination
d is the separation between two lenses
Here, d = 0
\[\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}\]
\[ F = \frac{f_1 f_2}{f_1 + f_2}\]
Hence, the focal length will increase.
APPEARS IN
संबंधित प्रश्न
A screen is placed 90 cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20 cm. Determine the focal length of the lens.
A man with normal near point (25 cm) reads a book with small print using a magnifying glass: a thin convex lens of focal length 5 cm.
(a) What is the closest and the farthest distance at which he should keep the lens from the page so that he can read the book when viewing through the magnifying glass?
(b) What is the maximum and the minimum angular magnification (magnifying power) possible using the above simple microscope?
An equiconvex lens of focal length 'f' is cut into two identical plane convex lenses. How will the power of each part be related to the focal length of the original lens ?
Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without loosing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.
Answer the following question.
An optical instrument uses a lens of 100 D for the objective lens and 50 D for its eyepiece. When the tube length is kept at 20 cm, the final image is formed at infinity.
(a) Identify the optical instrument.
(b) Calculate the magnification produced by the instrument.
A transparent refracting medium bounded by two surfaces, of which at least one is spherical, is called a:
The straight line passing through the optical centre and the centres of curvature of the lens surfaces is called the:
The distance between the optical centre and the principal focus is called the:
The ratio of the height of the image to the height of the object is called:
Which of the following correctly represents the Lens Maker's Formula?
In the Lens Maker's Formula, the symbols \[R_1\] and \[R_2\] denote:
Which of the following is the correct Thin Lens Formula?
According to the new Cartesian sign convention for lenses, the focal length of a concave lens is:
According to the new Cartesian sign convention for lenses, heights measured below the principal axis are taken as:
A ray parallel to the principal axis, after refraction through a convex lens, passes through:
A ray parallel to the principal axis, after refraction through a concave lens, appears to diverge from:
A ray directed towards the principal focus of a concave lens, after refraction, emerges:
A lens with an infinite focal length behaves like:
