Advertisements
Advertisements
प्रश्न
An unsymmetrical double convex thin lens forms the image of a point object on its axis. Will the position of the image change if the lens is reversed?
Advertisements
उत्तर
Thin lens formula: `1/v - 1/u = 1/f`
For a given object position if focal length of the lens does not change, the image position remains unchanged.
By lens maker's formula,
`1/f = (mu - 1) (1/R_1 - 1/R_2)`
For this position R1 is positive
And R2 is negative. Hence focal length at this position
`1/f_1 = (mu - 1) (1/((+ R_1)) - 1/((-R_2))) = (mu - 1)(1/R_1 + 1/R_2)`
Now the lens is reversed,
At this position R2 is positive and R1 is negative. Hence focal length at this position is
`1/f_2 = (mu - 1) (1/((+ R_2)) - 1/((-R_1))) = (mu - 1)(1/R_1 + 1/R_2)`
We can observe the focal length of the lens does not change in both positions, hence the image position remains unchanged.
APPEARS IN
संबंधित प्रश्न
A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is
- a convex lens of focal length 20 cm, and
- a concave lens of focal length 16 cm?
An object of size 3.0 cm is placed 14 cm in front of a concave lens of focal length 21 cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?
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 card sheet divided into squares each of size 1 mm2 is being viewed at a distance of 9 cm through a magnifying glass (a converging lens of focal length 9 cm) held close to the eye.
- What is the magnification produced by the lens? How much is the area of each square in the virtual image?
- What is the angular magnification (magnifying power) of the lens?
- Is the magnification in (a) equal to the magnifying power in (b)? Explain.
Figure shows an equiconvex lens (of refractive index 1.50) in contact with a liquid layer on top of a plane mirror. A small needle with its tip on the principal axis is moved along the axis until its inverted image is found at the position of the needle. The distance of the needle from the lens is measured to be 45.0 cm. The liquid is removed and the experiment is repeated. The new distance is measured to be 30.0 cm. What is the refractive index of the liquid?
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.
The point on the principal axis where rays parallel to the principal axis actually meet after refraction, or appear to diverge after refraction, is called the:
Which of the following is the correct Thin Lens Formula?
According to the new Cartesian sign convention for lenses, the focal length of a convex lens is:
According to the new Cartesian sign convention used for lenses, distances measured opposite to the direction of incident light are taken as:
A ray of light passing through the optical centre of a thin lens:
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:
Using the sign convention with \[OB = -u\] and \[DI = +v\] in the combined refraction equation for a thin lens gives:
A lens with an infinite focal length behaves like:
Magnification produced by a lens is positive when the image is:
A concave lens is used in spectacles for myopia because it:
