Question

10. Explain the relation between these two pair of words with respect to lenses.
a) focal length and center of curvature.
b) Focal length and power of lens.
c) magnification of a lens and height of object and image.
-OR-
(i) differentiate between real and virtual image.
(ii) On what factors does refractive index depends.​

Answer 1

Answer:

Hope it helps you.

Answer 2

a) Focal length and centre of curvature

• The distance from the optical centre of the lens to the focal point (F) on the principal axis is called Focal length.
• Centre of curvature is the centre of the sphere of which the lens is a part.
• Relation between Focal length and centre of curvature:
• f = C/2;    f is focal length and C is centre of curvature.

b) Focal length and power of the lens.

• Power of lens is defined as the reciprocal of the focal length.
• Power = 1/f

c) Magnification of a lens and height of object and image.

• Magnification of a lens is defined as the ratio of the height of an image to the height of the object.
• Magnification = height of image /  height of object.

                                         

                                                   or

(i)Differentiate between real and virtual images.

• Real image

1. Formed by the actual meeting of the light rays at a point.
2. Can be obtained on the screen.
3. Real image is inverted.

• Virtual image

1. Light rays appear to meet to form a virtual image.
2. Cannot be obtained on the screen.
3. Virtual image is erect.

(ii) Factors on which refractive index depends.​

• Ratio of speed of light in a vacuum to speed of light in substance.
• μ = c/v
• Refractive index depends on:

1. Wavelength- the light of different wavelengths refracts to different extents.
2. Temperature- velocity of light in medium increases with an increase in temperature, thus refractive index decreases.
3. Viscosity- Refractive index is inversely proportional to viscosity.

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