when an object is placed 20cm away from a convex lens, No image is obtained on the Either side of the lens. what is the focal length of the lens? If the refractive index of the of the glass with respect to air is 1.5, what is the Refractive index of air, with respect to glass?
Answers
Answer:
Ans: As there is no image formed at either side of the lens so there is only one condition that is the object is placed at the focus of the lens.
Focal length of the lens is 20cm.
Refractive index of air with respect to glass
=refractive index of air/refractive index of glass
=1/1.5 =0.67
Or, The length of an object is 5cm. An image of length 10cm is obtained when it is placed at distance of 2cm in front of a convex lens. What is the linear magnification and image distance?
Ans: u =- 10 cm for convex mirror, the object distance is -ve.
v=?, R= 30 cm, f =15 cm, ho= 5 cm
1/u+1/v=1/f
(-1/10)+(1/v)=(1/15)
1/v=1/15+1/10
1/v=(2+3)/30
1/v =5/30
v= 6 cm
size of the image
m= hi/ho =- v/u
=- 6/10 =0.6
0.6=hi/5
hi=3 cm
The image is formed at a distance of 6 cm behind the mirror, virtual, upright and smaller than the object.
Size of the image is 3 cm.