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Question
- Virtual, upright and magnified
- Real, inverted and magnified
- Real, inverted and diminished
- All of the above
Convex mirror forms virtual image, diminished and upright image.
The correct answer is: All of the above
- The convex mirror will not form a real image.
- Convex mirrors will not produce a magnified image of an object.
- Convex mirrors will always produce an upright image.
- So, the correct option is d.
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) a convex lens of a focal length 20 cm, and (b) a concave lens of focal length 16 cm?
Here, the point P on the right of the lens acts as a virtual object.
Object distance, u = 12 cm
Focal length, f = 20 cm (a) Using the lens formula, 1v =1f+1u∴ 1v =120+112 =3+560 =860
i.e., v = 60/8 = 7.5 cm.
Image is at a distance of 7.5 cm to the right of the lens, where the beam converges. (b)Now,Focal length of concave lens, f = –16 cmObject distance, u = 12 cm
∴
1v=1f+1u =-116+112 = -3+448 =148
⇒ v = 48 cm
Hence, the image is at a distance of 48 cm to the right of the lens, where the beam would converge.
Text Solution
Solution : From mirror formula <br> `(1)/(v)+(1)/(u)=(1)/(f) rArr(1)/(v)=(1)/(f)-(1)/(u)` <br> For convex mirror, <br> Object distance `u` is negative and the focal length `f` is positive. <br> `therefore (1)/(v)=(1)/(+f)-(1)/(-u)=(1)/(f)+(1)/(u)` <br> Therefore, the image distance is always positive incase of a convesx mirror. <br> Hence, the convex mirror always formed a virtual image.