Correct option is B
Ans. (b) -6/5
Sol. The magnification produced by a lens is given by the formula:
M=Image height/Object height =Image distance/Object distance
Here;
- Object distance, u=−25cmu = -25 \, \text{cm}u=−25cm (it is taken as negative because object is on opposite side of image).
- Image distance, v=30cmv = 30 \, \text{cm}v = 30 cm (positive because the image is real).
Using the magnification formula:
Thus, the magnification is M=−65M = -\frac{6}{5}M=
(v/u) = (30/-25)= -6/5(negative sign indicates that the image is inverted).
Important Key Points:
- Magnification of a lens is negative for real and inverted images, as opposed to positive for virtual and upright images.
- The object and image distances are measured from the lens, with object distance being negative for real objects and positive for virtual ones.
- A positive image distance indicates that the image is real and formed on the opposite side of the object.
- The magnification value directly relates to the size of the image compared to the object; a magnification greater than 1 indicates an enlarged image.
- In this case, the image is real, inverted, and 6/5 times the size of the object.
- The magnification produced by lenses not only depends on the object and image distances but also affects the orientation and size of the image formed.
- Real images formed by converging lenses are always inverted and can be projected on a screen, unlike virtual images, which cannot be projected.
- Sign conventions in optics are crucial: distances measured against the direction of light propagation are negative, while those along the light path are positive.
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