A concave mirror converges light rays from the sun at 10 cm from the mirror. If an object is placed 20 cm from the mirror, the image is formed:

Correct option is D

Sol: The correct answer is (d) 20 cm in front of the mirror

Given:

Focal length: $$f$$ = 10 cm

​Object distance: $$u$$ = -20 cm

Formula used:

​$$\frac{1}{f}= \frac{1}{u}+ \frac{1}{v}$$

Where:

​$$f$$ : focal length of the mirror (positive for concave mirrors),

$$u$$: object distance (negative if on the same side as the mirror),

$$v$$ : image distance (positive for real images in front of the mirror).

Solution:

​$$\frac{1}{10}$$ = $$\frac{1}{-20}$$ + $$\frac{1}{v}$$

$$\frac{1}{v}$$ = $$\frac{1}{10}- \frac{1}{20}$$

Take the LCM of 10 and 20:

$$\frac{1}{v}$$ = $$\frac{2}{20}- \frac{1}{20} = \frac{1}{20}$$

$$v$$ = 20cm

Since  $$v >0,$$​ the image is formed in front of the mirror (real and inverted).

Thus, the correct answer is:

20 cm in front of the mirror