1
Question
A concave mirror gives an image three times as large as the object placed at a distance of 20 cm from it. For the image to be real, the focal length should be.
A concave mirror gives an image three times as large as the object placed at a distance of 20 cm from it. For the image to be real, the focal length should be.
Open in App
Solution
The correct option is A 15 cm
Since the image formed by concave mirror is real ,so it must be an inverted image. Distance of object from mirror u=−20cmSince image is inverted then the magnification will be negative ,hence m=−3Magnification m=−3=−vu m=−3=−v−20
v=−60cmwe know for mirror1f=1v+1u1f=1−60+1−20
1f=−60−2060×20=−801200=−115
f=−15cm
Since the image formed by concave mirror is real ,so it must be an inverted image.
Distance of object from mirror u=−20cm
Since image is inverted then the magnification will be negative ,hence m=−3
Magnification m=−3=−vu
m=−3=−v−20
v=−60cm
we know for mirror
1f=1v+1u
1f=1−60+1−20
1f=−60−2060×20=−801200=−115
f=−15cm
Suggest Corrections
0
Similar questions
Join BYJU'S Learning Program
Explore more
Join BYJU'S Learning Program
