Question

at what position an object be placed in front of a concave mirror of radius of curvature 40cm so that an erect image of magnification of 3 be produced ?

Answer 1

• C=40cm
• f=C/2=40/2=20

• m=3

$\\ \sf\longmapsto m=\dfrac{f}{f-u}$

$\\ \sf\longmapsto 3=\dfrac{20}{20-u}$

$\\ \sf\longmapsto 3(20-u)=20$

$\\ \sf\longmapsto 60-3u=20$

$\\ \sf\longmapsto 3u=40$

$\\ \sf\longmapsto u=13.3cm$

• m=magnification
• f is focal length
• C is radius of curvature
• u is object distance