An object is placed 21 cm in front of a concave mirror of radius of curvature 10cm. A glass slabe of thickness 3cm and refractive index 1.5 is then placed close to the irror in the space between the object and the mirror. The distance of the near surface of the slabe from the mirror is 1cm. The final image from the mirror will be formed at

Explanation

Shift by glass slab `=3(1-1//3//2)=1cm`
The mirror is shifted by `1cm` towards slab.
Distance of object from vertical mirror `=20cm`
Image by virtual concave mirror
`u=-20cm, f=-5cm, v=?`
`1/v+1/u=1/f`
`1/v+(1)/(-20)=(1)/(-5)`
`1/v=-1/5+(1)/(20)=(-4+1)/(20)`
`v=-(20)/(3)cm`
Distance of I from original mirror
`=20/3+1=(23)/(3)cm`