First slide
Ray optics

An object is placed at a distance of 40cm from a concave mirror of focal length 15cm. If the object is displaced through a distance of 20cm towards the mirror, the displacement of the image will be



Using mirror formula,

1f=1v1+1u;-115=1v1-1401v1=1-15+140v1=-24 cm

When object is displaced by 20 cm  towards mirror. 

Now,u2=-20 cm

1f=1v2+1u2;1-15=1v2-1201v2=120-115v2=-60 cm

So, the image will be shift away from mirror by (60-24)cm=36 cm


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