Question

a dentist mirror has a radius of curvature of 3 cm .How far must it be placed from the small dental cavity to give a virtual image of the cavity that is magnified 5 times ?

Answer 1

R = 3cm,

f =- 3/2 = -1.5cm ( Negative sign for cancave mirror)

m = 5

We know that m= - v/u

Therefore (-5u) =( v)

Using (1/v) + (1/u) = (1/f )

(1/-5u) + ( 1/u) = (1/-1.5)

Therefore, (5u /4) = -1.5

Thus, u = -1.2 cm

The object should be placed at a distance of 1.2cm from the mirror to get 5 times magnified image.

Answer 2

hope this helps u

Given ;

R = -3 cm

r=2f

f=r/2

f = -1.5 cm

m = -v/u

5 = -v/u

5u = -v

----------------------------

Using mirror formula;

1/f = (1/v)+(1/u)

(-1/1.5) = (-1/5u) + (1/u)

(-10/15) = (-1+5)/5u

-2/3 = 4/5u

-10u = 12

u = -12/10

u = -1.2cm

by hariprasath @rukumanikumaran