Question

f=30cm and v=45what the value of u

Answer 1

Hey there !

Here's the answer !

According to the mirror rule,

1 / v + 1 / u = 1 / f

So we are given with v ( Image distance ) and f ( Focal length ). We need to find u ( Object distance ).

Substituting the values in the formula we get,

1 / 45 + 1 / u = 1 / 30

=> 1 / u = 1 / 30 - 1 / 45

=> 1 / u = 45 - 30 / 45 * 30 [ LCM ]

=> 1 / u = 15 / 1350

=> 1 / u = 1 / 90 [ Simplifying the fraction above ]

Taking reciprocals we get,

u = 90 cm

Hence the value of object distance ' u ' is 90 cm.

Hope my answer helped !

Answer 2

1/u = 1/f -1/v

therefore,

u=( v *f)/v-f

= (45 * 30)/ 45 - 30

= 1350/15

= 90 cm

hope this helps you