Question

Focal length of concave lens is 10cm where should a real object be placed in front of it,where a magnification of 1/4 is formed

Answer 1

object must be placed 30 cm before the lens.
negative sign represent that it is before the lens.

Answer 2

Answer:u =30

Explanation:

given,

m=1/4

f=–10cm

We know, m=v/u

Now, 1/4=v/u

u=4v

Now,by lens' formula

1/f=1/v–1/u

1/(–10) =1/v – 1/4v

1/(–10)=(4–1)/4v

1/(–10)= 3/4v

4v= 3×(–10)

4v= (–30)

V=(–30)/4

Now;

U=4v

U= 4×(–30)/4

U=(–30)

Negative sign shows that the image is formed in front of it.