Question

u=35,v=?,f=20 calculate the missing value of convex lens​

Answer 1

According to convex lens,

given :-

u = -35 units (object distance is always negative no matter which mirror or lens it is)

f = 20 units (since focal length is positive in convex lens)

v = ?

here we've to find the image distance (v)

using lens formula :- 1/v - 1/u = 1/f

➡ 1/v = 1/f + 1/u

➡ 1/v = (u + f)/fu

➡ v = fu/(u + f)

putting values,

➡ v = (20 × -35)/(-35 + 20)

➡ v = -700/-15

➡ v = 46.6 units (approximately)

hence, the image distance is 46.6 units

Answer 2

Using formula :-

1/v - 1/u = 1/f

1/v = 1/f + 1/u

1/v = (u + f)/fu

v = fu/(u + f)

Adding values:-

v = (20 × -35)/(-35 + 20)

v = -700/-15

v = 46.6

Answer is 46.6