A convex lens from a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle be placed in front of the convex lens if the image is equal to size of the object? Also, find the power of the lens?

Explanation

Here image distance = `+50` cm
v = 50 cm
m = 1
`P = 1/f = ? `
for real image by lens .
`m = v/u`
`1 = v/u`
` :. " u = - 50 cm `
` :. ` Object distance = 50 cm .
Now, `1/u- 1/u = 1/f`
` rArr 1/50 - 1/(-50) = 1/f`
`rArr " "(1+1)/50 = 1/f`
`f = 25 cm `
`P = 1/((25/100m) = 1/(1/4)`