Question

An object of size 10 cm is kept at a distance of 10 cm from a convex lens. If the focal length of the lens is 5 cm, the size of the image is

Answer 1

Answer:

10 cm

Explanation:

given ,   u = - 10 cm

             f = 5 cm

len's formula,

      1/f  =  1/v - 1/u

      1/5 =  1/v - ( 1/ -10 )

      1/v =  1/5 - 1/10

      1/v = 1/10

thus ,  v = 10 cm

    h' / h  =  v / u

    h' / -10 =  10 / -10

  thus ,----------- h' = 10 cm -------------

Answer 2

Answer:

Distance of image (v) = 10 cm from lens

Size of the real image = 10 cm

Explanation:

Given that:

Distance of image (v) = ?

Distance of Object (u) = -10 cm

The object and image will be at different sides of Convex lens.

That's why let the distance of object is -ve for getting image at +ve side.

Size of object = 10 cm

Focal length of the lens (f) = 5 cm

We know that;

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u} \: ...equation(i) \\ or \: \frac{1}{v} = \frac{1}{u} + \frac{1}{f} \\ or \: v = \frac{uf}{f + u} \: ...equation(ii)$

So, Putting the values of u and f we get;

$v = \frac{5 \times - 10}{ - 10 + 5} \: cm \\ v = \frac{ - 50}{ - 5} \: cm \\ v = 10 \: cm$

So the distance of image (v) = 10 cm from lens

And this is a real image.

And Magnification formula of lens;

$m = \frac{v}{u}$

So here we get ;

$|m| = \frac{10}{10} \\ |m| = 1$

So the image and object is same in size.

Size of the real image = 10 cm