Question

Please give me theanswer of ques.no.7

Answer 1

Let U be the position of an object and V be the position of an image.

Then,

U = ?

V = ?

Also suppose that, h₁ and h₂ be the height of object and height of image respectively.

Then, according to the given condition, the height of image is half of the height of object.

Therefore, h₂ = h₁ / 2

Also, we know that, 

- V / U = h₂ / h₁

- V / U = (h₁ / 2) / h₁

- V / U = 1 / 2

2 V = - U  

V = - U / 2   ......... (1)

Now we use the mirror formula,

1 / V + 1 / U = 1 / f

1 / V + 1 / U = 2 / R

1 / (-U/2) + 1 / U = 2 / R  ,   Using equation (1)

- 2 / U + 1 / U = 2 / 40

- 1 / U = 1 / 20

U = - 20 cm

Now,

V = - U / 2 = - (-20) / 2

V = 10 cm