Question

Q.4 A concave mirror of focal length 20 cm forms an image twice the size of the object. For the virtual position of
the object, the position of the object will be at:
(a) 25 cm
(b) 40 cm
(c) 10 cm
(d) At infinity​

Answer 1

Answer: is 10

Explanation:

hello friend..!!

according to the given question , we know that the mirror formula is 

1/f = 1/v + 1/u ---------(1)

where f → focal length = -20 cm

v → image distance 

u→object distance 

now, according to the given question ,

hi / ho = - V/U = 2 

⇒ hi = 2ho also v = -2u 

since we got v = -2u -----(2)

now by substituting equation (2) in (1) gives 

⇒ -1/20 = -1/2u + 1/u

⇒ -1/20 = -1 + 2 / 2u

⇒ -1/20 = 1/2u 

⇒ 2u = - 20 

⇒ u = -10 cm 

Answer 2

Answer:

is 10

Explanation:

Refer the attachment