Question

an object 5 cm high is placed at a distance of 20 cm in front of a concave mirror of focal length 15 cm. at what distance from the mirror should a screen be placed to get the sharp image also calculate the size of the image formed

Answer 1

Object-size, h = + 5.0 cm; Object-distance, u = – 20.0 cm; Focal length, f = –15.0 cm;Image-distance, v = ? Image-size, h′ = ?Mirror formula is             (1/v) + (1/u) = 1/f1/v = (1/f) − (1/u)       = (−1/15) + (1/20)       = −1/60 v = − 60 cm. The screen should be placed at 60 cm from the mirror. The image is real. Magnification m = h'/h = − v/u = 60/(– 20) = – 3 Height of the image h' = mh = (– 3)x5 = − 15 cm The image in inverted and enlarged. 

Answer 2

Answer:

Explanation:

Object-size, h = + 5.0 cm;

 Object-distance, u = – 20.0cm; 

Focal length, f = –15.0 cm;

Image-distance, v = ?

 Image-size, h′ = ?

Mirror formula is (1/v) + (1/u) = 1/f

1/v = (1/f) − (1/u)      

= (−1/15) + (1/20)      

= −1/60 

= − 60 cm. 

The screen should be placed at 60 cm from the mirror. The image is real. 

Magnification m = h'/h = − v/u

= 60/(– 20)

= – 3 

Height of the image h' = mh = (– 3)x5 = − 15 cm The image in inverted and enlarge