Question

the focal length of a concave mirror is 20cm. An object 5cm in size is placed 25cm in front of it. At what distance from the mirror should a screen be placed in order to obtain a sharo image.​

Answer 1

Answer:

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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

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Answer 2

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