A 7-cm tall candle is placed 105-cm from a lens with a focal length of +35-cm. H

Question

A 7-cm tall candle is placed 105-cm from a lens with a focal length of +35-cm. How far from the lens will the image be? cm. How tall will the image be? cm Which of the following describes the image? Choose all that apply. Real virtual upright inverted Now, imagine that the candle is moved closer, so that it is only 14-cm from the lens. How far from the lens will the image be? cm. How tall will the image be? cm Which of the following describes the image? Choose all that apply. real virtual upright inverted

Explanation / Answer

object distance s = 105 cm , size of candle = 7 cm, focal length f = 35 cm,
   from relation 1/s + 1/s' = 1/f ==> 1/s' = 1/f - 1/s
                          = 1/35 - 1/105
                       s' = 52.5 cm

its a real image ,inverted image , lateral magnification m = -s'/s= y'/y =>y'=-52.5/105*7 = -3.5

       image is diminished .

when s = 14 cm

   1/s + 1/s' = 1/f ==> 1/s' = 1/f - 1/s
                          = 1/35 - 1/14
                       s' = -23.33 cm

image height from lateral magnification m = -s'/s = - (-23.33)/14*7 =1.67*7= 11.69

here image is virtual image and the enlarged upright image

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