solution

 Screenshot-20221227-100443 Accordint to sign convention:

focal length (f) = –15cm

object distance (u) = –25cm

object height (ho ) = +4cm

image distance (v) = ?

image height (hi ) = ?

Substitute the above values in the equation

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

(1/-15)=(1/v)+ (1/-25) (1/v)= (1/25)-(1/15)

(1/v )= (-2/75)

-->v= -37.5cm

So the screen should be placed at 37.5cm from the pole of the mirror. The image is real.

magnification m = hi/h0 = -v/u

by substituting the above values hi/4=(-37.5)/(-25)

hi=-(35.5*4)/(25)

hi=-6cm

So, the image is inverted and enlarged.

We have learnt the phenomenon of reflection of light by curved mirrors. Let us make use of it in our daily life.

making a solar cooker

 You might have heard the story of Archimedes burning ships using mirrors. Can we at least heat up a vessel using a mirror?

Screenshot-20221227-100509 Let us try:

We have already learnt that a concave mirror focuses parallel sun rays at the focal point of the mirror. So with a small concave mirror we can heat up and burn paper as shown in the figure-23. (Try this with convex mirror also what do you observe?)


page no:15

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