A student wants to project the image of a candle flame on a screen 90 cm in front of a mirror by keeping the flame at a distance of 15 cm from its pole.
(a) Suggest the type of mirror he should use.
(b) Determine the linear magnification in this case.
(c) Find the distance between the object and its image.
(d) Draw ray diagram to show the image formation in this case.
a) Concave mirror should be used inorder to project the flame of the candle.
b) Linear magnification of the concave mirror is,
c) Distance between the object and the image = 90 - 15 = 75 cm
d) The image formation is as shown below:
In order to locate the image, any two rays can be chosen.
i) a ray which is parallel to the principal axis, after reflection will pass through the principal focus in case of a concave mirror and diverge from the principal axis in case of a convex mirror.
ii) A ray passing through the principal focus will emerge parallel to the principal axis after reflection.
When an object is placed between the centre of curvature and focus of a concave mirror, the ray diagram is as shown below:
A 4 cm tall object is placed on the principal axis of a convex lens. The distance of the object from the optical centre of the lens is 12 cm and its sharp image is formed at a distance of 24 cm from it on a screen on the other side of the lens. If the object is now moved a little away from the lens, in which way (towards the lens or away from the lens) will he have to move the screen to get a sharp image of the object on it again? How will the magnification of the image be affected?
Given that,
Object distance, u = −12 cm
Image distance, v = 24 cm
The focal length of the lens is 8 cm.
Now if the object is moved away from the lens, the screen has to be moved towards the lens. This is because when we move the object away from the lens, the object distance is increased. Hence, by the lens formula, the image distance decreases.
Magnification is given as,
Since, the image distance (v) decreases, the value of magnification also decreases.
Draw a ray diagram to show the path of the refracted ray in each of the following cases:
A ray of light incident on a concave lens is:
(i) passing through its optical centre.
(ii) parallel to its principal axis.
(iii) directed towards its principal focus.
For a concave lens,
i) The ray diagram for a ray of light passing through the optical centre of the concave lens will emerge without any deviation.
The image will be placed between pole P and focus F for magnified and erect image.
For magnified and inverted image the object is placed either at focus or in between F and C.
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