A convex lens forms an image at a distance 10 cm when a parallel beam...
Explanation:
When a parallel beam of light is incident on a convex lens, the image is formed at the focal point on the other side of the lens. In this case, the image is formed at a distance of 10 cm from the lens.
To find the position of a concave mirror that would form the final image at infinity, we can use the mirror formula:
1/f = 1/v - 1/u
Where:
f = focal length of the mirror
v = image distance from the mirror
u = object distance from the mirror
a) At a distance of 10 cm from the lens:
The image formed by the convex lens is at a distance of 10 cm from the lens, which means the image distance (v) is -10 cm (negative sign indicates that the image is formed on the opposite side of the object). The object distance (u) is considered positive since the object is on the same side as the lens. We need to find the focal length (f) of the concave mirror.
Using the mirror formula:
1/f = 1/v - 1/u
1/f = 1/-10 - 1/10
1/f = -1/10 - 1/10
1/f = -2/10
f = -10/2
f = -5 cm
The negative value of the focal length indicates that the concave mirror is a diverging mirror.
b) At a distance of 15 cm from the lens:
Using the same approach as above, the image distance (v) is -15 cm and the object distance (u) is +15 cm. We need to find the focal length (f) of the concave mirror.
Using the mirror formula:
1/f = 1/v - 1/u
1/f = 1/-15 - 1/15
1/f = -1/15 - 1/15
1/f = -2/15
f = -15/2
f = -7.5 cm
Again, the negative value of the focal length indicates that the concave mirror is a diverging mirror.
c) At a distance of 5 cm from the lens:
Using the same approach as above, the image distance (v) is -5 cm and the object distance (u) is +5 cm. We need to find the focal length (f) of the concave mirror.
Using the mirror formula:
1/f = 1/v - 1/u
1/f = 1/-5 - 1/5
1/f = -1/5 - 1/5
1/f = -2/5
f = -5/2
f = -2.5 cm
Again, the negative value of the focal length indicates that the concave mirror is a diverging mirror.
d) Both (a) and (b):
From the calculations in parts (a) and (b), we can see that both the concave mirrors with focal lengths of -5 cm and -7.5 cm can form the final image at infinity. Thus, the correct answer is option 'D' - Both (a) and (b).
A convex lens forms an image at a distance 10 cm when a parallel beam...
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