A student focused the image of a distant object using a device 'X' on a white screen 'S' as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device.

The device X is a convex lens of focal length 20 cm.

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The device X is a concave mirror of focal length 40 cm.

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The device X is a concave mirror of radius of curvature 40 cm.

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The device X is a convex lens of focal length 40 cm.

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Solution

The correct option is A The device X is a convex lens of focal length 40 cm.
As the image is focused on the screen placed behind the device X, thus device X is a lens but cannot be a mirror.
Also convex lens always forms the image of the distant object at its focus. Thus device X must be a convex lens of focal length 40 cm.

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Similar questions

A student focused the image of a distant object using a device 'X' on a while screen 'S' as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device

Q. A student used a device (X) to obtain/focus the image of a well illuminated distant building on a screen (S) as shown below in the diagram. Select the correct statement about the device (X).

(a) This device is a concave lens of focal length 8 cm.
(b) This device is a convex mirror of focal length 8 cm.
(c) This device is a convex lens of focal length 4 cm.
(d) This device is a convex lens of focal length 8 cm.

Q. Study the given ray diagrams and select the correct statement from the following :

(a) Device X is a concave mirror and device Y is a convex lens, whose focal lengths are 20 cm and 25 cm respectively.
(b) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 10 cm and 25 cm respectively.
(c) Device X is a concave lens and device Y is a convex mirror, whose focal lengths are 20 cm and 25 cm respectively.
(d) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.

Q. A student determines the focal length of a device X, by focussing the image of a far off object on the screen positioned as shown in the figure alongside.

The device X is a :
(1) Convex lens
(2) Concave lens
(3) Convex mirror
(4) Concave mirror

Q. A convex lens of focal length

40 c m

is held at a distance

12 c m

coaxially above a concave mirror of focal length

18 c m

. If the convex lens is replaced by a concave lens of focal length

60 c m,

it gives rise to an image coincident with itself. Then the object distance

d

is :

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