Question

The lenses forms different types of images when object placed at different locations. When a ray is incident parallel to the principal axis, then after refraction, it passes through the focus or appears to come from the focus.When a ray goes through the optical centre of the lens, it passes without any deviation.
If the object is placed between focus and optical center of the convex lens, erect and magnified image is formed. As the object is brought closer to the convex lens from infinity to focus, the image moves away from the convex lens from focus to infinity. Also the size of image goes on increasing and the image is always real and inverted. A concave lens always gives a virtual, erect and diminished image irrespective to the position of the object.
(i) The location of image formed by a convex lens when the object is placed at infinity is
(a) at focus (b) at 2F
(c) at optical center (d) between F and 2F
(ii) When the object is placed at the focus of concave lens, the image formed is
(a) real and smaller (b) virtual and inverted
(c) virtual and smaller (d) real and erect
(iii) The size of image formed by a convex lens when the object is placed at the focus of convex lens is
(a) small (b) point in size
(c) highly magnified (d) same as that of object
(iv) When the object is placed at 2F in front of convex lens, the location of image is
(a) at F (b) at 2 F on the other side
(c) at infinity (d) between F and optical center
plz answer

Answer 1

Answer:

(i) answer = (a)

(ii) answer = (c)

(iii) answer = (c)

(iv) answer = (b)

Explanation:

Answer 2

(i)  The location of image formed by a convex lens when the object is placed at infinity is  (a) at focus.

(ii) When the object is placed at the focus of concave lens, the image formed is (c) virtual and smaller.

(iii) The size of image formed by a convex lens when the object is placed at the focus of convex lens is (c) highly magnified.

(iv) When the object is placed at 2F in front of convex lens, the location of image is  (b) at 2F on the other side.

Explanation:

• Focus is a point on principal axis where rays parallel to principal axis and coming from infinity converge or diverge.
• Focal length of spherical lens is half of the radius of curvature.
• Concave lens is a diverging lens. It possesses at least one surface that is curved inwards. It is thinner at its centre than at its edges.
• Convex lens is a converging lens. It possesses at least one surface that is curved outwards. It is thinner at its edges than at its centre.

Concave lens:

• Object between infinity to optical centre - Image is between Focus and optical centre and is diminished, virtual and erect.
• Object at infinity - Image is highly diminished, virtual and erect.

Convex lens:

• Object at infinity - Image at focus, highly diminished, real and inverted.
• Object at focus - Image at infinity, image is highly magnified, real and inverted
• Object at 2F which is centre of curvature - Image at 2F on the other side.