A candle is kept at a distance of 90 cm from the curtain. Where to place a 20 cm focus-distance convex lens?

A point object is placed at a distance of 15 cm from a convex lens. The image is formed on the other side at a distance of 30 cm from the lens. When a concave lens is placed in contact with the convex lens, the image shifts away further by 30 cm. Calculate the focal lengths of the two lenses.

A convex lens is coaxially placed with a concave lens. A screen is placed at a distance of 100 cm apart from the combination. The focal length of convex lens is 15 cm. Determine the focal length of the concave lens if image of object placed at a distance of 20 cm, from the combination, is projected on the scrcen.

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to size of the object ? Also, find the power of the lens.

An object is placed at a distance of 30 cm from a convex lens of focal length 20 cm.

Ray coming from an object situated at infinity, fall on a convex lens and an image is formed at a distance of 16 cm from the lens. When a concave lens is kept in contact with the convex lens, the image is formed at a distance of 20 cm from the lens combination. Calculate the focal length of the concave lens.

A point object is placed at a distance of 15 cm from a convex lens. The image is formed on the other side of lens at a distance 30 cm from lens. When a concave lens is placed in contact with convex lens, image is shifted away further by 30 cm. calculate the focal lengths of the two lenses.