An object 4cm high is placed at a distance of 10cm from a convex lens of focal length 20cm. Find the position, nature and size of the image.

The two rays chosen for the construction of ray diagram is:

Ray 1: When the incident ray is parallel to the principal axis, the reflected ray will pass through the focus of concave mirror or it appears to pass through the focus of convex mirror.
Ray 2: When the incident ray passes through or appears to pass through the centre of curvature, the light, after reflection from the spherical mirror, reflects back along the same path.
The image formed is real, inverted, magnified and is formed beyond the centre of curvature.

Draw the following diagram, in which a ray of light is incident on a concave/convex mirror, on your answer sheet. Show the path of this ray, after reflection, in each case.

The magnification of an image formed by a lens is –1. If the distance between the object and its image is 60cm, what is the distance of the object from the optical centre of the lens? Find the nature and focal length of the lens. If the object is displaced 20cm towards the optical centre of the lens, where would the image be formed and what would be its nature? Draw a ray diagram to justify your answer.

A convex lens of focal length 0.10m is used to form a magnified image of an object of height 5mm placed at a distance of 0.08m from the lens. Calculate the position, nature and size of the image.

The image of an object formed by a lens is of magnification - 1. If the distance between the object and its image is 60 cm, what is the focal length of the lens? If the object is moved 20 cm towards the lens, where would the image be formed? State reason and also draw a ray diagram in support of your answer.

For which position of the object does a convex lens form a virtual and erect image? Explain with the help of a ray diagram.

How are power and focal length of a lens related? You are provided with two lenses of focal length 20cm and 40cm respectively. Which lens will you use to obtain more convergent light?

Giving reasons, state the ‘signs’ (positive or negative) which can be given to the following:

1. Object distance (u) for a concave mirror or convex mirror.
2. Image distances (v) for a concave mirror.
3. Image distances (v) for a convex mirror.

How far should an object be placed from a convex lens of focal length 20 cm to obtain its image at a distance of 30 cm from the lens? What will be the height of the image if the object is 6 cm tall?