Question

An image Y is formed of a point object x by a lens whose optic axis is AB as shown in Fig. Draw a ray diagram to locate the lens and its focus. If the image Y of object X is formed by a concave mirror (having the same optic axis AB) instead of lens, draw another ray diagram to locate the mirror and its focus. Write down the steps of construction of the ray diagrams

Answer 1

$1^{st}$ Construction

1. Join the line XY which intersects the line AB at O.

2. A line POQ passing through O and $\perp$ to AB will represent the position of the lens.

3. Draw the line from X parallel to AB.Join P to Y, this line intersects AB at F.

OF - focal length of lens.

$2^{nd}$ Construction

1. Draw a line Y'BY $\perp$ to AB. Take BY = BY'.

2. Join XY' and extend it to O. O is the pole of mirror.

3. Join XY which intersects AB at 2F.

4. Take 2F as centre and O to 2F as radius draw an arc MOM'. This represents the position of mirror.

5. Draw XC parallel to AB. Join CY- Intersects at AB at F, which is the focus of mirror.