Question

2. A 10.00 cm. tall light bulb is placed at a distance of 90.0 cm from a concave

mirror having a focal length of 21 cm Determine the image distance and the image size.

Answer 1

$$\frac 1f=\frac 1o+\frac1i,\\\space\\ \frac 1{21}=\frac 1{90}+\frac1{i},\\\space\\ i=27\text{ cm}.$$

The image size:

$$H_i=-\frac ioh_o=-3\text{ cm (inverted image)}.$$