How are focal length and radius of curvature connected?

21 Draw the colour circle showing primary and composite colours. 22 What is meant by dispersion of light? 24 An object 5 cm high is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagrams and find the position, size and the nature of the image formed. 25 A concave lens of focal length 15 cm, forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.