What is meant by dispersion of light?

20 What is critical angle? Draw a ray diagram showing light incident at the critical angle. 21 Draw the colour circle showing primary and composite colours. 23 How are focal length and radius of curvature connected? 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.