Draw ray diagrams to show image formation.
Object at C – concave mirror
Object beyond 2f – convex lens
Object at infinity – concave lens. Write the nature of the image in each case.

26 An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. 27 What is the angle of incidence when the ray reflected back, when it passes from denser to rarer medium. 29 Light, of wavelength of 500 nm in air, enters a glass plate of refractive index 1.5. 
Find   
(i) speed    
(ii) frequency and     
(iii) wavelength of light in glass. 
Assume that the frequency of light remains the same in both media.? 30 Why do we use blue colour solution after washing the clothes?