7. (a) A radioactive sample contains 530 x 10 g of nobelium-259, which has a half-life of 59 min. i) How many atoms of nobelium-259 are in the sample initially? ii) What is the initial activity of the sample? iii) What is the activity of the sample after 8h? [10] (b) What is meant by total internal reflection of light? State the conditions under which it occurs. Define critical angle and explain how the critical angle for a material in air depends on its refractive index. [5] (c) A ray of light is incident on the face AC of a glass prism, n = 1.51 as shown in Figure 7.1. (Air) n = 1.00 Figure 7.1 A n = 1.51 B i) What is the angle of refraction at the surface AC? ii) What is the angle of incidence on the surface BC