(1) The speed of light in a material is 0.50 c. What is the critical angle of a light ray at the interface between the material and a vacuum?
(2) The intensity of sunlight impinging on the Earth is about 1.4 kW/m2. What is the power emitted by the Sun in the spectrum of frequencies? (Earth-Sun distance =1.5*10^8 km, Earth radius=6.4*10^3 km)