Radiation of energy \(E\) falls normally on a perfectly reflecting surface. The momentum transferred to the surface is:
(\(c\) = velocity of light)
1. \(E \over c\)
2. \(2E \over c\)
3. \(2E \over c^2\) 
4. \(E \over c^2\)

A \(200~\text{W}\) sodium street lamp emits yellow light of wavelength \(0.6~\mu\text{m}\)$$. Assuming it to be \(25\%\) efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is:
1. \(1.5\times 10^{20}\)
2. \(6\times 10^{18}\)
3. \(62\times 10^{20}\)
4. \(3\times 10^{19}\)