A surgeon is attempting to correct a detached retina by using a pulsed laser. (a) If the pulses last for $20.0 \mathrm{~ms}$ and if the output power of the laser is $0.500 \mathrm{~W}$, how much energy is in each pulse? (b) If the wavelength of the laser light is $643 \mathrm{~nm}$, how many photons are present in each pulse?