Q. The average threshold of dark-adapted (scotopic) vision is 4.00x 10-11 W/m2 at a central wavelength of 500nm. If light having this intensity and wavelength enters eye and pupil is open to its highest diameter of 6.5mm, how various photons per second enter the eye?
Q. Quarks carry spin 1/2. Three quarks bind together to make a baryon (such as the proton or neutron); two quarks (or more precisely a quark and an anti-quark) bind together to make a meson (for example the pion or the kaon). Suppose the quarks are in the ground state (so the orbital angular momentum is zero)