Question

Consider Fig.11.1 for photo emission. 

How would you reconcile with momentum-conservation? Note light (photons) have momentum in a different direction than the emitted electrons.

Answer 1

The momentum is transferred to the metal. At the microscopic level, atoms absorb the photon and its momentum is transferred mainly to the nucleus and electrons. The excited electron is emitted. Conservation of momentum needs to be accounted for the momentum transferred to the nucleus and electrons.