Q. A photon traveling in the positive x-direction collides with a stationary free electron. The incident photon has a wavelength of 0.0310 nm. Post-collision, the electron moves at an angle 𝛼 below the positive x-axis, and the photon deflects at an angle 𝜃 = 66.3° above the positive x-axis. A) Calculate the angle 𝛼 (in degrees). B) Compute the velocity of the electron (in m/s). Solution: 
             PHYSICAL QUANTITY: SCALAR and VECTOR    A  physical quantity  is a property of a material or system that can  be quantified by  measurement. A physical quantity can be expressed as the combination of a magnitude and a  unit.   Ex: 5 kg in this ‘5’ is magnitude and ‘kg’ is unit.    Physical quantity can be operated in two parts:              (i) Scalar Quantity               (ii) Vector Quantity    Scalars:   •   A physical quantity which has only magnitude.   •  They do not have any direction.     ex: time, mass, speed, distance, volume, energy, work, temperature, electric charge.     Vectors:    •  A vector quantity is defined as the physical quantity that has both, magnitude as well as direction.   ex: displacement, force, torque, momentum, acceleration, velocity, etc.    Representation of Vector:   A vector is represented  as a ...