True or False: With normal incidence, the angle is 180 degrees.

True or False: With normal incidence, the angle is 180 degrees.

• A. True
• B. False
• C. Not defined
• D. It depends

Answer: (B)

The main idea is how we define the angle in incidence and reflection. The angle of incidence is measured between the incoming beam and the normal to the surface. When incidence is normal, the beam hits straight on, so it is perpendicular to the surface and the angle relative to the normal is 0 degrees. The reflected beam leaves along the same line but in the opposite direction, so the angle between the incident and reflected beams is 180 degrees, but that 180-degree relationship is not the angle of incidence. Therefore the statement is false when referring to the incidence angle.

The main idea is how we define the angle in incidence and reflection. The angle of incidence is measured between the incoming beam and the normal to the surface. When incidence is normal, the beam hits straight on, so it is perpendicular to the surface and the angle relative to the normal is 0 degrees. The reflected beam leaves along the same line but in the opposite direction, so the angle between the incident and reflected beams is 180 degrees, but that 180-degree relationship is not the angle of incidence. Therefore the statement is false when referring to the incidence angle.