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Q.13 What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Answer :

If the reflected ray is at the angle of 90 degree. to the incident ray, then the angle of incidence is 45 degree. According to the law of reflection, the angle of incidence and the angle of reflection are equal. Therefore, the angle of incidence and the angle of reflection both are 90/2=45 degree.