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Table 13.1 :Angles of Incidence A ray of light is an idealisation. In and Reflection reality, we have a narrow beam of light which is made up of several S. Angle of Angle of rays. For simplicity, we use the term ray for a narrow beam of light. No. Incidence (∠ i) Reflection ( ∠r) 1. Draw lines showing the position of 2. the plane mirror, the incident ray and the reflected ray on the paper with the 3. help of your friends. Remove the mirror 4. and the comb. Draw a line making an 5. angle of 90º to the line representing the mirror at the point where the incident Do you see any relation between the ray strikes the mirror. This line is known angle of incidence and the angle of as the nor mal to the reflecting surface reflection. Are they approximately equal? at that point (Fig. 13.2). The angle If the experiment is carried out carefully, it is seen that the angle of incidence is always equal to the angle of reflection. This is one of the laws of reflection . Let us perform another activity on reflection. Fig. 13.2 : Drawing the normal What would happen if I between the normal and incident ray is called the angle of incidence ( i). The threw the light on the ∠ mirror along the normal. angle between the normal and the reflected ray is known as the angle of Activity 13.2 reflection (∠ r) (Fig. 13.3). Measure the angle of incidence and the angle of Perform Activity 13.1 again. This reflection. Repeat the activity several time use a sheet of stiff paper or a times by changing the angle of chart paper. Let the sheet project a incidence. Enter the data in Table 13.1. little beyond the edge of the Table (Fig. 13.4). Cut the projecting portion of the sheet in the middle. Look at the reflected ray. Make sure Reflected Incident that the reflected ray extends to the ray ray projected portion of the paper. Bend Normal that part of the projected portion on which the reflected ray falls. Can you still see the reflected ray? Bring Fig. 13.3 : Angle of incidence and angle of reflection the paper back to the original 166 SCIENCE 2024-25