5. Use graphic method to study reflection, refraction & total internal reflection at plane interface (a) Draw a rectangle on a sheet of white paper to represent a plastic block with side sizes of 9.0 cm and 11 cm respectively as shown in Fig. 13. (b) Draw a surface normal through the middle point of the top surface of the plastic block in your Fig. 13. (c) Draw an incident ray at the top surface of the plastic block with an angle of 20 between the ray and the top surface of the plastic block in your Fig. 13. (d) The critical angle is 390 at the interface from plastic to air. (e) Draw a reflection ray and refraction ray at point P. Extend the refraction ray until it reaches the right-side plastic/air interface of the plastic block. (f) Draw surface normal, reflection ray and refraction ray at the incident point on each of the 3 plastic/air interfaces (right, bottom, left) in your Fig. 13. (g) All the angles of refraction and reflection should be drawn to scale using a protractor, and label them in your Fig. 13. Air Air 20 Plastic block 11 cm V 9.0 cm Figure 13 Rectangle plastic block