Required practical on refraction?

1)Set up a ray box, slit and lens so that a narrow ray of light is produced. 2)Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’. 3)Place the longest side of a rectangular acrylic polymer block against the first line. With the normal near the middle of the block, carefully draw around the block without moving it. 4)Use the ray box to shine a ray of light at the point where the normal meets the block. This is the incident ray. 5)The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the block and another clear ray leaving the opposite face of the block. 6)Using a pencil on the paper, mark the path of: the incident ray with a cross the reflected ray with a cross the ray that leaves the block with two crosses - one near the block and the other further away 7)Remove the block. Join the crosses to show the paths of the light rays. 8)Repeat steps 2 to 7 for a rectangular glass block. 9)Measure the angle of incidence, angle of refraction and angle of reflection for each block.