CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 24(b)

Any four of the following: (i) Keep the prism exactly within its traced boundary throughout the experiment; do not move it. (ii) Fix the pins vertically, and look at the feet of the pins (not their heads) while aligning them. (iii) Keep the angle of incidence between $30^{\circ }$ and $60^{\circ }$. (iv) Keep the two pins on each side at least 5 cm apart. (v) Use the protractor correctly, measuring the angles from the normal, and draw thin lines with a sharp pencil. (Any other correct precaution also earns credit.)