question_answer

Pragiti's father was riding a scooter on highway and she was sitting behind him. While sitting, she observed that at a place when traffic signal turned red from green, her father still continued riding without noticing the signal change.

Pragiti observed the whole situation and said her father to stop. Her father felt happy on his daughter's intelligence.

Read the above passage and answer the following questions:

(i) Which principle is used in maintaining the traffic signals?

(ii) Write an expression for the speed of the photoelectrons.

(iii) Why Pragiti's father became happy?

What kind of values are expressed by Pragiti?

Answer:

(i) The principle of photoelectric effect is used to maintain the traffic signal.

(ii) The required equation of the speed of photoelectron is

            \[v=\sqrt{\frac{2E}{m}-\frac{2\phi }{m}}\] where,   E = energy of photon, m = mass of the electron and       \[\phi \] = work function for the metal. (iii) Pragiti's father was happy and proud on his daughter's presence of mind, awareness of traffic rules with high visual sensibility.