Question

Which of the following is a use of photocell?

• A. Detection of traffic signal violators.
• B. For giving theft warnings in banks, treasuries etc.
• C. Helps in counting the persons entering an audition.
• D. All of the above

Answer 1

The correct option is D All of the above

In case of first three options, photocell is used. As any object/person blocks the light incident on the cathode of the photocell, the photoelectric current becomes zero. This principle is used in detection of persons/objects.

Hence, $\left(D\right)$ is the correct answer.