Question

When a photomultiplier tube was used, the photo current recorded is 60 μA. The actual photo current is
(A) >60 μA
(B) =60 μA
(C) <60 μA
(D) None of these.

Answer 1

Hint:Photomultiplier tube multiplies the quantity of current. A photomultiplier tube, useful for light detection of very weak signals, is a photoemissive device in which the absorption of a photon results in the emission of an electron.

Complete step by step answer:
A photomultiplier tube consists of a photoelectric cell and a series of electrodes used for the detection of light of very weak signals. It is a photo emissive device in which the absorption of a photon results in the emission of an electron. These detectors work by amplifying the electrons generated by a photocathode exposed to a photon flux (The photon flux is defined as the number of photons per second per unit area). The function of a photomultiplier tube (PMT), are extremely sensitive detectors and they multiply the current produced by incident light by as much as 100 times the actual current. Photomultipliers are used in numerous medical equipment designs. Example - Blood analysis devices. The actual current has to be less than 60 μA as dark current is also involved in the measured current value.
Actual current = measured current – dark current.
Hence, the option C is correct.

Note: The actual current is always less than the current recorded by the photomultiplier because it is used to increase the magnitude of current in various devices. The word photomultiplier is made up of two words photo which means light and multiplier means to multiply something i.e., to increase the value by certain times. So, from the word photomultiplier we can say that it multiplies the current.