The photomultiplier tube (PMT) amplifies light by approximately how many times?

• A. 100
• B. 1000
• C. 10000
• D. 100000

Answer: (B)

A photomultiplier tube turns incoming photons into a detectable electrical signal by first releasing electrons at the photocathode and then multiplying those electrons through a chain of dynodes. Each dynode stage boosts the number of electrons, and with many stages the overall amplification becomes extremely large. In many teaching contexts, a practical rough figure for that overall gain is around 10^3, meaning the output current is about a thousand times larger than the initial photocathode current. The exact gain depends on the PMT design and the voltage applied; some high-sensitivity PMTs can reach much higher gains (up to around 10^6 or more), while lower voltage operation yields smaller gains. So, using 1000 as an approximate amplification captures a common, usable estimate for typical instructional or routine measurements.