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I have designed a circuit (from a book) which uses BC547 transistor(npn) ,220 ohm resistor ,LED, battery. The circuit is as shown in the image I have uploaded. Now if I touch the base of transistor and the anode(+ve one) of led with my fingers, the led glows. Can anyone please elaborate me what's actually happening in the circuit ,how the current flows in the circuit and also how the transistor works in this circuit. enter image description here the collector is connected to the resistor.

aditya
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    Your fingers are acting like a high-value resistor to send a small current into the base of the transistor. – Hearth May 11 '18 at 16:37
  • can you please elaborate how the current flows in the whole circuit and also how the transistor works here – aditya May 11 '18 at 16:40
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    Books have been written about how transistors work. There are also many internet sites about the theory. Have you been to research this anywhere? If so, what is it that you didn't understand? This site has pretty good answers if you care to use the search bar but adding another "how transistors work" Q&A seems rather a waste of time. Go googling/searching. Try googling "common emitter amplifier". – Andy aka May 11 '18 at 16:42
  • Possible duplicate of [Basics of Transistors](https://electronics.stackexchange.com/questions/15975/basics-of-transistors) – Ariser May 11 '18 at 17:12
  • My doubt is does the battery gets discharged even though the led does not glow. – aditya May 11 '18 at 17:12
  • @aditya Those doubts can be resolved by measuring the current. – Dmitry Grigoryev May 14 '18 at 08:35

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What you have is this:

schematic

simulate this circuit – Schematic created using CircuitLab

The resistor R2 is your hand. A small amount of current is able to flow through your hand into the base of the transistor, turning it on. The BC546 can have a very high hFE (up to 800 according to the datasheet), so this small current into the base is enough to produce a current of a few mA into the collector, lighting the LED.

Hearth
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