hello,

Im student, Im reading the book "the art of electronics - horowitz hill", There is a part of the book wich it has "bad circuits", i would like to know whats the problem in that circuits(check pictures),
whats wrong and why in each circuit?

Thanks to all!

 

In both figures, the wrong kind of transistor is used: in pic1 the transistor should be a PNP, not an NPN; and in pic2 the transistor should be an NPN, not a PNP.

 

The normal current flow through a transistor is in the direction of the emitter arrow.
That's how you determine which polarity transistor to use in a circuit.

 

The polarity of voltage is applied in the reverse of what is required for the type of transistor shown.

 

very thanks to all

 

The normal current flow through a transistor is in the direction of the emitter arrow.

I don't know if you were taught this or not yet,
When you see the phrase above, it is referring to conventional current flow, (positive current), it is not referring to electron current flow, as have been taught about a flashlight circuit.

 

The normal current flow through a transistor is in the direction of the emitter arrow.

Bipolar transistor. Mosfets have it for some reason the other way around.

 

With a reverse bias of 15 V, it is possible that the pic2 transistor will conduct.

ak