Common Emitter Gain Basics (10-Transistors) 

Good catch! Actually, more like about 8.6% of the current (from the voltage divider). Still small enough not to get too worried about.

Im also from india, and I watch these lectures everyday.

Also from India... Are you an engineer?? Or a hobbyist??

I think you're right. Resistance in parallel is always less than all of its component resistances.

You're right.

If I may.. gain is a ratio of the output voltage over the input voltage. So it is unit-less.

@@rolfw2336 interesting. But what does the "gain" in db tell me with eg commercial amplifiers? So how can I derive it?

If the base voltage is fixed to some Vb but the emitter is grounded, then there will be a nonlinear relationship between Ie and Vbe like that of a forward-biased diode. This can lead to it being a little unpredictable - the transistor might be in cutoff with Ie=0 (if Vbe is too low) or with Ie zooming up to some high transistor-burning number if Vbe is a little too high.

@@adannerThanks for the answer!! So it means that I must have a resistor there always? I have seen many (practical) circuits with a common emiter amplifier without a resistor at the emiter. Does it mean that it was wrong? My confusion is based on the problem I see when I try to understand some practical circuits (for example for radio control models, especially old ones from various books but not only) and I compare those circuits with theoretical circuits like here and it doesn't match sometimes. I feel like I am missing something here 🤔

@@grzesiek1x There could be a few reasons. For radio circuits they sometimes use Class C amplifiers for added efficiency (transistor is cutoff for part of each signal cycle) as the added distortion can be managed with a tuned load. The "gain" is a bit tricky though because the output signal then looks different than the input. The amplifier examples in this video are Class A (transistor on and burning power even when there is no signal) so in that sense they are linear.