The max allowed collector current of a 2N3055 power transistor is 15A. The max allowed base current is 7A. The gain is not 15/7 because the DC current gain is shown to be a minimum of 5 and typically 13 at only 10A and nothing is spec'd above 10A because then its performance is very poor.
The gain is different for each transistor, even if they have the same part number. Some have high gain and some have low gain as shown in the datasheet.
Why do you want to drive a transistor so close to its absolute max rating where it might fail soon.
Why do you want to use a transistor at such a high current and dissipation that it melts?
Why do you want to use a transistor at such a high current that its current gain is almost nothing?
If you want to know the gain of one transistor then measure it.
Ask your teacher.
A high input impedance on an amplifier does not load down the signal source. Most modern audio amplifiers have an input impedance of 10k ohms or more. An opamp can drive a load of 2k ohms or more. If an opamp is loaded with an amplifier that has an input impedance of 10k ohms or more then only a small amount of signal is lost.
The pickup of an electric guitar sounds "normal" when it is loaded with an amplifier with an input impedance of at least 1M ohms.
The input impedance of my oscilloscope is 1M and can be switched to 10M.
The input impedance of my digital multi-meter is 20M.
OK, I have asked many people by they were talking about loading effect, but i think that when there is very low input current or voltage(signal) the ckt.(component) starts conducting. this is the advantages of high input impedance.
This is my question, pls clear the doubt.!!
Some signal sources work best and have the highest output voltage when they are loaded with a high impedance. For example, the pickup for an electric guitar needs to feed an amplifier with an input impedance of 1Meg ohms or more.
The output impedance of a modern solid state amplifier is 0.04 ohms or less. The amplifier will have a rating called "damping factor". When its damping factor rating is 200 and the speaker is 8 ohms then the output impedance of the amplifier is 8/200= 0.04 ohms.
The impedance is so low that it is difficult to measure and almost nobody measures it. The high open-loop gain and high amount of negative feedback in the amplifier produce the very low output impedance. The very low output impedance damps the resonances of speakers.
I have seen video in you tube, he was saying according to your amplifier the speaker resistance should be used for maximum power transfer.
for this resistance of speaker can directly measure through multimeter but how to know about amplifier output resistance ??