TrueTears question thread

[jules]

when determining the gain of a voltage amplifier, and say its an inverting amplifier, is the gain therefore negative or do we take the magnitude?

[Flaming_Arrow]

take the magnitude

[TrueTears]

Bias of the diode prevents current flow from smoothly alternating (due to switch-on voltage). Hence to preserve the signal, the demodulated signal at Y is the bottom left.

Modulation/demodulation is not a process where the input signal is 'exactly copied' to the output device. Only the frequency and amplitude are preserved.

Ah I see, thanks Mao! So what type of signal would you expect to see at Z? (This is not part of the actual question but I'm just wondering)

[dejan91]

Well since it's going through the amplfier, wouldn't you see it amlpified?

Also, does it really matter if you put in a positive or negative gain? Apparently they accept both. Strictly speaking, if the amplifier is inverting, and you didn't have a graph to work with (just the gain formula, nor did they tell you it was an inverting amplifier) you should be able to plot a Vout graph just as well as if you had the vin graph. If you had the gain as positive, you would get the wrong graph.

[NE2000]

Bias of the diode prevents current flow from smoothly alternating (due to switch-on voltage). Hence to preserve the signal, the demodulated signal at Y is the bottom left.

Modulation/demodulation is not a process where the input signal is 'exactly copied' to the output device. Only the frequency and amplitude are preserved.

Ah I see, thanks Mao! So what type of signal would you expect to see at Z? (This is not part of the actual question but I'm just wondering)

Amp would include decoupling, which will result in it being back to being centred around zero I would imagine. I made that mistake on that question too, but if you think about a photodiode circuit, you can't produce negative voltage when the brightness is low, if the brightness is low then the current through the circuit is zero (or a bit more perhaps) and the voltage out will be around zero as well.

[naved_s9994]

Are questions like (A) relative to (B) still on course?

[Damo17]

Are questions like (A) relative to (B) still on course?

no, relative motion is out.

[naved_s9994]

thnx

[TrueTears]

A stationary electron in a magnetic field experiences no force right? So there is not current hence no magnetic force. But the faster the electron moves the stronger the force [F = Bqv]. So if you were sitting on an electron moving through a magnetic field, what would you observe?

[Mao]

by the right hand rule, the force on the electron is perpendicular to the direction of motion. So the world would be moving past at a certain velocity, and accelerating in a perpendicular direction.

[note, a stationary charge experiences no force because it does not generate any magnetic field. only a moving charge can generate a magnetic field.]

[mark_alec]

So if you were sitting on an electron moving through a magnetic field, what would you observe?

An electric field with the correct direction and magnitude so that the force you experience would be the the same as the force observed from someone who is stationary with respect to the magnetic field.

[TrueTears]

Thanks guys.

Another one:

When current is connected to solenoid containing 2 iron rods side by side the 2 rods move apart, why does this happen?

[Mao]

a magnetic field is induced in the rods, and they are pointing in the same direction, hence repel

[TrueTears]

Thank you!

[methodsboy]

im not up to that stuff..it looks intimidating