TrueTears question thread

[TrueTears]

Just a bit stuck on part 2, any help would be appreciated



1. When the student measures the input and output voltages of a simple amplifier on a two-channel oscilloscope, the graphs(above) are displayed. The peak - to - peak voltage of the output is 2V. What is the voltage gain of the amplifier, based on the information given? (indicate in your answer whether the amplifier is inverting or non-inverting.)



so



so

so gain is and it is inverting because it is negative.

2. What are the DC and AC(peak) components of the input voltage?

Erm, I don't really get what this question is asking... 'components' ? 'AC (peak)' ? peak to peak or just the peak?

Thanks in advance

[TrueTears]

A linear inverting amplifier has a gain in its linear region of . Its linear region is from -12 mV through to +12 mV (DC). Outside this region it is non-linear.

Sketch the graph of DC input voltage against DC output voltage for this amplifier between . Label the axes carefully.

If anyone could do a rough sketch on paint or something and explain how they did it, that would be very much appreciated

[dejan91]

I think?

[dejan91]

Vin will remain in the linear region so no clipping will occur, and the graph will be linear. Since the gain is +120, Vout = Vin * gain = 1200mV = 1.2V and -1.2V (for the other peak). Axes must be labelled accordingly with mV and V.

[TrueTears]

Thanks for your help dejan, but the answers say the graph looks like this:



But I don't get why.

[dejan91]

Ahh crap I didn't read your question properly lmao.

Inverting amlpifier, so basically exactly what I did except negative gradient.

[TrueTears]

Yeap, but why is it 1.5 and -1.5 on the axis?

[dejan91]

But looking at your graph.......... -1.5 to 1.5 Voltage output?? Hmmm, that's gotta be wrong considering input voltage is -10 to 10 and gain is -120 not 150.


I don't see any reason why it should be 1.5. I'm gonna going for the old 'the book is wrong' thing, unless you maybe obtained or read a wrong gain.

[TrueTears]

Exactly, which is why I was confused when looking at the answers. haha

[TrueTears]

Answered on MSN Q 1.

thanks Mao

[TrueTears]

The sketch shows an electro-optical system that allows sound to be transmitted over a distance via a fibre-optical cable, using light.

Explain what is happening at each device

Can anyone check if what I said is correct and if I missed anything please point it out

The input analog signal(sound) from the microphone is amplified at the first amp which acts as a transducer and converts the sound analog signal into an electric signal. At the LED, the electrical signal is converted into optical signal by the LED, ie modulation occurs. The light from the LED then acts as the carrier wave which contains all the information from the original analog signal. This optical signal then travels through the optical-fibre wire where it reaches the photodiode at Q. At Q, the optical signal is converted back into an electrical signal, ie demodulation occurs. It is then amplified in the amplifier and then exits through the loudspeaker as sound

[Mao]

1. microphone is the transducer, it transforms sound waves to electric signals
2. amplifier amplifies the electric signal from the microphone (very small)
3. amplified signal is transmitted by electro-optic transducer (LED)
4. optic signal is received by opto-electric transducer (photodiode)
5. signal from the opto-electric transducer is amplified
6. amplified signal is transformed from electric wave to sound waves via loudspeakers

[TrueTears]

Thanks Mao!

[TrueTears]

Oh and also for the modulation that takes place at the LED does it happen like this?

You alter the amplitude of the carrier wave, in this case the light from the LED, to match that of the electrical signal being fed into the LED. So then the LED can 'carry' the electric signal and transfer it through the optical fibre to the photodiode.

And for the demodulation does it happen like this?

At the photodiode the light, which is acting as the carrier wave, is removed and all we are left is the electric signal which is then amplified in the amplifier etc etc.

Thanks again!

EDIT: Oh and also are capacitors in the unit 3 course for physics?

[kurrymuncher]

Oh and also for the modulation that takes place at the LED does it happen like this?

You alter the amplitude of the carrier wave, in this case the light from the LED, to match that of the electrical signal being fed into the LED. So then the LED can 'carry' the electric signal and transfer it through the optical fibre to the photodiode.

yeah, thats how it works.


The modulated signal will be sent along the optical fibre cable. At the end, the modulated signal is detected by a photodiode or photoresistor. The photodiode or photoresistor converts the light back into a fluctuating current in the circuit and so on....

I dont think there are capacitors in unit 3. not sure though