Rod's Physics 3/4 Questions Thread

[Rod]

Can someone explain the form factor (RMS).

I don't understand what it is or how to calculate it.

Apparently it's the ratio of direct current and alternating current, so what's the significance of this?

Thanks

[lzxnl]

RMS means root-mean-square
It is the square root of the average of the square.
For AC current, which is sinusoidal, it can be shown that the average of a sine function over its period is 1/2. Try it; the function is y = sin(2*pi*f*t) where f is the frequency. Square it and integrate from t = 1 to t = 2. This should be equal to 1/2. Then, square rooting this gives sqrt(2)/2. This is the origin of the sqrt(2)/2 factor in the RMS.
Why do we want this? P = I^2 R. We want average powers, so we want the average of I^2.

Can someone help please? Two questions before and nobody answered . Is everyone busy at uni?

I've just got my head around amplitude modulation and nek minit I see the study design and they want us to know about 'light intensity modulation'. Is that the same thing as amplitude modulation? If not what's the difference? Can someone also post some links thanks

Intensity = amplitude (well they're related, not exactly identical)

An enormous truck is about to hit three stationary carriages. The truck, and each of the three carriages are the same mass. Will the force applied by the truck onto the carriages be higher? Or will the force applied by the stationary carriages be higher?

By calculation, the experience the same impulse. Maybe because of the newton's third law? Not 100% sure.

Thanks

The truck only applies a force to the first carriage. The first carriage then pushes on the truck exactly as hard as how hard the truck pushed on the carriage. Newton 3.

[Rod]

RMS means root-mean-square
It is the square root of the average of the square.
For AC current, which is sinusoidal, it can be shown that the average of a sine function over its period is 1/2. Try it; the function is y = sin(2*pi*f*t) where f is the frequency. Square it and integrate from t = 1 to t = 2. This should be equal to 1/2. Then, square rooting this gives sqrt(2)/2. This is the origin of the sqrt(2)/2 factor in the RMS.
Why do we want this? P = I^2 R. We want average powers, so we want the average of I^2.

Intensity = amplitude (well they're related, not exactly identical)

The truck only applies a force to the first carriage. The first carriage then pushes on the truck exactly as hard as how hard the truck pushed on the carriage. Newton 3.

Thanks so much man

[Rod]

Need some help guys,

So was just doing some questions where you need to sketch the output versus time graph of an amplifier using a transfer characteristic and the input versus time graph. Usually, when you get a clipped output versus time graph, questions tend to go 'how can the input signal be altered so that an efficient output graph is obtained'

So it pretty much means to figure out a way to alter the input versus time graph whereby the output versus time graph of the amplifier is no longer clipped.

At first I had no idea how to do this, but I've got a couple of thoughts.Could someone please clarify/edit my approach:

- I went back to the transfer characteristic and looked at the quotient (middle of the transfer characteristic). Say, it's 2V for input, I shift the input versus time graph up by 2, which gave me a totally new graph. Then I used it to and was actually able to sketch an output vs time graph that is not clipped.

Was this just a fluke? Or is it actually the appropriate way to do these questions?

Thanks so much, a quick reply would be great StevensMay/Lxnl/PB and others

[Stevensmay]

Sorry for the delay Rod. That is pretty much the approach, simply increasing/decreasing your input voltage to move your input signals into a non-clipping region.

[Rod]

Sorry for the delay Rod. That is pretty much the approach, simply increasing/decreasing your input voltage to move your input signals into a non-clipping region.

thanks steven =]

[Rod]

Can someone please give me a consise explanation of 'peak to peak'. And also 'peak'

Diagrams/Examples would be great as well.

My textbook hasn't covered it and I don't really understand it. Isn't 'peak to peak' just the difference between the two maximum peaks? Need help !

[lzxnl]

Think of AC voltage as a sine wave (it actually is a sine function of time). Then, the amplitude is the peak voltage, twice the amplitude, or the distance from the bottom peak to the top peak is peak-to-peak etc

[Rod]

Think of AC voltage as a sine wave (it actually is a sine function of time). Then, the amplitude is the peak voltage, twice the amplitude, or the distance from the bottom peak to the top peak is peak-to-peak etc

Thanks, and how about 'peak'?

[Rod]

So for example; 'the amplifier's linear region can accept signals up to 4mV (peak)'

[lzxnl]

Thanks, and how about 'peak'?

Peak = amplitude

[Rod]

Peak = amplitude

yep i swear I knew that haha

Don't like how they are binding unit 4 stuff into unit 3 stuff tho ;(.

[Rod]

Need some help here;

Just going all the way back to motion, I think I've memorized the graphs. I want to understand them.

Like for example, the area of a vxt graph gives displacement, or the area of a gravitational field verse distance graph gives work.

Why? I want to understand why. Derivatives, antiderivatives?? Can someone pls explain, VCAA could give out a random graph and I want to understand how to interpret what the area + gradient will give

Thanks

[lzxnl]

Need some help here;

Just going all the way back to motion, I think I've memorized the graphs. I want to understand them.

Like for example, the area of a vxt graph gives displacement, or the area of a gravitational field verse distance graph gives work.

Why? I want to understand why. Derivatives, antiderivatives?? Can someone pls explain, VCAA could give out a random graph and I want to understand how to interpret what the area + gradient will give

Thanks

Velocity is the rate of change of position over time, so the change in position is the integral of velocity. Repeat this logic for force against time, acceleration against time etc.

As for force distance graphs, if you split up a force distance graph into many tiny vertical slices, the area of each slice is like the force at that point times the displacement, which is the work done over that small displacement. Sum the slices for the work done from x=a to x=b

[Rod]

With a digram (if you have time), can someone explain what solenoids are? I'm really confused with what we're expected to know