Hiya guys

Can anyone help me with a question I have to do, and I cant

Question is:

A circuit consits of a 10mH inductor in series with a 25 ohn resistor. The Supply to the circuit is 10volts @ 400hz.

Caluclate the:

Reactance of the inductor (Found the formula for this now!)
Imperdance of the circuit
Phase angle between current and voltage
Total Current
Voltage accross Resistor and also Inductor

And I then have to draw a Voltage and imperdance phasor diagram.

Fook.......Anyone able to help?

 

Fuck, now you are taking me back

1) 2 pie f L

2) I *think* you can just add a resistor to give impedance? (as a resistor doesn't change with freq.)

Others - far too long ago...

 

Cheers Steve....... *getting there* . I really should keep better notes!

 

edited above to say about resistor...

Google the rest mate - bound to be able to find something

 

Hmm, in a Resistive circuit, current and voltage are in phase. In an inductive circuit, current lags volatge by 90deg.

Cant find owt about in a circuit with both an inductor and a resistor though . At a guess i'd just be 90deg?

EDIT...no it aint, arse, more equations

 

ignore me

 

Reactance X = 25.1


Impedence is the square root of Resistance squared + Reactance Squared

Z=35.4

Current lags inductor voltage by 90 degrees.


Phase angle : inverse tan of (X/R) = 45 degrees

 

Voltage = Current x Impedence.

So current in circuit is 10V/35.1 = 0.28A

 

Steve, Rick, cheers lads, much appreciated!

Rick, with the phase angle, X = Reactance? and R = Resistance?

So Inverse tan of Reacance/Resistance? = 45deg

Cheers

 

yes. Obvious thats it's gonna be 45 degrees though, as reactance and resistance are equal. Careful when calculating the voltages accross each component - as they, unlike the current are not in phase!

 

Cheers Rick....think ive cracked it.

With the resistor i can work out the V using Ohms Law (as they are in phase). In this case 7v.

Leaveing 10v (supply) - 7v = 3v drop accross the inductor (saves me understanding how to calculate it knowing they are out of phase by 45deg!)

 

You're doing this in a difficult way in my opinion. Just treat every component as a resistor with a complex value and then you can calculate everything with only the Ohm's law. In anycase, good that it got cleared.

 

Jesse (or anyone...) Fancy another question ?

If a 24v battery has an internal resistance of 0.005ohms, and is connected to a resistive load of 1250watts.....

Calculate the total current and circuit voltage!

Im stook...again

You cant work out the terminal voltage as you dont know the current

You cant work out the current from the power as you dont know the terminal voltage

 

I fooking hate analog electronics

 

Solve the current from the second order equation:

R*I^2 - 24V * I + P = 0

Current: 52.661 A
Voltage: 23,737 V

 

Jesse, Any chance you can write the equation/working you used to come to those answers?

 

Uups.. You were fast. I already edited the message to put it there.

 

Fast no.....desperate yes

PS. Any chance you can run it through for the voltage and current again if the batteries internal resistance is now 0.01ohm this time?

Many thanks mate, you are a star

 

I agree it's easier to work with complex values, but it doent give a fundemental understanding as to what is happeneing.

Phase is quite simple Phil. First of, an inductor behaves just like a shock absorber - it doesn't like change, it resists change. If it's got a certain current running through it, and u change the voltage accross it, it tries to oppose the change.

Phase is a kind of way of measuriing the time delay between the current and voltage reaching there peak value.

 

Work out the phasor diagram first, then the phase will be just a geometrical angle.

 

You know what i find most impressive in this topic?







The fact Jesse can discuss a very complex subject like this in OUR native language

 

Ive thought that many times Stu, how loads of PF users, and even a few lads on my course from Mayalsia etc can not only just about speak englisah, they speak it and understand it well enough to be tought in English, thats impressive!

If i went to say France, I could just about get by (GCSE french lol), but could i sit in a french uni and learn? hell no.

Big respect to people who can do that!

 

I teach this shit in the University in english

 

Absolutely fooking quality turnup for the thread

 

Takes me back to uni

I read the question and started thinking "come on, you can remember this!"

Then Jesse and Rick kicked the arse clean out of it

Neil.

 

same here!!

and I graduated in 2004!!

 

Passionford wins again