Cant remember studying this but if anyone can help me out that that would be sweet

[lofty84]

Hi im reviseing for my 203 and this question has got me stumped its a bit hard to draw it out exactly as tthe lines do not match up but its basically two lines that form a right angle with an arrow head on the end of them.

Its quite hard trying to remember things as if you failed an exam you just moved on as the resists weremonths away. Haveing got through everything else it would be nice to get this one under my belt so its just the 301, 302, and 303 to do but I dont remember looking at things like this.




_ _ _ _ _ _ _ _ _ _ > I ref
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V

V (this is the letter V)

the possible answers are

a. purely resistive
b.purely capacitive
c.resistor and inductor in series
d.purely inductive

the answer is b (purely capacitive) but why is this is the picture supposed to be showing me something

thankyou

 

[Sintra]

Re: Cant remember studying this but if anyone can help me out that that would be swee

ive tried to work this out one out but dont seem able to

a capacitor of capacitive reactance 5 ohms an inductor of 8 ohms inductive reactance and a resistor of 4 ohms are connected in series to a 230v 50 hz supply. the total impedance of the circuit will be

exams in half hour

Z= SqRt(R x R + XL x XL)

Inductive reactance and capacitive reactance cancel each other out so you are left with 3 ohms inductive. Therefore.

Z= SqRt(4 x 4 + 3 x 3)

Z= SqRt(16 + 9)

Z= SqRt(25)

Z= 5 ohms

 

[Adam W]

Re: Cant remember studying this but if anyone can help me out that that would be swee

ive tried to work this out one out but dont seem able to

a capacitor of capacitive reactance 5 ohms an inductor of 8 ohms inductive reactance and a resistor of 4 ohms are connected in series to a 230v 50 hz supply. the total impedance of the circuit will be

exams in half hour

You don't even have to find XL and XC so it's easy:

Z = √R²+(XL~XC)²
Z = √4²+3²
Z = 5Ω

 

[Adam W]

Re: Cant remember studying this but if anyone can help me out that that would be swee

Well same answer as Sintra, just remember:

Formula
Figures in the formula
Answer.

... Not that you'll get anything that dificult in the exam.
Good luck!

 

[lofty84]

Re: Cant remember studying this but if anyone can help me out that that would be swee

Cant beleive it as I got a distinction. Thanks to everybody who helped me you were superb.

 

[JUD]

Re: Cant remember studying this but if anyone can help me out that that would be swee

Maybe if you tell us what you're not getting we could help you.

Here are some of my notes:

Capacitive Reactance Current leads

Xc = 1 ÷ (2 x π x f x C)

f = 1 ÷ (2 x π x C x Xc)

C = 1 ÷ (2 x π x f x Xc)

Xc = Capacitive Reactance (Ω), f = Frequency (Hz), C = Capacitance (F)

----------------------------------------------------------------------------------------------

Inductive Reactance Current lags

XL = 2 x π x f x L

XL = Inductive Reactance (Ω), f = Frequency (Hz), L = Inductance (H)

---------------------------------------------------------------------------------------------

Total Reactance

X = XL ~ Xc

X = Total Reactance (Ω), XL = Inductive Reactance (Ω), Xc = Capacitive Reactance (Ω)

Subtract the lower value out of your Capacitive and Inductive Reactances from the higher value.

In the case of the above question that would be 8 - 5 = 3Ω Inductive Reactance.

------------------------------------------------------------------------------------------

Impedance

Z = √(R² + X²)

R = √(Z² - X²)

X = √(Z² - R²)

Z = Impedance (Ω), R = Resistance (Ω), X = Reactance (Ω)

-----------------------------------------------------------------------------------------

So you now have your values for resistance (R) and reactance (X).

To work out your impedance (Z), the formula is:

Z = √(R² + X²)
Z = √(4² + 3²)
Z = √(16 + 9)
Z = √(25)
Z = 5Ω

 

[w crane]

Re: Cant remember studying this but if anyone can help me out that that would be swee

TRY THESE TWO MEMORY AIDS

1/ "C I V I L" aid.

Capacitance Current leads Capacitance Voltage. and/or lnductance Current lags inductance Voltage

2/
and old Red Indian word: "SOH,CAH,TOA",for phasor dia: ie Sine = Opposite over Hypot
Cosine = Adjacent over Hypot..
Tan =Opposite over Adjcent
see the patten hope it helps.