power dissipated

[J.C.E]

Basically I have got my 301 unit 1 exam next week, and there is this question bugging me in one of these practice mock exams.

Please help, but using the formulas and letters used in the 2330 c+g so I remember it for the exam.

Qst: A capacitor of 100uf is connected in parallel with a 20ohm pure resistor. The group is connected to a 200v 50hz supply. Calculate the power dissipated in the combination.

a.2000w
b.2400w
c.3000w
d3600w

and my teacher said the answer is A. 2000w

What I thought you do:

xc = 1/ 2π x 50 x 0.0001= 31.8ohms

Then add the 31.8ohm reactances to the 20ohm resistor (in parrellel) ....
1/ 31.8 + 1/ 20 = 12.28ohms

Now I have the resistance and the voltage is given so I = V/R =16.29a

and to answer the question, P= V x I (200 x 16.29= 3258watts)

I really can't think of where I am going wrong, I think it something with the way I am add the reactance and resistance together :s

 

[bonio78]

hi, i struggled with this one too, tutor told me that there is no power in capacitor/inductor, (maybe someone with a bit more knowledge could explain why),
the answer is a 2000w

I=v/r= 200/20 =10a
p=IxV = 10x200 = 2000w

hope this helps

 

[J.C.E]

hi, i struggled with this one too, tutor told me that there is no power in capacitor/inductor, (maybe someone with a bit more knowledge could explain why),
the answer is a 2000w

I=v/r= 200/20 =10a
p=IxV = 10x200 = 2000w

hope this helps

I f'ing knew that cap/iduc use 0watts too! (Just forget on this question )

So yes, I think you just do what I did, but don't add the reactance with the resistance and just use the 20ohms

cheers pal

 

[bonio78]

it catches me out sometimes with how the Qs are worded, had my 301 exam last thursday, passed , a lot of Qs on motors in the exam
all the best for next week

 

[J.C.E]

it catches me out sometimes with how the Qs are worded, had my 301 exam last thursday, passed , a lot of Qs on motors in the exam
all the best for next week

motors is probs my weakest area. All the formulas I seem to remember. But with the motors there seems to be loads: ac,dc,3phase...then loads of different ones within these 3! and remembering how to reverse the rotation or what components each has! nighmare mate. But well done on your 301

 

[bonio78]

Cheers, You might be using this site already, www.swindon-massive.co.uk
helped me with revising

 

[J.C.E]

Cheers, You might be using this site already, Web hosting, domain name registration and web services by 1&1 Internet
helped me with revising

yes mate, but cheers anyway

 

[mechelec]

power is only dissipated in the resistor not in capacitors or inductors.

 

[J.C.E]

yup know this, problem solved