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

 

[Adam W]

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

heres a weird one

what is the power factor of a circuit with a capacitor connectd in series, given the resistance is 6 ohms and the capacitive reactance is 8 ohms

answers are

0.6 lagging
0.75 leading
0.6 leading
0.75 lagging

completely stumped on this one

pf = R ÷ Z

You have the value for R so you need to find Z first

Z = √(R²+XC²)
Z = √(6²+8²)
Z = 10


pf = R ÷ Z
pf = 6 ÷ 10
pf = 0.6

Remember the word "CIVIL" -
C I V = Capacitive, current (I) leads the voltage (V)
V I L = Inductive (L), current (I) comes after V, therefore lags.

It's a capacitive circuit, so the pf will be 0.6 leading.

 

[pushrod]

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

heres a weird one

what is the power factor of a circuit with a capacitor connectd in series, given the resistance is 6 ohms and the capacitive reactance is 8 ohms

answers are

0.6 lagging
0.75 leading
0.6 leading
0.75 lagging

completely stumped on this one

notice the values 6 ohms and 8 ohms (multiples of 3 and 4) impedance is 10 ohms (multiple of 5)
using pythagorus - if you need it

PF=R/Z
=6/10
= 0.6

and a capacitor means it is leading

edit : apologies novice sparkus didn't see you had answered it on the next page - at least we agree lol

 

[JUD]

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

Im back with another .lets hope it doesnt continue at this rate as I have 140 practice questions.

ok

what is the kva of aload given that the true power is 100kW and the ractive power is 25 kVAr

options are

a. 175 kVA
b. 150 kVA
c. 200 kVA and
d. 125 KVA

the answers d (125 kVA) but surely you dont add the 25 kVAr to the 100 Kw and what with 100 added to 25 being 125 just stick a kVA on the end

I get 103kVA for this one.

kVA = √(kW² + kVAr²) = √(100² + 25²) = 103kVA

 

[pushrod]

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

I get 103kVA for this one.

kVA = √(kW² + kVAr²) = √(100² + 25²) = 103kVA

Aaah the good old option E) !!

In actual fact it is D)



It is the typical trick typo question - the typist mistook a 7 for a 2! The reactive power is actually 75 kVAr!

I know this because for some reason the examiners have a fascination for 3, 4, 5 triangles - in this case 75, 100, 125 - why i don't know - maybe they don't own calculators.

 

[JUD]

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

Aaah the good old option E) !!

In actual fact it is D)



It is the typical trick typo question - the typist mistook a 7 for a 2! The reactive power is actually 75 kVAr!

I know this because for some reason the examiners have a fascination for 3, 4, 5 triangles - in this case 75, 100, 125 - why i don't know - maybe they don't own calculators.

Of course. I should have known.

You have to correct the question before you answer it.

 

[lofty84]

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

if anyone can help me to answer these id be greatfull as my exams in the morning

the power factor of a resistive and capacative circuit haveing an impedance of 3 ohms and a resistance of 2.5 ohms is

the answers 0.83 leading

 

[JUD]

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

if anyone can help me to answer these id be greatfull as my exams in the morning

the power factor of a resistive and capacative circuit haveing an impedance of 3 ohms and a resistance of 2.5 ohms is

the answers 0.83 leading

pf = Resistance ÷ Impedance

2.5 ÷ 3 = 0.83 (leading because it's capacitive)

 

[Sintra]

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

PF=R/Z

PF=2.5/3

PF = 0.83 leading as its capacitive

 

[lofty84]

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

thanks alot guys

 

[lofty84]

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

if anyone knows why the kva of a load is 125 Kva given that the true power is 100kW and the reactive power is 75Kvar that would be handy.

 

[pushrod]

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

if anyone knows why the kva of a load is 125 Kva given that the true power is 100kW and the reactive power is 75Kvar that would be handy.

You should be working these out for yourself now enough people have explained it - have a look back at some of the replies from NovusSparkus, JUD and others. Not wishing to be a pain in the ---, but in your exam you will be there by yourself. This example is very similar to others you have posted.

 

[Phil]

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

if anyone knows why the kva of a load is 125 Kva given that the true power is 100kW and the reactive power is 75Kvar that would be handy.

i will do the exam for 50 quid if you want plus travelling

 

[lofty84]

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

If you was local id take you up on it


A transformer has a primary winding with 1100 turns and 380 secondary turns. It is connected to a 230v supply. What will the secondary voltage be?

 

[JUD]

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

If you was local id take you up on it


A transformer has a primary winding with 1100 turns and 380 secondary turns. It is connected to a 230v supply. What will the secondary voltage be?

380 ÷ 1100 x 230 = 79.5V

or

230 ÷ (1100 ÷ 380) = 79.5V

 

[lofty84]

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

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