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
|_|
|
|
|
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

 

[ian.settle1]

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

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
|_|
|
|
|
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

It is showing you that the current leads the voltage by 90 degrees as a pure cpactive circuit

 

[lofty84]

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

Heres another that I cant remember howto do

A transformer takes aload of 25 KVAat a power factor of 0.8.calculate the input power in KW

a.31.25 KW
b.200 KW
c.20 KW
d.312.5KW

The answers c. 20 KW

Ive worked out that 0.8 x 25 is 20 but how come you do it this way instead of say doing 25000/0.8

 

[lofty84]

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

I cant beleive this lol ten questions in and heres the third one im stuck with.

if a 8 kw motorwith a power factor of 0.9isconnected across a 400v supply, calculate the current taken by the load ?

a.20 A
b.22.2 A
c.2.88 MA
d.2.22 A

the answers 22.2A and I guessed right but I wouldnt mind knowing how to do the calculation

 

[lofty84]

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

This isnt looking good but at least ive given myself a chance by starting the revision early

How many numbers of turns are needed on a transformer if the primary windings are 1000 and the primary and secondary currents are 5 A and 20 A respectivly.

the options are

a. 200 turns
b.250 turns
c.100 turns
d. 50 turns

the answers b and i did come to that conclusion but was the way i did it right.

I said 1000/5 = 200

and 1000/20= 50

I then addedthem together

 

[ian.settle1]

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

Heres another that I cant remember howto do

A transformer takes aload of 25 KVAat a power factor of 0.8.calculate the input power in KW

a.31.25 KW
b.200 KW
c.20 KW
d.312.5KW

The answers c. 20 KW

Ive worked out that 0.8 x 25 is 20 but how come you do it this way instead of say doing 25000/0.8

How do you get the input lower than the output think you will find the answer is A

 

[lofty84]

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

 

[lofty84]

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

another

what is the total impedance of a circuit with a 4 (ohms sign) resistor and a 10 mH inductor

no idea on how to work this one out

4 (ohms)
7 (ohms)
5 (ohms)
6 (ohms)


the answers 5 ohms but ive no idea how to work that out

 

[lofty84]

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

How do you get the input lower than the output think you will find the answer is A

It deffinantly said the answer was C mate just went back and double checked. Do you think thats wrong then Ian. Thanksfor haveng a look for me

 

[Adam W]

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

This isnt looking good but at least ive given myself a chance by starting the revision early

How many numbers of turns are needed on a transformer if the primary windings are 1000 and the primary and secondary currents are 5 A and 20 A respectivly.

the options are

a. 200 turns
b.250 turns
c.100 turns
d. 50 turns

the answers b and i did come to that conclusion but was the way i did it right.

I said 1000/5 = 200

and 1000/20= 50

I then addedthem together

I don't know why your way works or even if it does or if it's just a coincidence, but:

Power in = Power out
Therefore the voltage must be inversely proportional to the current, ie the higher the current the lower the voltage to produce the same power, and vice versa.

First find the ratio:
20/5 = 4

Then apply the ratio of power and/or voltage to the number of turns:
1000/4 = 250


I appear to have mislaid the [divided by] button on my keyboard; I'm sure it used to have one.

 

[Adam W]

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

another

what is the total impedance of a circuit with a 4 (ohms sign) resistor and a 10 mH inductor

no idea on how to work this one out

4 (ohms)
7 (ohms)
5 (ohms)
6 (ohms)


the answers 5 ohms but ive no idea how to work that out

With almost all the reactance questions they throw at you you'll have to find XL or XC.
Assuming f (frequency) = 50 HZ

XL = 2[Pi] f L
XL = 2x[Pi]x50x0.01
ZL = 3.14

Now you have the reactance of the coil you can find the total impedance:


Z = [square root] (R[squared] + XL~XC[squared])
Z = [square root] (4[squared] + 3.14[squared])
Z = [square root] 16 + 9.87
Z = 5

Could do with being able to use scientific symbols here...

 

[lofty84]

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

hopeing for a question like that now, nicely explained and very much appreciated

know any of the others

 

[amer]

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

if i am not mistaken the formula is and the answer is 250 [FONT=&quot]Np Is transpose formula [/FONT]
[FONT=&quot]─ ─ Ns= Np×Ip[/FONT]
[FONT=&quot]Ns Ip ─────[/FONT]
[FONT=&quot] Is[/FONT]

 

[amer]

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

if i am not mistaken the formula is and the answer is 250 [FONT=&quot]Np Is transpose formula [/FONT]
[FONT=&quot]─ ─ Ns= Np×Ip[/FONT]
[FONT=&quot]Ns Ip ─────[/FONT]
[FONT=&quot] Is[/FONT]

 

[Guest123]

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

I cant beleive this lol ten questions in and heres the third one im stuck with.

if a 8 kw motorwith a power factor of 0.9isconnected across a 400v supply, calculate the current taken by the load ?

a.20 A
b.22.2 A
c.2.88 MA
d.2.22 A

the answers 22.2A and I guessed right but I wouldnt mind knowing how to do the calculation

I get 12.8A....

 

[Guest123]

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

Heres another that I cant remember howto do

A transformer takes aload of 25 KVAat a power factor of 0.8.calculate the input power in KW

a.31.25 KW
b.200 KW
c.20 KW
d.312.5KW

The answers c. 20 KW

Ive worked out that 0.8 x 25 is 20 but how come you do it this way instead of say doing 25000/0.8

KW - KVAxPF = 25x0.8 = 20.

 

[Adam W]

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

I cant beleive this lol ten questions in and heres the third one im stuck with.

if a 8 kw motorwith a power factor of 0.9isconnected across a 400v supply, calculate the current taken by the load ?

a.20 A
b.22.2 A
c.2.88 MA
d.2.22 A

the answers 22.2A and I guessed right but I wouldnt mind knowing how to do the calculation

I had to get my notes out for these - reactance I can do, but I struggled with this.

P
I = --------
V x pf



8000
I = -------------
400 x 0.9



I = 22.2A​

 

[Guest123]

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

What about root 3 (1.732) ???

 

[Adam W]

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

That would give an answer of 38.5A, which wasn't one of the options.
I seem to remember 3 phase supplies have to be treated differently but the question just stated it was a 400v supply with no mention of 3 phase, so I didn't want to over-complicate the issue.

 

[lofty84]

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

Thanks to everyone whos tried to help me. Really is much appreciated.

in regards to the sq root of three the 1.732 does that only comeinto play on three thase systems ?