Help with some questions

[Simonslimline]

I did it like this, but am not sure i am going about it correctly. I am sure i will stand corrected.


3.58V ÷ 2.5A = 1.432Ω.

1.72 ×10−8 x 500 = 8.6 ×10−6.


8.6 ×10-6 ÷ 1.432 X ×10 3 = 6.005586592 ×10-3.

 

[telectrix]

same as you for R. then

p = 0.026 /sq.mm for 1m length, so

A = (0.026 x 500) / 1.432 = 9.25sq.mm

could be wrong.

 

[happysteve]

6mm is correct:

R = resistance (Ω)
V = voltage (V)
I = current (A)
ρ = resistivity of copper = 1.72 x 10[SUP]-8[/SUP] Ωm
L = cable length = 500m
A = cross sectional area (m[SUP]2[/SUP] ... will need to convert this to mm[SUP]2[/SUP])

R = V/I = 3.58 / 2.5 = 1.432 Ω

R = (ρL) / A, so A = (ρL) / R

A = (1.72 x 10[SUP]-8[/SUP] x 500) / 1.432 = 6.0056 x 10[SUP]-6[/SUP] m[SUP]2[/SUP] = 6mm[SUP]2[/SUP]

 

[telectrix]

arrgggh. i did the sum right, but confused with Al cable as q.3. so used wrong value of p.

 

[telectrix]

happy, where do you get the 10 -8 etc. so it types right?

 

[Simonslimline]

happy, where do you get the 10 -8 etc. so it types right?

I was wondering this as well.

 

[telectrix]

i can do 10² , 10³, but that's about it.

 

[Simonslimline]

For question 2 i get 128.5 metres.

Anyone come up with the same roughly?

 

[telectrix]

for any question now i get 4 pints so don't feel like overtaxing my little grey cells.

 

[telectrix]

For question 2 i get 128.5 metres.

Anyone come up with the same roughly?

128.6, ,,,,

 

[Simonslimline]

Question 3 i make 227volts at the motor terminals. Anyone come close to this answer also?

 

[telectrix]

i got VD of 2.98V, so agree with 227V at load.

 

[telectrix]

Q.4. where's the bloody OP gone after all this hard work on his behalf.

 

[Simonslimline]

i got VD of 2.98V, so agree with 227V at load.

Yep a VD of 2.98125v

 

[stekel]

Hi Im back after a heavy day with the kids ha. All this help is much appreciated.

Right so for question 1 I got R=V/I=3.58/2.5=1.432Ω A=Πxr²=3.142x1.432²=6.44A

And for question 2 I got R=V/I=11.5/13=0.88Ω L=RxA/P=0.88x2.5x10-6/1.72x10-8=
0.0000022/0.0000000172=127.9L

And for question 3 I got R=V/I=230/45=5.1 V=IxR=45x5.1=229.5V