Electrical Principles

Hi I have two question I can't get my head around the first,

Calculator the resistivity of an aluminium conductor 150m in length, csa is 4mm2 and has a resistance of 1.06 ohms.

I rewrote the resistivity formular to give me p= AR/l which gives me an answer of

(4x 10-3 x 1.06) / 150

0.00002826

Think I have this wrapped round my head a little bit

The other is calculation the voltage across the resistor and the inductor

I am not even sure where to start with this one I have worked out the total circuit current and the Impendants of the circuit so is it just ohms laws ? However this would give me it across the circuit, I have been given the information at the power sorce there is 230v 50 hz if that helps at all.

Don't know if you guys can help, thought it might be worth at ask

Cheers

What was the formula you started with for your resistivity calculation first?

Kieron.trollope said:

Hi I have two question I can't get my head around the first,

Calculator the resistivity of an aluminium conductor 150m in length, csa is 4mm2 and has a resistance of 1.06 ohms.

I rewrote the resistivity formular to give me p= AR/l which gives me an answer of

(4x 10-3 x 1.06) / 150

0.00002826

Think I have this wrapped round my head a little bit

The other is calculation the voltage across the resistor and the inductor

I am not even sure where to start with this one I have worked out the total circuit current and the Impendants of the circuit so is it just ohms laws ? However this would give me it across the circuit, I have been given the information at the power sorce there is 230v 50 hz if that helps at all.

Don't know if you guys can help, thought it might be worth at ask

Cheers

Click to expand...

Hi Kieron

You were almost right on the Resistivity question, you transposed the formula correctly but you did not convert the mm2 in to metres correctly 4mm2 is actually 4x10-6 and not -3, because you are converting area here and not length. Its difficult to understand and for me to explain here but draw out a square and label two of the sides 1m each, the area of this square is now 1m x 1m = 1m2. Now draw the same square and instead of metres use the equivalent mm so it will be 1000mm on each side. Now carry out the same calculation 1000mm x 1000mm and what do you get? yes 1000000m2.

so for length 1m = 1000mm

but for area 1m2 = 1000000mm2.

Back to your question if you used your formula it would be ((4 x 10-6) x 1.06)/150 = 2.827 x 10-8 ohms/metre or 0.028microohms/metre.

As for your second question, you should have been given a value for the inductor in Henrys and a value for the Resistor, this would allow you to work out XL and then you can worked out Z using the impedance formula [SIZE=medium]Z = √(R2+XL2). Now you have found Z you can work out current with I=V/Z.[/SIZE]

[SIZE=medium]apologies for the squared value symbols etc but I hope this helps.[/SIZE]

eodneil said:

apologies for the squared value symbols etc but I hope this helps.

Click to expand...

If you're using a conventional keyboard (which you may not be), for squared just hold down Alt and hit 0178 or your numeric keypad.

eg 2.5mm² T&E

Good explanation eodneil

HandySparks said:

If you're using a conventional keyboard (which you may not be), for squared just hold down Alt and hit 0178 or your numeric keypad.

eg 2.5mm² T&E

Click to expand...

Ah great I did not know that, thanks

roys said:

Good explanation eodneil

Click to expand...

Thanks mate

HandySparks said:

If you're using a conventional keyboard (which you may not be), for squared just hold down Alt and hit 0178 or your numeric keypad.

eg 2.5mm² T&E

Click to expand...

?

only works on windoze ?  :C

steptoe said:

?

only works on windoze ?  :C

Click to expand...

Yeah, alt codes is a Windows thing. You can do Unicode characters on Linux (which I'm sure you know as you are computer expert ). Can't remember how OTTOMH so some Googling needed, but the principle is the same, just need 2 or 3 times more keypresses.

Lurch said:

Yeah, alt codes is a Windows thing. You can do Unicode characters on Linux (which I'm sure you know as you are computer expert ). Can't remember how OTTOMH so some Googling needed, but the principle is the same, just need 2 or 3 times more keypresses.

Click to expand...

msl1:

Ive actually got a virtual keyboard dock thingie that lets me do funny symbols 

There's a couple of very good electrical installation calcs books by Watkins & Kitcher, a basic and advanced one. Worth getting.