Science & Mathematics » Physics » I've been given 'power' for homework after olms law. How much about power should I get to learn for homework?

# I've been given 'power' for homework after olms law. How much about power should I get to learn for homework?

Hi, I am attending college and doing electrical installation level 1. We have just done olms law which was very very easy.

He just drew an empty triangle on the board with 'power' next to it. Then said take a photo of that and then use google to do it at home basically.

Surely he must be expecting us to do more homework than just learn to multiply voltage by current though lol.

• P = iV. and also P = i^2 r
I don't know what your teacher wants you to do. You should ask him.
1
0
• Power = V*I = V*V/R = V²/R OR V*I = I*R*I = I²R
This applies to the power dissipated in a resistance R
1
0
• Power has many implications for your study.
OK we know that it is VI
but how is it affected by other things.
When you put it through a wire there is resistance in the wire and in the load.
So that there are SOME volts in the wire and some in the load.
The volts in the wire cause HEAT ( a serious issue )

if power = V * I and V/R = I then power = v^2/ R , power = I^2 R

Hence the heat in the wire is proportional to the square of the current.
ie if you have a cable rated at 10A with a 30C rise above ambient and you put through 20 A then the wire would be at 4*30 = 120C above ambient temperature. OUCH.

If the heat cannot escape because some moron has left the wire coiled then the temperature rise can be many times higher. Call the fire brigade now.

Equally if the wire in the wall or ceiling is covered by insulation then the same thing happens.

These are things that you should absolutely know before you would dare to install any power cable anywhere at any time.
0
0
• E=I*R is ohms law, But P=E*I is watts law. They are very similar but you don't want to mix them.
Go to a library and start checking out books on AC Power and even DC power.
Text books are good if you can find them, they organize things well and are designed for learning. You may also ask the instructor for recommendations on what to read, He probably has favorites, read those.
0
0
• Where i is current and e is voltage and r is resistance:

P = i e. Using Ohm's Law, P = ( i^2)R. Also, using Ohm's Law, P = (e^2)/R.

Having observed many power outages, I've come to the conclusion that power is measured in a unit called outage (I'm joking...it is really Wattage).
0
0
• Electrical Installations sounds like it will involve AC circuits. In an AC circuit, the rms values for voltage, V, and current, i, as read from standard AC meters will give an average power of i^2R or iVcosA, where A is the phase angle between voltage and current . This could be represented on a triangle with iV as the hypotenuse and i^2R as the adjacent side.
1
1
• Power is defined as ampere which is electronic charge flowing per seconds in a conductor.
Ohms law states that the electric field is directly proportional to the Current density on a per per unit area basis.
I = current= voltage x velocity, where resistance has the Units of inverse velocity
In ac current impedance is defined as the sum of Resistance + Reactance
0
1
• First and foremost, learn how to spell OHMs Law.

If you can spell it correctly, you can look up information.
0
0
• Average Power is the integral of VI dt divided by time. In sine wave AC circuits where the phase between voltage and current is shifted, the power is negative for a portion of the sine wave cycle so the average forward power is VI cos theta, aka the "Power Factor". Since we use sine wave AC power so much, it's important to know the shortcuts. It's interesting to see that the total power is always the sum of the power of all the frequencies present, including 0Hz, aka DC offset.
https://www.electricaltechnology.org/201...
0
0
• a word of warning -

ohms law is fine for DC - but it dont work so well (if at all) for AC

So what figures exactly are you gonna be using for volts and current when both are alternating AND varying in peak values

AND are feeding a non-resistive load?

(and you have to be careful using RMS values- cos this only applies in specific circumstances)
0
0