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Posted by Peter David Bruce (Member # 4447) on 11-29-2007, 03:56 PM:
 
Um, hello.
Can anyone please explain ohms law in DUMBEST terms possible please? every wiki description is so long...
Really rather important I know this...
Cheers
 

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Posted by Roger Summars (Member # 4494) on 11-29-2007, 04:53 PM:
 
I'll take a stab at it......

I=E/R

the current in amps (I) you expect to measure flowing through a resistor can be calculated by dividing the voltage applied in volts (E) by the value of the resistor in ohms (R).

So if you want to calculate the current drawn by a relay, you simply measure the resistance of the relay coil, measure the applied voltage, do the math, and you know how much current would be drawn from the battery to energize the relay.

Keep in mind that Ohms Law applies strictly to DC circuits. Things become more complicated when you use alternating current.

Perhaps you have a similar real-life scenario that you would like to discuss?

Roger
 

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Posted by Tim Reed (Member # 137) on 11-29-2007, 05:33 PM:
 
Ohm's Law is the fundamental relationship between the properties that cause electron flow in an electronic circuit.

Here are the basic forms of the relationship:

E=IR

I=E/R

R=E/I

Where:
E=Electromotive Force (i.e., voltage, measured in Volts)
I=Intensity (i.e., current, measured in Amperes)
R=Resistance, measured in Ohms

Voltage (E) is the pressure that causes a current (I) to flow through a resistance (R). A common analogy is that of water flowing through a pipe, with the exception that electrons do not continue to flow if the circuit is open. A pressure (E) causes a certain amount of current (I) to flow through a resistance (R) - based on the amount of that resistance and the value of the applied voltage. If the resistance is great enough (i.e., infinity, or an open circuit), the current flow stops (even though the applied voltage may be constant). The less the resistance, as indicated by the formula, the more current will flow. As the resistance decreases near zero (or, down to the resistance of just the wire making up the circuit), maximum current will flow -- depending on the value of the applied voltage (E).

Current flow will increase if either the voltage is increased, or the resistance is decreased.

Current flow will decrease if either the voltage is decreased, or the resistance is increased.

If any two values of voltage, current, or resistance are known, you can use the Ohm's Law formula to find the missing value.

Hope that's not too obscure.
 

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Posted by Steve Guttag (Member # 268) on 11-29-2007, 05:40 PM:
 
Okay...here we go.

Roger gave you a mix of good and bad info...Ohms law is one of the absolutes in electricity thus it applies to both AC and DC circuits...simply replace the "R" with a "Z" and you get impedance. The real big absolute in electricity is Power in = Power Out...but you didn't ask about power here so lets get into Ohms Law.

What Roger showed in the equations and example are true.

Ohm's law gives you way to express the RELATIONSHIP of current, voltage and resistance (impedance) in any circuit. Providing you know basic algebra, if you know any two pieces of the puzzel, you can find the 3rd. As Roger stated, with AC things get more complicated since you have time variances introduced from the reactive components (inductances and capacitances). Since to work with the AC variants one needs an understanding of Calculus (both derivative and integration), it is highly unlikely that information would be on any test for a projection position...even if in management.

So, as far as Ohms law is for you, the DC version is all that might be asked (or AC with hypothetical non-reactive parts for even wire has inductive and capacitive properties).

So I=E/R (E=Electromotive Force...aka Voltage so it is also written I=V/R). I is current and R = resistance and denotes no reactive components.

Again, presuming you know basic math, don't be confused by alternative forms...V=R*I, R=V/I...it is all the same thing. All you might possibly be asked to do is "Plug and Chug" as we used to say.

It is also possible that "Power" might come up, I guess and be mixed with Ohms Law. Power equalling V*I.

Using some basic algebra you can use that power equation and substitute R*I for V as shown with Ohms law so you get R*I*I = P (Power, in watts). That is, P=I^2*R. Likewise, you could have used the V/R instead of I so you would have had V*(V/R)=P...or P=(V^2)/R.

So there it is in all its likely forms. The rest is your ability to deal with algebra and word problems.

Steve
 

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Posted by Peter David Bruce (Member # 4447) on 11-30-2007, 03:10 AM:
 
well i understand the basics.... maths was never a strong point for me... so hopefully with further training I can get up to scratch on that.

My key strengths for this interview will be my actually approach to the job. Mathematics is always important, which is why i had to ask about ohms. My previous proj manager has helped me out with this... and really I shouldnt have a problem.

I just really want to make this job work for me. in a good way! not commandeering the whole place but just to have the power to guide the company into the future.

Ohms... ok so I=E/R ... if E is reduced and R is increased, I will decrease. And vice-versa. Makes rough sense.

to be truthful, I have already shown my knowledge of the projectors and how they all work, solving issues etc. Plus my ability with the paperwork and Rota etc.... Should bode well.

I will post in my interview topic later how I feel it went. Dont know how long it will take to hear the result.

Only two people have applied for the role, and I am friends with the other guy, so either way it will work out for the better.
 

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Posted by Monte L Fullmer (Member # 2797) on 11-30-2007, 03:25 AM:
 
..to add to the Power thing: I call it the "pie" formula - being P=IxE.

Simply put, Power (wattage) = current (I) times (E) voltage - the simple way we chek how much wattage is the bulb using by taking the amp reading and times it by the DC voltage coming out of the power supply.

When you open a new bulb box (esp with the Christies..) there is a card there that the technician at Christie has written down the initial voltage, current and wattage run on that new bulb ..which is the same as the formula above.
 

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Posted by Peter David Bruce (Member # 4447) on 11-30-2007, 09:23 AM:
 
excellent,. thankyou all so much.

Just had my interview for manager. couldnt have done it any better and I made a good impression. Now its a waiting game.

I really had to show them what i knew about the ohms law and apparently i got it just right! whoo!
 

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Posted by David Graham Rose (Member # 1450) on 12-01-2007, 03:08 AM:
 
y=ASin(wt+/-phi)
 

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Posted by Peter David Bruce (Member # 4447) on 12-01-2007, 12:15 PM:
 
ok now im confused.
 

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Posted by Chris Slycord (Member # 4239) on 12-01-2007, 12:35 PM:
 
That's the equation for AC voltage time dependence

V(t) = Vm * sin (wt + phi)
Where Vm is max/peak voltage
w is angular frequency; same as 2*Pi*f where f is the regular frequency
And phi is the phase difference between current and voltage.
 

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Posted by Jon Miller (Member # 163) on 12-01-2007, 09:18 PM:
 

quote: Monte L Fullmer

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..to add to the Power thing: I call it the "pie" formula - being P=IxE.

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