Monday, February 17, 2020

VQ = Energy, VI = P - III (Fundamnetal Questions)

The first Post of <VQ = Energy, VI = P>ended (not concluded) as

"
We can make a simple modification of the equation VQ = Energy, we can get

V = Energy / Q , or

Voltage is Energy per Charge.

"

Meanwhile as I repeatedly used the following equation.

                        dQ
I (current) =  -------
                        dt    


In both equations Q appears. So we can play with these two equations and Q.

<VI = P> is fine but can we simply multiply V by I ?  Or V times I is possible ?  We can do on paper but is this actually or physically or electrically possible ?

It dos not seem allow us to do <V x I > as the units differ. <V1 +/-V2>、<I1 +/-I2>are OK (while V1 x V2, I1 x I2 will be OK?)

On paper or in our head

                 Energy           dQ
V x I =     ---------   x   --------
                    Q                 dt

                Energy x  dQ
         =    -----------------
                    Q x dt

                 Energy
         =   ------------- (= Power = the time ratio of Energy)
                     t

as I (current) is the time ratio of Q flow (movement)

<V x I > will be the time ratio of Energy <flow (delivery)> or use, storage.

In terms of words

<work >is usually used as <work (is) done> and seldom used as <work will be done>or <potential work>while <energy>is usually used as <energy is (has been) used> as well as <power>as <power is (has been) used>.  But <energy>and <power> also used as <to be used>and <potential energy / power>are quite natural usage.

Potential energy / or potential power makes work done.
Work needs energy / or power to be done. (Work to be done needs energy / or power.)
Work is more like <result> while Energy and Power are more like <cause>.

---------
Through  x  Across

<Through  x  Across>can be imagined as multiplication or product and has some meaning even the units differ.
       
       ^  V
       I
       I
       I
<--------> I or Q
       I
       I
       I
       v

For instance the vertical line indicates V (Voltage) and the horizontal line indicates I (current).  <V x I>indicates the area (like Vcm x Icm = VIcm2). The (area) size of VIcm2 changes when V or I changes or both change. The problems are

1) the units of V and I differ. V in Volt, I in Ampere. So VI = VI Volt-Ampere.

2) I is the time ratio of Q quantity, either constant DC or periodically changes (AC) including the change of direction. This seems to make things complicated. The point is that either direction of current flow work is done - Power or Energy is used.

We can say the same thing to QV = Energy

1) the units of V and  differ. V in Volt, Q in Coulomb. So VQ = VQ Volt-Coulomb.

Another point is that Q moves when work is done. When Q stays and does not move work cannot be done.  Voltage is basically potential but make Electric Field ( a kind of Field Theory). The unit of  Electric Field Strength (measurement of Electric Field) is V/m. <m> is meter so this show the distance between the two points which leads to  the difference. When Q moves or I flows in the Electric Field made by V work is done.. But what makes Q move or I flow. The above sketch can be changed to

       ^  V+
                  
       
<--------> I or Q
     

        v
        V-

The space represents the electric field. (we do not elaborate here but the current flow or more correctly the change of current flow (di/dt) produces voltage - Electro-Motive Force)


Another drawing

                          ----
  ^  ----- I   Load    I --->
  I                       -- --                 I        
 -  (+)                                                I
 V                                                        I        
 - (-)                                                  I                                                     
  I                                                     I
<------------- V
      
Arrows show the direction of Current or movement of Q. Load is usually use Energy or Power like a Resistor (Heater), Light Bulb or LED Lamp. Generating Heat or Emitting Light can be said as "Work is done" and therefore " Energy and/or Power are used". If "Work is not done" then " Energy and/or Power have not been used yet".

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