Define the interrelation between P,V,I and R.
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Answer:
Answer. In the next tutorial about DC Circuits we will look at Ohms Law which is a mathematical equation explaining the relationship between Voltage, Current, and Resistance within electrical circuits and is the foundation ofelectronics and electrical engineering. Ohm's Law is defined as: V = I*R......
Ohm’s law comes in two basic parts from which all others can be derived. It mathematically states the relationship between current (I), voltage (V) resistance (R), and power (W). The units respectively are amps (A) volts, (V) Ohms (Ω) - that last character is Omega, the last one in the Greek alphabet- and Watts (W).
It gets a bit confusing because the scientific types use a slightly different form from the technical ones. In technical we put the first part as:
V = IR
which simply means voltage = current times resistance (but you have to remember to put the current in amps and resistance in ohms, so 500 mA would be 0.5A and 200 kΩ would be 200,000 Ω).
In scientific circles this would be:
E =IR
which is exactly the same thing, as in pure (rather than applied) physics they call a voltage an electro-motive force. Which is exactly what it is. Current is in fact a function of voltage and the resistance it encounters, as you might see if you transposed. Usually, in the real world, we know the applied voltage and resistance and what we are concerned with is finding current, and so let’s transpose:
As V = IR then V/R =I.
For example, if I wish to supply 10V to a resistive load of 8Ω, I do 10/8 to get 1.25A and I’d better make sure my wires and other bits can cope with that. Before we go on to the second part, I hope it’s clear that a current is caused by a voltage meeting resistance. The lesser the resistance, or the greater the voltage, the more current. There is a special case where resistance is equal to zero. In technical we seldom encounter it, and largely ignore it, but physicists working with superconductors do encounter it. At very low temperatures, some conductors form frankly weird things called Cooper Pairs, and can cause current with zero (or as near as makes no difference) resistance.
The second part is the classic equation known to every electrician since two days into their training:
W = AV or Watts = Amps times Volts. In scientific, they write:
P=IE (Power = Current times Electromotive Force)
In technical we are often concerned with the power, which we name the wattage, dissipated through a resistive load as more power leads to more heat. Too much heat means your wires or bits will burn. Taking our example above, 1.25A and 10V, we would have 12W. That’s quite a bit for electronics and we’d have to find a way for our load to cope. We could use an n by n network to dissipate power safely or simply stick in a load that is capable of handling 16W or more (always leave a good bit of margin).
As you might see, the relationship hinges on the applied voltage and the installed resistance. If you remember V=IR and W=AV then you can work out from any two what the other two will be.
Ohm’s law is linear, and so it works for any purely resistive load under AC or DC. It works in modified forms for reactive (containing capacitive and inductive under AC) loads too. However some conductors are non-ohmic. You don’t meet them often, and usually you refer to tables to see what they do.