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Fig A5
voltage drop across R1 becomes smaller and so the voltage between R1 and R2 is 'pulled
up' towards 5v [Fig A5].
Detailed Explanation
The point of electricity is that it uses electrical current (electrons) to carry energy and so
Electrical/electronic circuits are really just a very flexible means of transporting energy
from one place to another.
'Volts' are a measure of this: the amount of energy carried per electron, which is why the
Units of volts are Joules/Coulomb (because Joules are a measure of energy and a Cou-
lomb is the charge on roughly 6 241 509 324 000 000 000 electrons).
Therefore, when we say that a closed (connected) circuit has 5v on one end and 0v on the
other it means that energy is lost across the circuit. The energy 'lost' is really used to pro-
vide light or switch transistors or move motors or (if all else fails) give off heat.
The power output by a circuit is therefore the energy per electron (Volts) multiplied by the
rate of electrons (the current, in electrons per second). And this is simply:
Joules
Power (
second
Similarly, if we restore R2, then make R1 much smaller than R2, the
) = Volts x Current =
Coulombs = Joules
Joules
x
Coulomb
second
second
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