CHAPTER 19. ELECTRIC CIRCUITS 19.5
In addition to voltage and current, there is another measure of free electron activity in a
circuit: power. Power is a measure ofhow rapidly a standard amount of work is done. In
electric circuits, power is a function of both voltage and current:DEFINITION: Electrical Power
Electrical power is calculated as:P = I· VPower (P) is exactly equal to current (I) multiplied by voltage (V ) and there is no extra
constant of proportionality. The unit of measurement for power is the Watt (abbreviated W).Activity: Equivalence
Use Ohm’s Law to showthat:
P = V I
is identical to
P = I^2 R
and
P =V^2
R
Chapter 19 — Summary
See the summary presentation ( Presentation: VPmmk atwww.everythingscience.co.za)- Ohm’s Law states that the amount of currentthrough a conductor, atconstant temperature, is
proportional to the voltage across the resistor. Mathematically we write V = I· R - Conductors that obeyOhm’s Law are called ohmic conductors; thosethat do not are called
non-ohmic conductors. - We use Ohm’s Law to calculate the resistance of a resistor. R =VI
- The equivalent resistance of resistors in series (Rs) can be calculated as follows:
Rs= R 1 + R 2 + R 3 + ... + Rn - The equivalent resistance of resistors in parallel (Rp) can be calculated as follows:
1
Rp=
1
R 1 +1
R 2 +1
R 3 + ... +1
Rn- Real batteries have an internal resistance.
- Wheatstone bridgescan be used to accurately determine the resistance of an unknown resistor.
Chapter 19 End of Chapter Exercises