Four Chapter 5

Power in Circuits

• Electrons gain energy from the source, and as they move through the circuit, this energy is used up a little at a time at each load.
• Remember that:

E = VIT

• In this equation, E = energy, V = Potential difference, I = current, and T = time
• As with work, the rate of energy loss may be more useful (i.e. power)

Current, Voltage, and Power for Alternating Current

• With alternating current, electric potential (Voltage), and current are constantly changing, and this causes circuits to behave slightly differently.
• Electrons in alternating current circuits move back and forth without getting anywhere.
• Never-the-less, energy is still dissipated in the circuit, even though electrons don't move anywhere
• One Ampere in Alternating Circuits - the current that produces the same heating effect in a given resistor as does one direct current Ampere.
  • For Alternating current,
    • one Ampere (A) maximum current, will not produce as much heat as one Ampere direct current
    • This is due to the fact that the current is not always one Ampere maximum. It fluctuates between +1 A, and -1 A.
    • The effective value for alternating current (I_eff) has been experimentally found to be 0.707 time its Maximum value (I_max). Therefore,

I_eff = 0.707 I_max

• One Volt in alternating current circuits - the electric potential difference that produces the same effect in an alternating current circuit as one Volt in a direct current circuit.
• Similarly for voltage as with current

V_eff = 0.707 V_max

Proof

January 6, 2014