Direct Current

Definitions:

Matter – Anything that occupies a space and has weight.  It may be a solid, a liquid or gas.  Examples: Rock, Water, Air.   All matter is made up of atomic particles called atoms, and atoms are made up of even smaller particles called Protons, Neutrons and Electrons.

Potential difference – For an equivalent amount of protons in two pieces of matter, one piece will have more or less electrons than the other.  Electrons of an atom can become dislodged and move to another atom whereas the protons and neutrons of an atom stay fixed in place. A negative charge is created when an atom has an extra electron; a positive charge is created when an atom loses one of its electrons to another atom. It is the movement of electrons that create electricity.

Voltage (E, emf, v, potential difference) - Voltage and electromotive force (emf) are terms usually associated with a source of electrical energy such as a generator voltage or battery voltage.  The terms IR drop and voltage drop are used to quantify the voltage applied across individual components of a circuit.

In a DC circuit - Ohms law states that E = I x R.

E = Voltage
I = Current
R = Resistance

In AC circuit analysis, resistance (R) is replaced by impedance (Z).  In addition to resistive properties, impedance takes into account the inductive and/or capacitive reactance in the AC circuit.

Circuit – The path where electrons flow.

Ground – The Earth, the return path of a circuit.

Load – The part of an electrical circuit where the electricity flows to perform work.

Resistance – The opposition to the free flow of electrons in a circuit.

Heat – A byproduct of the transformation of energy.

 

Direct Current

DC Circuit Voltage, Current and Resistance relationships per Ohm’s Law.

• E (electromotive force) represents the voltage, V.
• I  stands for electrical current.
• R stands for resistance.
• P stands for Power.

If the current (I) and resistance ( R ) of a circuit are known, then find the voltage (E) by multiplying the current by the resistance.          

E = I x R

If the voltage (E) and resistance (R) of a circuit are known, then find the current (I) by dividing Voltage (E) by resistance ( R ).              

I = E / R

If the voltage (E) and current ( R ) of a circuit are known, then find the resistance ( R ) by dividing voltage (E) by current ( I).                                

R = E / I

If the voltage (E) and current (I) of a circuit are known, then find the Power consumed in the circuit by multiplying current (I) by voltage ( E ).       

P = I x E

 

	Other relationship formulas: I = P / E               I ² = P / R   E = P / I               E ² = P x R R = E ² / P           R = P / I ² P = I ²/ R              P = E ²/ R

Kirchoffs Laws

Kirchoffs 1st law states that the sum of the currents arriving at any point in a circuit must equal the sum of the currents leaving that point.

Kirchoffs 2nd law states that the sum of the voltage drops in a circuit equals the total applied voltage.

 

DC Circuit Analysis

	Series Circuit The lamp is on. The resistance of the lamp filament is 2 ohms. The battery voltage rating is 3 volts. Calculate the current flow?
	Calculate the current through the resistor. Calculate the voltage drop across the resistor Calculate the power measured in watts
	The switch is in series with the two Lamps. The two Lamps are in parallel with each other. Both Lamps are identical, each one draws ½ amp.  The source is 3 vdc. What is the Voltage across each lamp? A -  When the switch is Open. B -  When the switch is closed. What is the current through the switch? A -  When the switch is Open. B - When the switch is closed