Coulomb's Law

The electric force acting on a point charge q₁ as a result of the presence of a second point charge q₂ is given by Coulomb's Law :

where ε₀ =permittivity of space

Note that this satisfies Newton's third law because it implies that exactly the same magnitude of force acts on q₂ . Coulomb's law is a vector equation and includes the fact that the force acts along the line joining the charges. Like charges repel and unlike charges attract. Coulomb's law describes a force of infinite range which obeys the inverse square law, and is of the same form as the gravity force.

ohm law & joule law

lenz law

Henrik Lenz>> German-born

 

Click to enlarge image

 

Circle Laws

Kirchhoff's Laws for current and voltage

The total current flowing into any DC circuit node, also called a branch point, is always the same as the total current flowing out of the node. An example is shown in the top illustration. There are four current-carrying conductors ( a , b , c , and d ) leading into the node (black dot), and two conductors ( e and f ) leading out. Direct currents in parallel add together arithmetically. Therefore, the total current flowing into the node is a + b + c + d , and the total current flowing out is e + f . These total currents, according to Kirchhoff's First Law , must be equa

 

 

Kirchhoff's Second Law deals with voltage . An example is shown in the bottom illustration. A source having voltage equal to a is connected in a circuit with five passive components having voltage differences b , c , d , e , and f across them. The voltages across the passive components add together arithmetically because they are connected in series. According to the Second Law, the total voltage across the set of passive components is always equal and opposite to the source voltage. Therefore, the sum of the voltage differences across all the circuit elements (including the source) is always zero

Ohm's Law

Ohm's law (named after the German physicist Georg Ohm) defines the relationship between Voltage, Current and Resistance E = I x R where:    E is the electrical potential (voltage), measured in volts (V),     I is the current, measured in Amperes (Amps/A), and     R is the resistance, measured in Ohms (Ω). Joule's law states that P = E x I where:    P is Power, measured in Watts The combination of Ohm's law and Joule's law gives us 12 formulas where 2 of the 4 variables are known. The wheel below is a handy tool and memory jogger. To use it, simply choose the quadrant corresponding to the variable you want to calculate, then select the segment corresponding to the variables that you know the values of