Physics: Electricity

Three things to note:

1. The Electric field (E) is a general expression of force - force per unit charge - and voltage (V) is a general expression of unit energy - energy per unit charge. 
2. R ∝ L/A, C ∝ A.D. Think of resistors and capacitors in parallel as having increased width (more capacitance, less resistance) and resistors or capacitors in series as having increased length or distance (more resistance, less capacitance) 
3. Static electricity describes point charge and is like gravity. Current describes moving charge and is like fluid flow. 

Equations: 

• F = k(q1q2/r^2) , Where k = 8.988 x 10^9, and q represents charge. 
• E = k(q1/r^2) , Where E is electric field. 
• F = qE
• U = qEd , where U is potential energy, 
• U = k(q1q2/r)
• V = Ed
• V = k(q1/r) , This is a scalar value. 
• R = ρ(L/A) 
• I = V/R 
• C = Q/V 
• U = 1/2QV or U = 1/2CV^2 or U = 1/2(Q^2/C) 
• F = qvBsinθ

The universe has no net charge. Charge is simply created through the separation of electrons from protons. 

Lines of force in general point in the direction of the field (positive to negative for electric fields, and towards the mass creating the field for gravitational fields 

Voltage (V) is the potential for work by an electric field in moving any charge from one point to another, as described by V = Ed

Charges flow "downhill" from higher potential to lower potential 

Conducting materials will hold excess charge on their surface. Insulating materials will do the opposite. 

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Circuit Elements

R = ρ(L/A) , where ρ is resistivity, and R is resistance. 

I = V/R , where I is charge, and R is resistance. 

C = Q/V , where C is capacitance 

The energy (U) stored in any shape capacitor is given by: 

U = 1/2QV or U = 1/2CV^2 or U = 1/2(Q^2/C) 

Using any one of these equations, the others can be derived from Q = CV 

The dielectric constant K, refers to the substance between the plates of a capacitor. 

*Know between capacitor and resistors series and parallels*

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Magnetic Fields:

A stationary charge creates a magnetic field. A changing electric field creates a magnetic field and a changing magnetic field creates an electric field. 

F = qvBsinθ

*know right hand rule*