the flow of charged particles particles can be

the flow of charged particles; particles can be positive or negative, but usually negative (electrons) through a conducting metal

electric cell - a device that converts one form of energy to electrical energy Chemical cells convert chemical energy into electrical energy. Chemical cells can be “wet” or “dry”.

Solar cells convert light energy into electrical energy. A generator converts mechanical energy into electrical energy. battery - two or more cells connected in series or in parallel

Electric current is measured in Amperes, in honor of Andre Marie Ampere One Ampere is the flow of one Coulomb of charge per second. 1 Amp = 1 Coulomb per second = 1 C/s I = Q/ t

Ammeter a device that measures current Voltmeter a device that measures electric potential difference

power = work/time . = (work/charge) (charge/time) . = electric potential difference current P (Watts) = V (Volts). I (Amps)

Analogies of simple circuits are these links: Water circuit analogy link Air flow link

Resistance determines the amount of current flow = the ratio of potential difference to current V The SI unit of resistance is the I Ohm, Ohm W, named in honor of Georg Simon Ohm R= One Ohm of resistance is the resistance such that one Volt of potential difference is needed to obtain a current of one Amp

The resistance of a circuit element depends on: 1. the length of the conductor as length increases, resistance increases proportionally 2. the cross-sectional area of the conductor as area increases, resistance decreases proportionally 3. the resistivity of the conductor as resistivity increases, resistance increases proportionally

Ohm’s Law The ratio of potential difference to current is constant. If R = V/I is a constant value for a given resistor, then that resistor is said to obey Ohm’s Law. Click here and here to link to pages describing resistor color codes.

Resistivity The resistivity, r, of a conductor is equal to the resistance of a wire 1 cm long and having a cross-sectional area of 1 cm 2. l R =r A R = resistance, measured in Ohms r = resistivity, usually in units of W. cm l = length, measured in cm A = cross-sectional area, measured in cm 2

Many circuit elements do not obey Ohm’s Law. Resistors that get hot, like light bulbs and heating elements, do not keep a constant resistance. Resistance generally increases as objects become hotter. Click here and here to run simulations of Ohm’s Law.

Series Resistor Circuits 1. total resistance is the sum of the separate resistors RT = R 1 + R 2 + R 3 +. . . 2. current is the same through each resistor IT = I 1 = I 2 = I 3 =. . . 3. total potential difference is the sum of each VT = V 1 + V 2 + V 3 +. . . In other words, in a series circuit, resistance and voltage add, but current stays the same.

R, W E = 12 V R 1 R 3 R 2 R 1 8. 0 R 2 2. 0 R 3 5. 0 RT = VT = IT = PT = V, V I, A P, W

R, W E = 12 V R 1 R 3 R 2 V, V I, A P, W R 1 8. 0 6. 4 0. 80 5. 1 R 2 2. 0 1. 6 0. 80 1. 3 R 3 5. 0 4. 0 0. 80 3. 2 RT = 15 Ω VT = 12 V IT = 0. 80 A PT = 9. 6 W

Parallel 1. reciprocal of the total resistance is the sum of the reciprocals of the separate resistors 1/RT = 1/R 1 + 1/R 2 +1/R 3 +. . . 2. total current is the sum of the current through each resistor IT = I 1 + I 2 + I 3 +. . . 3. potential difference is the same across each resistor VT = V 1 = V 2 = V 3 =. . . In other words, in a parallel circuit, resistance adds as reciprocals, voltage stays the same, and current splits.

R, W E = 12 V R 1 R 2 R 3 R 1 12 R 2 8. 0 R 3 12 RT = VT = IT = PT = V, V I, A P, W

R, W E = 12 V R 1 R 2 R 3 V, V I, A P, W R 1 12 12 1. 0 12 R 2 8. 0 12 1. 5 18 R 3 12 12 1. 0 12 RT = 3. 42 Ω VT = 12 V IT = 3. 50 A PT = 42 W

Kirchhoff’s Rules Loop Rule: The sum of the potential differences around any closed circuit loop is zero. Junction Rule: The sum of the currents into any circuit junction is zero. Go to link 1, link 2, link 3, link 4, link 5, and link 6 to view pages and simulations examining Kirchhoff’s Loop and Junction Rules.

The site linked here allows you to build and test your own series, parallel, and/or combination circuits. For a complete interactive tutorial on electricity and magnetism, go here.