Ch+17+-+Current+and+Resistance

//This chapter adds to the last by making the charges flow. This involves the mechanical speed of the charge carrier (typically electrons), drift speed; and the electrical speed of the charge flow, current. Current is then related to the resistance of a circuit, bringing into play Ohm's Law and the Resistivity equations. Since the chapter begins with moving charge, it ends with "moving" electrical energy: power.//
 * Chapter 17: Current and Resistance**

[|Equations:] I =ΔQ/Δt I = nqvA V = IR R = (rho)l/A (rho) = (rho(not))[1 + (alpha)ΔT] P = IV = I²R = V²/r

//New Quantity:// __Current__- the rate at which charge flows through a perpendicular cross sectional area. Measured in Amperes (A). I =ΔQ/Δt //where Q is the amount of charge that passes through the area at a time t// Amperes = Coulombs/second
 * Electric Current:**



Both positive and negative particles can flow but //**the book will always use conventional current, denoting the direction that positive charges would flow.**//

ΔQ = number of carriers X charge per carrier (nAΔx)q //where// ΔQ is the mobile charge, //n is the number of mobile charge carriers, A// Δx is the volume of the object, and q is charge on each carrier.
 * Current and Drift Speed:**

__Drift Speed__- an average speed at which the carriers move. //by substituting// Δx = vd Δt into the equation above we are left with: ΔQ = (n*A***vd***Δt)q //which can then be simplified to:// I=ΔQ/Δt=n*q*vd*A

__Cicuit__ - a way a stating that current flows in a closed loop/ complete path of conductors __Battery/Cell__- a power source that pushes electrons around __Circuit Diagram__- a standard, well know way of showing a circuit, its path, and parts using block formation __Multimeter__- a meter used to measure voltage, current, or resistance //voltmeters and ammeters can be stand alone devices as well//
 * Measuring Current/Voltage in Circuits:**
 * Voltmeter- measures potential difference (volts)
 * used in series of object measuring
 * Ammeter- measures current (amps)
 * used in parallel of object measuring

__Resistance__- as voltage is applied to a circuit, current is proportional to this voltage by a constant called resistance ΔV=IR, R ΔV/I, I ΔV/R //where// //ΔV is// //potential difference, I is current, and R is resistance//
 * Ohm's Law & Resistance**//**:**//

__Resistor__- a conductor that provides a given resistance to an electric circuit Resistors are made up of various values and tolerences. This is so that they can be applied into the circuit and work collectively with other components. On a resistor there are 3 colored lines and possibly a forth line that is either gold, or silver. These lines are what determine the resistor's value. The first two lines correspond to a number value and then the third determines number of zeros at the end of the number, and thus whether or not the value is in ohms, kiloohms, megaohms and ect. The color code can be seen below:

0 - Black 1 - Brown 2 - Red 3 - Orange 4 - Yellow 5 - Green 6 - Blue 7 - Violet 8 - Grey 9 - White

Then there is the 4th line which dictates the tolerance level of the resistor. This means how accurate the resistor will be, and the color code and values can be seen below: 5% - Gold 10% - Silver 20% - No line

Gold being the best tolerance level and thus the resistors having greater accuracy, which means that when a resistor says that it is 5 ohms it is nearly 5 ohms within a 5% range. Credited to Electronic Hobbyists Corner

When a material has a constant resistance regardless of voltage, it is called "Ohmic". Materials whose resistance changes with voltage are said to be "nonohmic".

Resistivity is a proportionality constant "p" used in the formula R=p(l/A) to find resistance "R" when "l" is the length of the material and "A" is the cross sectional area. As temperature of the object increases due to the current, the resistance of the object will also increase. The formula used to find resistance after change in temperature is R=Ro[1 + (alpha)(T (final) - T (initial))] when Ro is the original resistance and alpha is a constant called the temperature coefficient of resistivity. The resistance of some metals will fall to almost zero when the metal is cooled below a certain "critical temperature". These metals are called superconductors. Something that is very different about superconductors is that after a current is set up inside them, the current will continue to exist even without any voltage. This is able to occur, because the resistance is nearly equal to zero.
 * Resistivity:**

Given by the formula: power = I*V I^2*R V^2 / R. Power **i**s the rate at which energy is transferred to the load in the system. This is important, because electric bills are based off of the rate a household must pay per kilowatt hour. A kilowatt hour is the kilowatts of power used multiplied by the time (in hours) it was used. To find the cost, this is then multiplied by a rate such as $.10 per kilowatt hour.
 * Electrical Energy and Power**