Electric Laws And Relationships

​Electric Laws & Relationships

EF Ch 12 ​Slides 14-31- Electric P2

Kirchhoff's Current Law

The law states that at any given time, the sum of currents that are entering a node must be equal to the sum of the current leaving the node

A node is any location or junction where the current may split, branch, or combine​

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nodes don't have pockets​

​I _in = I _out

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​I'm a genius, really.

When the total of a quantity is constant and unchanged over a system, we can say it is conserved​

​Conservation

what is going into a node must equal to what is leaving​

​Basically

​Kirchhoff’s Current Law

Resistivity

The resistivity values are usually measured using samples made of a 1 cm cube or a cylinder having a diameter of 1 mil and length of 1 ft

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The resistance of the sample is then given by

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It's measured in Ohms.​ Ω

​Electrical Resistance

Electrical resistance of a material varies with temperature

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Resistance of conductors increases with increasing temperature

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Superconductivity exhibits near-zero resistance at very low temperatures (approaching absolute zero)

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Protect sensitive components or to control the flow of current in a circuit

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Divide or control voltages in a circuit​

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​Uses in Circuits

resists the flow of either direct or alternating current

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​Electrical Components

​Resistors

​Resistors

can have a fixed value or variable

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dissipates heat as electric current flows through it

amount of heat depends on the resistance of the component and the amount of current ​flowing

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variable resistors ( aka potentiometers) are used to allow adjustments like dimmer switches and volume controls

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Multiple Choice

Resistors are electric components that can resist or control flow of direct current only.

• False

• True- alternating current is completely out of control and that is why it was used to euthanize elephants

​Electrical Wire Resistance Varies with Size

The electric resistance of a wire increases as its diameter decreases - like drinking through a milkshake straw vs. a coffee stirrer

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​AWG ( American Wire Gage) is used to represent wire diameter size

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​AWG

The smaller the AWG number, the bigger the wire diameter

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​National Electrical Code

Describes wire types, maximum operating temperatures, insulating materials, outer cover sheaths, type usage, and the specific location where a wire should be used

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Multiple Choice

What would increase the resistance of a conductor?

• Finally getting Swifty tickets

• increases in temperature or the addition of heat

• decreases in temperature or the removal of heat in the range of 32 degrees F

Multiple Choice

What does this symbol represent? Ω

• voltage

• current

• AWG

• resistance

Multiple Choice

Smaller AWG numbers result in what relative size of wire?

• identical

• larger

• smaller

• I'm not even reading these

​Capacitors

have two oppositely charged electrodes with a dielectric material inserted between the electrodes

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​Capacitors

​Used in many applications to serve as filters to protect sensitive components in electrical circuits against power surges

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​Capacitors

Used in large computer memories to store information during a temporary loss of electric power to the computer

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​Used in tuning circuits for radio receivers, audio filtering applications, timing elements for strobe lights, and intermittent wipers in automobiles

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​Capacitors

Unit: farad (F)

one farad = 1 coulomb per volt

capacitor sizes are commonly expressed in ϥF or picofarad (10^-12 F)

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​Ohm's Law

voltage, resistance, and current are related through this equation:

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V= R x I or volts = ohms x amps​

if you know two, you can figure out the last one and because of me your teachers will be able to give you a bunch of electrical problems

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YOU'RE WELCOME!​

​V = I x R

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​Nope, I'm the genius.

Multiple Choice

What is units are most commonly used to express the quantity of current?

• volts

• amps

• ohms

• watts

Multiple Choice

Who is credited with determining that electric current is conserved at nodes?

• Ohm

• Kirchhoff

• Edison

• Tesla

Multiple Choice

What component is used in tuning circuits for radio receivers, audio filtering applications, timing elements for strobe lights, and intermittent wipers in automobiles?

• AWG 50 wire

• batteries

• capacitors

• kirchhoff

Kilowatt hour (kWh) units are used

in measuring the rate of

consumption of electricity by homes and business

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​1 kWh = amount of power consumed during 1 hr by a device that uses one kW, or 1000 joules (J) per second

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​kWh

where

P = power in watts

V = voltage in volts

I = current in amps

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​P= I x V

​Electric Power

Multiple Choice

What is units are most commonly used to express the quantity of power?

• volts

• amps

• ohms

• watts

Multiple Choice

Which is another correct form of Ohm's Law?

• V x R = I

• V x I = R

• V / I =R

• P = R x I

The total resistance is the sum of the resistance in the circuit

R _total = R₁ + R_2​ + .....

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​Resistance

The voltage drop across each element can be determined using Ohm’s law

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The sum of the voltage drop across each element is equal to the total voltage supplied to the circuit​

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​Voltage Drops

​Series Circuits

​With a series circuit, if one of the element fails, the entire circuit fails

The voltage is the same

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The current is divided - use Ohm's law to figure it out ​

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​Across branches

​Parallel Circuits

Prevents all or nothing issue

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Used when wiring electrically different zones ​

​Practical uses:

​Parallel Circuit