Electricity & Magnetism Where science and magic meet

Electricity is the flow of electrons, described as an electrical current. Electrons are negative, so the electrons move from a negative pole towards a positive pole. Electricity can be described as the forces between charges.

Circuits A circuit describes the path that electrons flow through. If there is a break in the circuit, the electric current will not flow.

Circuits An incomplete or broken circuit is said to be an “open circuit”. A complete circuit is called a “closed circuit”. Switches are devices designed to make a circuit open or close.

Oops! A short circuit occurs when the electrical current finds a “short cut” across the circuit. When this happens, the electricity jumps across the path of least resistance, and the designated work, or load, is not accomplished.

What about it? While the study of electricity is relatively new (less than 200 years), a great deal of investigation has been done recently Due to innovations in the modern electrical world (1920 –)

Charges A charge is a point source of electrical force. There are only two charges; Positive and Negative.

Rule of Charge The Rule of Charges is stated: “Opposites Attract, Likes Repel”

Charges in the world Most common objects are neutral (having the same number of + and – charges) An object which has more of one charge than another is said to be charged.

Shocking! The buildup of charges on an object is static electricity. When the static charges do move, it is called an electrical discharge (the charges move along the path of least resistance).

Shazam! Lightning is a form of electrical discharge. The static charges are formed when the particles inside the storm cloud rub against each other, separating charges.

Lightning

How to charge Induction –Bringing a charged object near an uncharged object causes the like charges to run away and attracts the opposite charges –Give the like charges an “out”, leaving the opposites

How to charge Conduction –Touching a charged object to an uncharged object causes the charges on the charged object to spread through the two objects

Voltage Amount of PE that each unit of electrical charge has V= I x R Voltage (volts)=Current (amperes) x Resistance (ohms)

Power Power is measured in Watts (W) Power = Voltage x Current W=Volts x Amps

Ohm’s Law Describes the mathematical relationship present in most circuits

Current Quantity that refers to the rate of flow of electric charges I = V/R Current = Voltage/Resistance Amps = Volts/ohms

Resistance Conductor – allows the flow of electrons Insulator – DOES NOT allow the flow of electrons

Resistance The measure of an object’s ability to conduct electrical current R = V/I Resistance = Voltage/Current Ohms = volts/amps

What is the difference between placing a 1.5 V battery or a 9 V battery in a circuit?

Increase the amt. of current flow ? Greater voltage battery or more smaller batteries Shorter, thicker wire More conductive metal Light bulb with lower resistance

Decrease Resistance? Shorter length wire More conductive metal Thicker wires

Resistance & Current High resistance = low current Low Resistance = high current

Add VoltageAdd Voltage

Open or closed circuit ?

One bulb Single Resistance Full current

Two bulbs Double the resistance ½ the current

Three bulbs 3 times the resistance 1/3 the current

SeriesSeries

Series Circuit

Series or Parallel ?

Series Circuit Current only follows one path Amount of energy used by a circuit must equal the energy supplied by the battery Ex: cheap X-mas lights

Parallel Circuit Current has two or more possible paths Each path is called a branch Same amt. of current must flow out again Ex: your house (ask me to explain!)

ParallelParallel

Parallel

AC or DC ? AC or alternating current – direction of the current goes back and forth In the US, most electrical systems have a current that reverses 60 times per second Ex: your house

AC or DC ? DC or direct current – current that flows in one direction Ex: a battery

Ground wire For safety Connected to the ground near your house Ex: if your fridge has a short circuit, then the electricity will flow into the ground instead of through YOU!

Nikola Tesla Physicist, Mechanical Engineer Many investigations w/ AC AC is easier to produce and cheaper to use