CH 5 – Electricity and Magnetism Electricity Formulas CH 5 – Electricity and Magnetism

How does this all fit together? The next few slides are ‘enrichment’. They contain topics which are taught and evaluated in the ‘advanced’ science course. It’s a bit silly to discuss the next few topics without contextualizing the whole of electricity and magnetism so…

Static + Mag Action at a distance

Mag Field about a Wire

Solenoids What happens if we use a lot of wire? PhET Generator Simulator https://phet.colorado.edu/sims/html/faradays- law/latest/faradays-law_en.html

Now back to business…

What is Electricity? Electrons flowing through a sample: dynamic electricity Previously, we discussed static electricity, which is a buildup of electrons on a surface

Electrical Circuits For electricity to flow, there must be a closed electrical circuit Circuit def’n: movement (flow) of electrons through a closed pathway

Describing Electrical Circuits In order to properly analyze and investigate electrical phenomenon, we must first define certain variables

Current Intensity Or just Current Def’n: # of charges that flow past a given point in an electrical circuit every second In other words: how many electrons are flowing through the circuit Symbol: I (capital ‘eye’) Unit: A Ampere or ‘amp’ for short Named for André-Marie Ampère Specifically A = 1C/s (enrichment)

Potential Difference More commonly just called: VOLTAGE Def’n: Amount of energy transferred between two points in an electrical circuit In other words: what’s the ‘difference’ between two points on this circuit (not really a good definition) Actually, the proper definition is a bit more advanced: Suppose you have a electrical field, the voltage is equal to the work done per unit charge to move the test charge between two points In other words… suppose you have a field and you want to move an electron from point a to b, the voltage is what you need to do

Voltage Basically…think of voltage, or potential difference, as a difference in terms of electrical circuits Symbol: V ; Unit: V (volt) Small voltage High voltage

Resistance Def’n: the ability of a material to hinder (oppose) the flow of electrical current Symbol: R Unit: Ω (Ohm) named for Georg Simon Ohm Factors that affect resistance: (we’ll discuss more in detail later) Nature of substance: conductors, semi-conductors and insulators Length of wire Diameter of wire Temperature: warm elements = more resistancae

Ohm’s Law Relates V, I and R V = IR This formula is given on the formula sheet Also can be given as 𝑅= 𝑉 𝐼 or 𝐼= 𝑉 𝑅 Again, we’ll discuss more in detail when we get to resistance and conductance, but basically: For a given resistance, the potential difference in an electrical circuit is directly proportional to the current intensity

Ohm’s Law

Power Def’n: The amount of work an electrical device can perform per second Symbol: P Unit: W (Watt) = 1 J/s (Joule per second) In an exam, you will be given V=IR P=IV E=P∆t

James Prescott Joule James Watt

Electrical Appliances

Energy Time Def’n: the ability to do work or affect change Symbol: E Unit: J (Joule) Time Def’n: the total duration of a process Symbol: t Unit: s (seconds) The basic SI unit is the second

Formula Manipulation In an exam, you will be given V=IR P=IV E=P∆t You are not given E=IV∆t but it is easy to derive… substitute P

Unit Conversions Don’t memorize… understand how to derive

Formulas Practice Questions Now time to practice…