Electricity and Magnetism unit

Concept Map Electrostatics Electricity Magnetism Electromagnetism Electrostatics and Magnetism are both natural phenomena which were manipulated by and for technology

Electrostatics - overview Natural phenomena Obeys law of opposites where the terms negative and positive were selected to indicate the two opposites Materials are divided into Conductors and insulators

Electrostatics - charging By friction - electron affinity Induced Charge Separation (occurs before charging) Grounding - connecting to the earth contact

Electrostatics - 3 keys size of the Charge difference Distance between opposite charges Conductivity of the medium between the opposite charges

Electrostatics - pre 1900 Charges either positive and negative - Ben Franklin positive charges flow to balance out the negatives negative charges “aren’t bad”

Electrostatics - post 1900 Protons and electrons are discovered negative electron is free to move and is the charge carrier (transfer) Positve proton is fixed in the nucleus of the atom

Electrostatics - charge difference Charge difference (symbol Q) is measured in coulombs (Unit C) Charge difference is a reflection of the number of excess/deficit electrons in matter - Q=Ne N - number of excess/deficit electrons e - charge of 1 electron x C charge of 1 proton x C

Electrostatics to Electricity Electrostatics is unpredictable Volta was able to create a small charge difference that was predictable with a wet cell (primitive battery)in 1793 moving electrons can now do work for some application (motor, light, heat)

Electricity - Circuits A loop is created where the electrons can flow from the power supply (battery - origin of the charge difference) to one or more loads. A wire, a highly conductive medium, provides the path for the electrons

Electricity - Circuits Battery/Power supply Q = Ne represents the charge difference E =VQ represents the work/ potential energy that these electrons possess E -Energy(J, Joules) V - Voltage, Electric Potential, Potential difference(V, Volts)

Electricity - Clarification E=VQ should really be ΔE = ΔVQ ΔE reflects the change in energy as the electrons do their work ΔV is called potential difference or voltage, where V is just called electric potential. In Grade 12, we will clarify their differences.

Electricity - Circuits Current (I measured in Amps,A) reflects the moving energy of the electrons. This energy is lost at the loads (applications) Instead of measuring their kinetic energy directly, current measures the amount of charge that moves past a given area in a second I = Q/t

Electricity - Circuits Resistance is a measure of how much opposition the electrons experience as they move throughout the circuit. Sometimes this resistance is desired as it does work on the load. Sometimes it is not desired as seen the energy loss within the wire itself

Circuits - Resistance Resistance at the load (symbol R, unit - Ohm,Ω) - R = V/I Resitivity in the wire

Resistivity - factors the type of metal (gold is the best conductor) the length of the loop the cross sectional path (thickness) the temperature (higher the temperature of the wire the higher the resistance)

Resistivity - Equation R – resistance, L – length, A – cross sectional area The coefficient “ ρ” depends upon the material. Values can be found in Table 13.1 of your PRACTICE PROBLEMS sheet.

Resistance at the load The total resistance in the circuit dictates the voltage and current based on the limits of the power supply. The greater the resistance, the greater the need for energy (E=VQ) to pull one electron around the loop. This results in less electrons completing the loop (I ↓). (and vice versa)

Resistance at the source We first look at the total Resistance in the circuit at the power supply The Power supply’s overall resistance R T controls the size of V T and I T Ohm’s Law applies R T = V T /I T.

The total Resistance in the circuit, mirrored at the power supply, must be equivalent to the loads Each load will have its own resistance R # controlling the size of V # and I # Ohm’s Law applies R # = V # /I # Resistance at each load

Depends on how the loop is created Rules have been established to distinguish between a series circuit, parallel circuit and a mixed circuit. - tomorrows lesson Resistance in the circuit

Power Power is defined as the rate at which work is done. P = W/t (1 W = 1J/s) or P = VI (1 W = 1V∙A) Note: W =ΔE

Power in the home Homes use energy, not power. Power rates how fast energy is used. However, because the loads are often listed by their power requirements – 60 W light bulbs – Electrical companies will measure ones energy use through the KW∙h instead of J. Therefore, using an appliance for 1 hour might require 1 KW∙h or 1 KJ.