Electricity and Magnetism Physical Science

Electrical Force The force of attraction and repulsion that either pushes or pulls electrical charges

Electrical Charges Two Types Positive Charge (protons) Negative Charge (electrons) Overall charge of an object is determined by electrons Neutral charge means number of protons equals number of electrons

Electrical Field Area around a charged particle Exerts the force that causes other electric charges to be attracted or repelled.

Force of Attraction Object with different charges will move towards each other (attract) Ex: positive and negative come together

Force of Repulsion Object with like charges will move away (repel) one another Ex: positive will repel a positive

How does a particle become charged? Gain or lose electrons Lose electrons = positively charged Gain electrons = negatively charged

Static Electricity Is the build-up of charge on the surface of an object Transfer methods: friction conduction induction Static Discharge Occurs when a pathway through which charges can move suddenly Ex: rubbing socks on carpet then touching a doorknob

Methods of Charging Charging by Friction Done by rubbing objects together Ex: Rubbing a balloon with hair Balloon gain electrons Hair loses electrons

Methods of Charging Charging by Conduction Charging by touching Ex: Negatively charged object touches neutrally charge object Negative object transfer electrons to neutral object Both objects are negatively charged Weaker than the original negative charge

Method of Charging Charging by Induction Transfer of charge without contact between materials Ex: Neutral doorknob and negatively charge hand When hand is brought close to doorknob, the charges rearrange

Electric Current Continuous flow of electric charge Flows in a single direction Two Types Direct Current (DC) Alternating Current (AC)

AC vs DC Alternating Current Direct Current AKA: AC Flow of electric charge that regularly reverse its direction Ex: homes & schools Direct Current AKA: DC Charges flow in one direction Ex: battery-operated devices

Current Flow of electrons through a wire Increase of current means more electrons flowing in the wire Unit: ampere/amps (A)

Resistance Opposition to the flow of charges in a material Unit: ohm (Ω)

Voltage AKA: Potential Difference Difference in electrical potential energy between two places in an electric field Unit: volts (V)

Conductors vs Insulators Electrical Conductors Is a material through which charge can flow easily Ex: copper, silver, metals Electrical Insulators A material which charge cannot flow easily Ex: Wood, plastic, rubber, air

Factors that Affect Resistance Length of Wire Long wires = high resistance (longer travel) Short Wires = low resistance Thickness of wire (increasing diameter) Thick wire: low resistance (more electrons flow) Narrow wire: high resistance

Factors that Affect Resistance Temperature High temperature: high resistance (electrons collide more) Low temperatures: low resistance Composition (make-up) Conductors: low resistance Insulators: high resistance Resistivity: how strongly a material opposes the flow of electric current

Ohm’s Law Voltage in a circuit equals the product of the current and the resistance Increasing the voltage will increase current Increasing the resistance will decrease the current

Voltage = Current * Resistance Ohm’s Law Formula Voltage = Current * Resistance V=I * R V=Voltage (V) I=Current (A) R=Resistance (Ω)

Ohm’s Law Practice A wire carries 25 amps of current and encounters a resistance of 10 ohms. How much voltage is being supplied to the wire? A 300-V battery is attached to a wire that has 100-A of current. What is the resistance of the wire?

Electrical Power The rate at which electrical energy is converted to another form of energy Ex: hair driers turn electrical energy into thermal energy

Electrical Power Formula Electrical Power = Current * Voltage P = I * V P= electrical power (W) I= current (A) V= voltage (V)

Electrical Power Practice How much power is there when a 20-A current in a light bulb has a voltage of 10-V? A 90-W light bulb has a current of 45-A. What is the voltage in the system?

Circuit A complete path through which charge can flow Uses circuit diagrams to understand the path Symbols represents parts of a circuits Four types Open Closed Series Parallel

Circuit Parts and their Symbols Light Bulb (Resistance) Switch Battery/Power Source WIRE Current Flow

Open vs Closed Circuits Open Circuits A circuit in which a switch is involved Switches can stop the flow of electrons Closed Circuits No switch is in the circuit Electrons flow automatically

Series Circuits Charge has only one, single path through which it can flow If one light bulb goes out, all bulbs go out More bulbs on the circuit means more resistance, decreasing current and bulbs are dimmer

Parallel Circuit Circuit with multiple pathways that electrons can flow If a light bulb goes out in a branch, the other light bulbs will stay on Voltage is the same in each branch, so current flows through the branches with lower resistance

Practice

Drawing Diagrams Practice A closed, parallel circuit with three branches. One bulb on each branch. An open, series circuit with 4 light bulbs.

Drawing Diagrams Practice An open, parallel circuit that has three branches. On the first and third branch has two light bulbs. The second branch has one light bulb. Lastly, there is a light bulb on the main wire.

Magnetic Force The force of attraction or repulsion between two objects

Magnetic Poles North Pole & South Pole Magnetic forces goes from the North Pole to the South Pole Forces are strongest at the poles

Magnetic Field Surrounds a magnet that exerts a force on other magnet and objects made of magnetic materials

Attraction & Repulsion Opposite poles attract or come together North & South Poles Repulsion Like poles repel or push away North Pole and North Pole South Pole and South Pole

Breaking a Magnet If you split a magnet into two equal parts, you form two smaller and equal magnets

Magnetic Domains A group of atoms with aligned magnetic poles in the same direction This can be used to make materials magnets.

Magnetic Induction The process by which materials are made into magnets Done by aligning magnetic poles/domains How? Stroke materials in the same direction with a strong magnet

Electromagnetic Is a solenoid with a ferromagnetic core (iron nail) Materials needed: Nail Wire Battery

Solenoid A coil of current carrying wire that produces a magnetic field The loops of wire with electricity Acts like a bar magnet

Strength of Electromagnetic Increasing current will increase the strength More turns of the wire will increase the strength Use an iron core

Practical Uses of Electromagnetics Electric Motors Created by Oersted Uses electromagnetic to turn an axis Converts electrical energy into mechanical energy

Practical Uses of Electromagnetics Electric Generators Created by Faraday Uses electromagnetic induction Changing magnetic field to create current Converts mechanical energy to electrical energy

Practical Uses of Electromagnetics Transformers A device that increases or decreases voltage of an alternating current Has primary and secondary coils Two Types Step-up: Increase voltage Step-down: Decrease voltage Ex: telephones, electricity supply industries

Practical Uses of Electromagnetics Speakers Solenoid placed around one pole of a permanent magnet Current changes direction to increase or decrease sound