Dynamic Electricity All you need to be an inventor is a good imagination and a pile of junk. -Thomas Edison
Review Everything is made of atoms which contain POSITIVE particles called PROTONS and NEGATIVE particles called ELECTRONS. An atom will usually have the same number of positives and negatives this makes the atom NEUTRAL. Electron (-) Proton (+) Neutron
What is Electricity? The energy created by moving electrons (e - )
What is the difference between static electricity and dynamic electricity? Static electricity is stationary or collects on the surface of an object, whereas dynamic electricity is flowing very rapidly through a conductor. The flow of electricity in dynamic electricity has electrical pressure or voltage. Electric charges flow from an area of high voltage to an area of low voltage. Refers to electrical charges in motion Dynamic electricity runs all our electrical appliances AKA current electricity Power stations generate current electricity and send it through power lines to homes, business and industries
Electricity moves similarly to the way a fluid flows
Would This Work?
Would This Work?
Would This Work?
The Central Concept: Closed Circuit
A Basic Circuit All electric circuits have three main parts: 1. A source of energy 2. A closed path 3. A device which uses the energy If ANY part of the circuit is open the device will not work!
Electric Current The movement of charge around a closed circuit
Current Intensity Electric current is given the symbol Current intensity (or current) is the amount of charge flowing per second It is measured in Coulombs per second (C/s) but the unit we commonly use is amperes (A) 1 A = 1 C/s The bigger the current, the more electrons are flowing around the circuit. I
Current Intensity can be calculated using the formula: I = current intensity (A) q = charge (C) t = time (s) q Ex. A car headlight requires a current of 15 A. What is the charge needed for 1 minute? I t 10/26/2014
Current Intensity can be calculated using the formula: I = current intensity (A) q = charge (C) t = time (s) q Ex. When plugged into the wall for 50 seconds, an alarm clock uses a charge of 25 Coulombs. What current was produced? I t 10/26/2014
Current Intensity Current intensity is measured with an ammeter Ammeters must be placed inside the circuits path so that it can measure the number of charges that flows through at that point
Current Flow - Direction When we talk about current flowing we say that current flows out of the positive terminal of the cell and back into the negative terminal determined before the discovery of the electron What do we call this flow? Conventional Current Current Flow Direction
Electron Flow However, the electrons flow from the negative side of the battery to the positive side. These are the particles which are actually moving through the conductor. Electron Flow Direction
Conventional current and Electron flow What charge do electrons have? What do two negative charges do if placed near to each other? Negative They will repel each other. What will a positive and a negative charge do to each other? They will attract each other.
Conventional current and Electron flow When electrons were discovered, physicists worked out what was really happening. Negatively charged electrons are repelled out of the negative terminal of the cell. They then travel round the circuit and are attracted back to the positive terminal. Conventional current electrons Conventional current
Potential Difference = Voltage In a battery, a series of chemical reactions occur The chemical energy of the battery is converted to electrical energy and is carried by the electrons that move round the circuit. It is converted into others forms of energy.
Potential Difference = Voltage The amount of electrical energy the electrons have at any point in a circuit is known as their potential. As they move the electrons transfer energy into other forms. This means at any two points the electron has different amounts of energy. The difference in energy is the potential difference or voltage The voltage/potential difference is a measure of the electrical energy given to one coulomb of charge passing through the battery
Potential Difference = Voltage
Potential Difference = Voltage Another way of looking at it: The voltage is a measure of how big a push the electrons are given as they leave the cell or battery The bigger the voltage, the bigger the push The cell, battery or power supply produces the voltage. Potential difference is measured in volts (V) One volt is equal to the energy of one joule per one coulomb of charge:
Potential difference can be calculated using the formula: V = potential difference (V) E = Energy (J) q = charge (C) E V q Ex. Electrical circuits in houses usually supply a potential difference of 120 V. How much energy is provided by 200 C of charge?
A voltmeter is used to measure potential difference V A voltmeter determines the amount of energy each of the charges transfers to an element in the circuit (such as a light bulb, motor or resistor) Voltmeters are installed across a component (above the element in the circuit you want measured)
Resistance
Resistance Resistors oppose (or resist) the flow of electric current. They have a property called resistance (R) which is measured in ohms (Ω). Some resistors also function to transform energy from one form to another
Resistors used to transfer energy The metal which makes up a light bulb filament or stovetop eye has a high electrical resistance. This causes light and heat to be given off.
Resistance When electrons (current) move through resistors causes a drop in the amount of energy carried by the charges This means that the higher the resistance, the more energy it takes for current to flow. Resistance(R) is measured in ohms (Ω) An ohm is equal to one volt of potential difference per ampere of current
Varying Resistance The opposition to current or resistance of a material (measured in Ω) depends on: a. type of material (the better the conductor, the lower the resistance) b. length of material (the longer the material, the higher the resistance) c. thickness of material (the thinner the material, the higher the resistance) d. temperature of material (the higher the temperature, the higher the resistance)
Ohm s Law Ohm s Law states that, for a given resistance, the potential difference in an electrical circuit is directly proportional to the current intensity. Example: If the current intensity is doubled but resistance stays the same, the potential difference is also doubled Free template from www.brainybetty.com 10/26/2014
Ohm s Law is represented by The following formula: V = potential difference (V) R = resistance (Ω) I= current intensity (A) V R I
Applying Ohm s Law Ex 1: How much potential difference is needed to push 2 A of current through a 30 Ω resistor? V R I
Ex 2: A 110 volt wall outlet supplies power to a strobe light with a resistance of 2200 Ω. How much current is flowing through the strobe light? V R I
Ex 3: A 120-volt power source supplies a lamp with 0.625 A of current. What is the resistance in the lamp? V R I