Conductors And Insulators PDF

Conductors and Insulators Conductors are made of materials that electricity can flow through easily. These materials are made up of atoms whose electrons can move away freely.  Metals in general are the best conductors of electricity. The atoms of metal elements are characterized...

Conductors and Insulators Conductors are made of materials that electricity can flow through easily. These materials are made up of atoms whose electrons can move away freely.  Metals in general are the best conductors of electricity. The atoms of metal elements are characterized by the presence of electrons in the outer shell of an atom that are free to move about. It is these ‘free electrons’ that allow metals to conduct electric current. Many metals like copper, iron, silver etc. are good conductors of electricity.  Silver is the most conductive metal, however it is very expensive and hence is rarely used. All the electric wires are generally made from copper. Some examples of conductors are: COPPER ALUMINUM PLATINUM GOLD SILVER WATER PEOPLE AND ANIMALS TREES Superconductor: A superconductor is a material that is a perfect conductor. Superconductors are usually a mix of two or more metals. Superconductor: However these are not superconductors at room temperature. They show zero resistance to electric flow at very low temperature usually below -200 degrees celsius. Insulators are materials opposite of conductors. The atoms are not easily freed and are stable, preventing or blocking the flow of electricity.  In insulators the outer electrons are tightly held together, which prevents them from moving. When the movement of electrons is restricted, no current can flow through them. Non-metals such as glass, wood, plastic are excellent insulators as they have high resistance to the flow of electric current.  This is true for normal voltage but increase in voltage may conduct some passage for electricity. Insulating materials like plastic, wood etc are used to cover materials that carry electricity. Some examples of insulators are: GLASS PORCELAIM PLASTIC RUBBER Electricity will always take the shortest path to the ground. Your body is 60% water and that makes you a good conductor of electricity. If a power line has fallen on a tree and you touch the tree you become the path or conductor to the ground and could get electrocuted.  It must be noted that all conductive material do not have the same conductivity and similarly not all insulators have the same level of insulation. Conductivity and insulation also depends on physical dimension of the material.  Two wire of same length but with different diameter, the wire with bigger diameter is a better conductor than the wire with lesser diameter. Similarly two wires of same diameter but with different lengths then the wire with shorter length has proved to be a better conductors than the longer wire.  SHORT QUIZ Get 1/4 sheet of paper 1/4 sir? Yes 1/4 1)____ allows most electricity to pass through them. a)Insulators b)Conductors c)Semi-conductors d)None of these 2. ________ move freely in conductors which allow flow of electricity. a. Atoms b. Protons c. Current d. electrons 3. _______ has zero resistance. a)Super-conductors b)Water c)Ice d)Silver 4. Super conductors work only at temperature below ______ o a)-200 F o b) 200 C o c) 200 F o d) -200 C 5. _______ does not allow electricity to pass through them. a)Water b) people c) animals d) Plastic 6. _______ does not allow electricity to pass through them. a)Water b) people c) animals d) Plastic 7. _______ is a perfect conductors. a)insulators b) semiconductors c) Superconductors d) none 8. TRUE or FALSE: Aluminum is cheaper than silver. 9. TRUE or FALSE: Aluminum is a better conductor of electricity compared to copper. 10. TRUE or FALSE: Pure water conducts electricity.  Lesson 4: Parallel and Series Circuits 01 Series Circuit  Series Circuits Only one path for current to flow The current is the same in all parts of the circuit. IT = I1 = I2 = I3… Therefore, the number of coulombs passing through each load is the same. If the circuit is broken at any point, then the current flow stops.  Series Circuits Since the current flows through all loads, electrons lose energy as they pass through each load. The potential difference (voltage) is split between the loads in the circuit. Therefore, VT = V1 + V2 + V3 …  Series Circuit The resistance increases with each load. RT = R1 + R2 + R3 … The power increases with each load PT = P1 + P2 + P3 … 02 Parallel Circuit  Parallel Circuits There is more than one path for the current to flow Current is NOT the same at different points. The current (the electrons) is shared by as many paths as there exist. Current flowing from the energy source equals the sum of all the separate branch currents in the circuits. IT = I1 + I2 + I3 … I, in each path, depends on the size of the resistor. The more resistors, there are in the circuit, the more “pull” for energy and the greater the current.*  Parallel Circuit If any one device is removed, it does not affect the others. Each branch circuit is connected directly across the battery, therefore has the identical potential difference as there is across the battery. VT = V1 = V2 = V3 …  Parallel Circuit Adding resistance in parallel, decreases the total resistance of the circuit. RT = 1/R1 + 1/R2 + 1/R3 … The power is calculated as follows: PT = P1 + P2 + P3 … 03 Electricity in the home Two Types of Current Direct current – electrons always travel in one direction as in batteries and cells. Alternating current – electrons go back and forth rapidly sixty times per second. This allows for efficient distribution of high voltage electricity via transformers that increase (step up) or decrease (step down) the potential difference of power lines as it gets closer to your home or school  Fun Fact Do you know who invented alternating current? Nikola Tesla Electricity in the home If too much current flows through a wire, it overheats which can lead to a fire. Fuses and circuit breakers detect dangerous current overloads. FUSES – a thin wire that melts at a pre-determined current level so as to break the circuit. Must be replaced with a new fuse. CIRCUIT BREAKER – a heat sensitive switch that “trips” off when current overheats the wire. Can be reset by flipping the switch. Electricity in the home In your home, a digital or dial meter reads the electric current used in kilowatt-hours (1 kW h = 1000 watt hours). Measurements WHAT’S A JOULE?? A JOULE (J) is the unit for ENERGY WHAT’S A WATT?? A WATT (W) is the unit for power - a kilowatt (kW) is one thousand watts ( 1.0 kW = 1000 W) POWER POWER MEASURES “HOW FAST” YOU USE ENERGY – THE EQUATION FOR POWER IS Unit of energy THE kWh as a UNIT OF ENERGY ( hint: get “E” by itself in the power equation)  BASIC ELECTRONIC COMPONENTS Creative Tech STE 9 Voltage: Potential refers to the the possibility of doing work. The symbol for potential difference is E (for electromotive force) The practical unit of potential difference is the volt (V) 1 volt is a measure of the amount of work required to move 1C of charge Current: When a charge is forced to move because of a potential difference (voltage) current is produced. In conductors - free electrons can be forced to move with relative ease, since they require little work to be moved. So current is charge in motion. The more electrons in motion the greater the current.  Amperes: Current indicates the intensity of the electricity in motion. The symbol for current is I (for intensity) and is measured in amperes. The definition of current is: I = Q/T Where I is current in amperes, Q is charge in coulombs, and T is time in seconds. Closed Circuits: In applications requiring the use of current, electrical components are arranged in the form of a circuit. A circuit is defined as a path for current flow. Open circuit : current can only exist when there is conduvtive path. In the circuit I= 0, since there is no conductor between points a and b. we reffered to this as an open circuit. Direction of Electron Flow The direction of electron flow in our circuit is from the negative side of the battery, through the load resistance, back to the positive side of the battery. Direction of conventional current The direction of conventional current in our circuit is from the positive side of the battery, through the load resistance, back to the negativeside of the battery. Direct Current: Circuits that are powered by battery sources are termed direct current circuits. It is the flow of charges in just one direction Alternating Current: An alternating voltage source periodically alternates or reverses in polarity. The resulting current, therefore, periodically reverses in direction.  Resistance: Opposition to the flow of current is termed resistance. The fact that a wire can become hot from the flow of current is evidence of resistance. Conductors have very little resistance. Insulators have large amounts of resistance. Resistors A resistor impedes the flow of electricity through a circuit. Resistors have a set value. Since voltage, current and resistance are related through Ohm’s law, resistors are a good way to control voltage and current in your circuit. 10 More on resistors Resistor color codes 1st band = 1st number 2 nd band = 2 nd number 3rd band = # of zeros / multiplier 4 th band = tolerance 11 Color code 12 Units Knowing your units is important! Kilo and Mega are common in resistors Milli, micro, nano and pico can be used in other components K (kilo) =1,000 M (mega) = 1,000,000 M (milli) = 1/1,000 u (micro) = 1/1,000,000 n (nano) = 1/1,000,000,000 (one trillionth) p (pico) = 1/ 1,000,000,000,000 (one quadrillionth) 13 Ohm’s Law The amount of current in a circuit is dependent on its resistance and the applied voltage. Specifically I = V/R If you know any two of the factors V, I, and R you can calculate the third. Current I = V/R Voltage V = IR Resistance R = V/I Power: The unit of electrical power is the watt. Power is how much work is done over time. One watt of power is equal to the work done in one second by one volt moving one coulomb of charge. Since one coulomb a second is an ampere: Power in watts = volts x amperes P=VxI P = I² x R P = V² / R Capacitors A capacitor stores electrical energy. Capacitance is measured in Farads. The small capacitors usually used in electronics are often measured in microfarads and nanofarads. Some capacitors are polarized. Note the different length terminals on one of the capacitors. 16 Polarity of capacitors The shorter terminal goes on the negative side (cathode). 17 Diode A diode is a one way valve (or gate) for electricity. It is a component with an asymmetrical transfer characteristic. A diode has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other direction. Diodes will protect your electronics. 18 Diode circuit protection In an electronic circuit, if the polarity is wrong, you can fry your components. Diodes have a bar on the cathode (negative) side. 19 Light emitting diode (LED) A light emitting diode (LED) is a semiconductor light source. When electricity is passing through the diode, it emits light. 20 Variable resistor / Potentiometer A potentiometer is a variable resistor. As you manually turn a dial, the resistance changes. 21 Transistors A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. This is our electronic switch! 22 How a transistor works Avoltage or current applied to one pair of the transistor’s terminals changes the current through another pair of terminals. A transistor is composed of semiconductor material with at least three terminals for connection to an external circuit. Transistors have 3pins. For these transistors: Collector Emitter Base 23 Terminology BJT versus FET Bipolar junction transistor. Useful as amplifiers. Collector, Emitter, Base Field-effect transistor. Useful as motor drivers. Source, Drain, Gate MOSFET: Metal-oxide-semiconductor FET NPN (N-channel FET) versus PNP (P-channel FET) NPN versus PNP is how the semiconductors are layered. NPN: Not pointing in PNP: Pointing in permanently 24 Schematic symbols BJTPNP BJTNPN P-channel FET N-channel FET 17 Integrated circuit An integrated circuit (IC) is a set of transistors that is the controller or ‘brain’ of an electronic circuit. An input is received, an output is sent out. Modern microprocessor ICs can have billions of transistors per square inch! 26  Printed Circuit Board Components are attached to a printed circuit board. The ‘front’ side of the board will have printed component information, such as resistor # and resistance, diode type and polarity, etc. Holes go all the way through the board from one side to the other. Through- hole soldering is needed to connect components to the board. 27  Back of Circuit Board The ‘back’ side of the board will have lines indicating connections between components. The lines on the back are similar to wires. Thicker lines denote more current (electrons) moving through. Components connect the lines. 28