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Transcript
EE1010 Laboratory Instruments and Methods Lee Brinton 801-957-4828 James Quebbeman 801-957-4786 Harvey Wilson 801-957-4786 Four Fundamental Forces of Nature Strong Nuclear Force: Binds positively charged protons and neutrons together to form the nucleus – strongest of four forces. Electromagnetic Force: Attraction and repulsion of charged particles. Weak Nuclear Force: Associated with Beta decay, holds an electron and proton together to form neutron in nucleus of atom. Gravitational Force: Attractive force of mass – weakest of the forces. Gravitational Field Directed Towards the Mass A gravitational field has the potential to create a force when another mass is brought into the reach of the field. Force Due to Gravitational Field m F = mg Δw = energy = Fd = mgh Potential = gh Everything Is Made Of Atoms Nucleus Protons Neutron - BIG! 1,000’s of times BIGGER than electrons + + Surrounding the Nucleus - Electrons Teeny, tiny, itsy, bitsy Electrons: Like flies buzzing around a cow! Moooooove, You pesky Flies! Electrical Field Charged Particles Produce Fields Analogous to Gravitation Field of a Mass E - Force Due to Electrical Field d E + Attractive Force Force: F = qE similar to Energy : Δw = Fd = qEd Potential: V = qEd/q = Ed F = mg Δw = mgh mgh/m = gh In Electricity, this last quantity is called Voltage or Electromotive Force For an introduction to Voltage titled “Physics – What is Voltage” go to this web site: http://www.youtube.com/watch?v=wT9AsY79f1k&list=PL752E6CC30238E56A&index=1 Voltage Generation These voltages can be produced (generated) in a number of different methods • Chemically • in a battery (or a potato) • in a solar cell • in a hydrogen fuel cell • Mechanically – Generator turned by a mechanical device like • a steam powered turbine • a hydro powered turbine • a wind mill Regardless of how the voltage is generated, a voltage source has two terminals – one terminal raised to a higher voltage than the other by one of the methods mentioned above. Schematically, voltage sources are represented with one of the following symbols: + + - A DC voltage source symbolic of separated metallic plates in a battery A generic voltage source that can represent either a DC or AC voltage. Potential or Voltage Always Relative to a Reference For example, in a 9 Volt battery, the chemical reactions raise the“+” terminal to a potential 9 volts higher than the negative terminal + 9V - This terminal is 9 V. higher than … this terminal. Reference Voltage The voltage at a point is always measured relative to some other point. In a 9 V battery, the “+” terminal is said to have a voltage that is 9 Volts higher than the “-” terminal. It becomes useful to define one point within the circuit as the reference voltage (call it 0 Volts) and compare the voltage of all other points in the circuit to that. In hand held or battery operated devices, the reference point of the circuit is frequently the negative terminal of the battery. In devices powered by the utility grid, the reference point of the circuit is usually the neutral wire which is usually connected to the earth ground. Modern construction codes direct that this connection to the earth is made by driving a copper rod into the ground. Current – Rate of Flow Water Flows From Higher to Lower Elevation + Gallons per Minute Charged Particles Flow Higher to Lower Voltage Coulombs per Second Amperes Electrons Constrained Within a Conductor With the “+” terminal at a higher voltage than the “-” terminal, a potential exists to force positively charged particles from the higher voltage to the lower voltage. To accomplish this, a charge carrying material known as a conductor must be connected between the terminals to provide a path for the particles to flow. This closed path is referred to as a CIRCUIT. The flow of charged particles is referred to as a CURRENT. + + - A circuit schematic showing a battery (left) connected using conductors (red lines) to a resistor (right) . Historical Note When we talk about current, we refer to it as though “+” charges flow from the “+” terminal to the negative terminal. This is the commonly used convention we use. + + - - In reality, electrons are flowing from the negative terminal to the positive terminal. Another Analogy Pressurized Water in a Closed Pipe Pump infuses energy by raising pressure X Restriction reduces pressure and dissipates energy Battery infuses energy by raising voltage Resistor reduces voltage and dissipates energy Voltage and Elevation (An Analogy) Our understanding of voltage can be enhanced through a comparison to elevations. Elevations are always measured relative to some reference elevation that is considered to have an elevation of 0 feet. Heights above the reference are positive and heights below the reference are considered negative. For example, sea level is frequently considered the reference elevation and assigned an elevation of 0 feet. Other elevations are measured relative to sea level. Highest point on Earth Elevation of Mt. Everest 29,035 ft Elevation of base station 17,600 ft Sea Level = 0 The difference in elevation between the peak and the base camp is hpeak – hbase or 29,035 – 17,600 = 11,435 ft. When referring to the change in elevation, we can either say there is an increase in elevation of 11,435 ft from the base camp to the peak or a drop in elevation of 11,435 ft from the peak to the base. The drop in elevation going from the peak of Everest to the bottom of the Challenger Deep is: hpeak – hdeep or Lowest point on Earth 29,035 – (-36,200) = 65,235 ft. Challenger Deep – Marianas Trench -36,200 ft Voltage and Elevation (An Analogy) 1 kΩ + 1 Volt - 1 Foot + 10 Volts - 10 kΩ 12 V 1 kΩ Circuit schematic 12 Feet 10 Feet + 1 Volt - 1 Foot Elevation chart Schematic and Simulation 1 kΩ + 1 Volt + 10 Volts - 10 kΩ 12 V 1 kΩ + 1 Volt - Simulate using Voltage_Ideal_Simulated.rtf Measuring Voltage Construct the circuit in a simulator Measure and record each voltage in the table below d 1 kΩ 12 V + 1 Volt c 10 kΩ b 1 kΩ + 10 Volts + 1 Volt a VDA VCA VBA VDC VCB VDB Building Circuits – Another View Two Versions of Prototype Boards in Our Lab Protoboard description: http://www.doctronics.co.uk/prototyp.htm#board Resistor description: http://www.youtube.com/watch?v=Gc1wVdbVI0E Schematic and Protoboard + 1 Volt - 1 kΩ 12 V 10 kΩ 1 kΩ + 10 Volts - + 1 Volt - Ohm Meter (verify resistance value) Measure Resistance at One Point Relative to Another. Indicated value should be within 5% of expected value. Volt Meter Measure Voltage at One Point Relative to Another. Value indicated may be slightly different from expected. Measuring Voltage Construct the circuit on a protoboard Make the same measurements that were done in the simulation Compare the ideal values with the simulated and the protoboard values d 1 kΩ 12 V + 1 Volt c 10 kΩ b 1 kΩ + 10 Volts + 1 Volt a VDA VCA VBA VDC VCB VDB