University Physics II Lab
University Physics II Lab PHYS 261
Popular in Course
Popular in Physics 2
This 6 page Class Notes was uploaded by Sonny Breitenberg on Monday September 28, 2015. The Class Notes belongs to PHYS 261 at George Mason University taught by Staff in Fall. Since its upload, it has received 33 views. For similar materials see /class/215189/phys-261-george-mason-university in Physics 2 at George Mason University.
Reviews for University Physics II Lab
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 09/28/15
Multimeters and Ohm s Law Theory Today39s lab will look at some basics of electricity and how these relate to simple circuit diagrams Three basic terms are important to a study of electricity They are basic to understanding Ohm39s Law which states Voltage 7 constant Current This constant is defined as the resistance of an object Its unit is the ohm or Q 39 Current is de ned as the ow of electrical charge from one place to another It is the amount of charge that passes a given point in a unit of time and is measured in units of amperes amps coulsec Voltage is a measure of potential potential difference between two points in a conductor It is a measure of the amount of energy it takes to move charge from the one point to the other It is measured in units called m volt Joulecoulomb Resistance is a measure of the amount of impedance a material presents to the flow of electricity George Ohm showed it is the ratio of the voltage across a material to the current that can then ow through it It depends upon the properties of the conducting material its nature and dimensions but for metallic conductors is usually a constant at constant temperature It is measured in units of ohms where one ohm is defined as 1 volt l ampere We will demonstrate Ohm39s Law for several combinations of resistors verifying the general rule R By K I l l where RM 2R1 for res1stors comb1ned 1n series and 7 2 7 for res1stors Rm R1 combined in parallel Apparatus Three new items that this lab uses are resistors multimeters and power supplies Resistors are used in large numbers in electronic equipment to control the ow of electrical current Physically they are manufactured in a number of styles which feature either high power capacity high precision or low cost This lab will use the most common low cost carbon composite style shown in Figure 31 The physical size determines the power rating P IV 12R V2R The 4 watt W size is about 7mm long by 2 to 3mm in diameter while the 2 W 1W and 2W are progressively larger The l4W resistors are designed to handle up to l4W of power before overheating The low voltage in this experiment makes it safe to feel the resistor in use to check if it is overheating If it becomes hot rather than just warm reduce the voltage or choose a larger resistance value resistor A quick calculation will also serve to check the power before the circuit is energized If a resistor should ever become smoking hot discard it since it will probably be damaged Mlle Igd wbr G mire lea Figure 1 Colored bands indicate the resistance of the resistor The resistance value of a resistor is determined during manufacture by the composition ofthe carbon mix it is made from This resistance is marked on the resistor usually by colored bands as shown in Figure 31 As shown the color bands usually butt up against one end of the resistor shell To read these begin with the band closest that end and decode it and the second band using the following table Table 31 Color Code Resistor Bands 0 black 5 green 1 brown 6 blue 2 red 7 violel 3 orange 8 gray 4 yellow 9 while The third band when similarly decoded is the power of ten of the multiplier For example a resistor marked brown black red should have a resistance of 10 x 102 which equals 10009 or 1 k9 Note that there is no decimal point between the l and 0 The fourth band marks the precision brown or no mark is i 20 silver is i 10 gold is i 5 and indicates how much the actual resistance can differ from that indicated by the colored bands A fifth band sometimes indicates reliability Commercial resistors are designed to have an almost constant resistance over the range of currents and voltages within the power rating Thus a current versus voltage plot will be a straight line within parts per rm an OLhzx umees are m 5a uneu such ashght bums muues a LED s whmh have re ssunee s whnch vary wah euuem mu vunsge The Mummem Inms labuumxyyauwxll make use uf ammumetex Exacth mu Shawn m we gure m we gee m measure elecmcal currentthaty e pecttabeabautl yuuwu seHhe uysmuhmmeww a nwahm39heAxe s m Lhatyau expect u cuxentthat xsless39hAanA Theresultafthe asurementxsshwwnm39h us ay l un e spluymdlcales39hat e quann ys wmsmA andnalA mhe actual cuxemxsgulexthanl mA menme met1 mu displayOL muneuung un awrlaad a mu men me as use me range m 2 mA m muex m get u reading When we sums hxs sem 2 mA yauwx muse um yaulase me sxgn cant gt uf accuracy m we reading he w chrecewecablesa encaedpzabesthat e cannecudtathz cucu Nlmeasmementsmakeuse um COMcammm mpuz Fm vunuge frequency Andreastance measurements me le mastplug labelestQ 5 used slangw hCOM Faxlww curemsLhepluglabeledmAxsused uungmmcom Fm emems up w m A me 1 A plugxs useu slang wnhCOM Just below the display are two buttons The function of the ONOFF and DCAC are very important but selfexplanatory The accuracy of the multimeter is specified for each type of measurement in the sections that follow This accuracy is expressed as a percentage plus a factor related to the number of digits in the display For example DC voltages have an uncertainty of 05 plus one least significant digit In the 2 V range the least significant digit is i 0001 V So if you were measuring a voltage of 10 V the 05 would give an uncertainty of 0005 V and you would add the least significant digit to give an overall uncertainty ofi 0006 V Voltage Measurements To make a voltage measurement select AC or DC turn the rotary switch to the V area and select the appropriate range If you are unsure of the range set the rotary switch to the highest range and then lower it later Insert the probes into the V 9 and COM plugs and then connect them to the appropriate points in the circuit If you are making a DC measurement then the V 9 probe should be connected to the most positive voltage and the COM probe should be connected to the most negative If the probes are not connected correctly then the display will indicate a negative voltage but there is no need to switch the connections If you are making an AC voltage measurement the COM probe should be connected to the point closest to ground Electrical Speci cations for voltage measurements DC VOLTS Ranges 200mV 2V 20V 200V Accuracy i 05 l lsd Input Impedance gt 10 M9 AC VOLTS Ranges 2V 20V 200V 750V Accuracy i 10 3 lsd Input Impedance gt 10 M9 lsd least significant digit Current Measurements To make a current measurement select AC or DC and turn the rotary switch to the A area and select the appropriate range If you are unsure of the range set the rotary switch to the highest range and then lower it later Insert the probes into the mA Cx and COM plugs and then connect them to the circuit It is important to note that the current meter must be part of the circuit as shown in Figure 33 which shows a typical use of voltage and current meter If you expect a current in the 10 A range then the 10 A and COM plugs should be used and the rotary switch should be set to the 20m10A position If you are making a DC measurement then the mA Cx probe should be connected to the most positive voltage and the COM probe should be connected to the most negative voltage If the probes are not connected correctly then the display will indicate a negative current but there is no need to switch the connections If you are making an AC voltage measurement the COM probe should be connected to the point closest to ground Electrical Speci cations for current measurements DC Current Ranges ZOuA 200uA 2mA 20mA 200mA 10A i 2 5 1sd Accuracy 20 uA Accuracy 200uA to i 08 l lsd 20mA range Accuracy 200mA to i 12 1 lSd 2A range Accuracy 10A range i 2 5 lsd Input PrOtecnon 2A 250V fuse mA and not lsed A AC Current Ranges 20uA 200uA 2mA 20mA 200mA 10A i 3 7 1sd Accuracy 20 uA i 0 gtxlt Accuracy 200uA 1398 A 3 18d Accuracy i 10 3 lsd 40400Hz 2mA to 20mA range Accuracy i 18 3 lsd 40400Hz 200mA to 2A range Accuracy 10A range i 30 7 lsdquot 40400Hz Input Protection 2A 250V fuse mA not fused A lsd least signi cant digit Resistance Measurements The multimeter can also be use to measure the resistance of a resistor or other circuit component In making resistance measurements the resistor must be completely removed from the circuit The V Q probe should be connected to one end of the resistor and the COM probe should be connected to the other end Turn the rotary switch to the Q area and select the appropriate range ZkQ to ZMQ range Resistance Ranges 2009 2kg 20kg 200kQ 2M9 20MQ 2000MQ Accuracy 2009 i 08 3 lsd Accuracy i 08 l lsd Accuracy 20MQ range i 10 21sd Overload Protection 250 VDC or AC RMS lsd least signi cant digit