Physics 117 Lecture 1 Electronics for Physics Measurement Winter 2016 Prof Pietro Musumeci Your TA assistant Alexandra Latshaw Kacper Checinski About the class Goals of class Laboratory Knudsen A 137 You a partner per lab station Lab time Expect 7 hours per lab One official 4 hour period with TA prof two such sessions One extra slot with prof Tue 3 4pm Any time you want lab access code 8954 About the Class Lecture Mondays Lab write ups from previous week due at start of next lab TA ie that will be different for the two sections Midterm some lab like lecture like questions During week 6 material weeks 1 4 Practical Final 3 hour exam during finals week questions are circuits to build About the Class We will rotate lab partners So you don t get into a rut e g where one person runs the scope the other grabs the parts Share knowledge tricks Extra Lab time Best if you can avoid other formal lab time W 3 7pm R 3 7pm we have an extra station About the class The Winter Monday challenge No class Jan 18th MLK Feb 1st IFEXS Feb 22nd President s day Make up classes on Fri afternoon before Classroom TBA Circuits in Physics 1B Voltage V Recall V is always defined between two points Physics 1B 5V I R V N C m Joules Coulomb work per charge Example If you move 2 C across 5V Energy 10 J Current A Recall j C s m2 I C s Let the cross section be of the whole wire I is the charge per second flowing through cross section of wire Circuit Diagrams This class Real World Physics 1B 5V 5V I R I R ground Voltage is only defined between two points We will often talk about voltage at a point We really mean between it and ground Ohm s law For a large variety of materials V RI Resistors E j Question How is different than R Kirchoff s laws Sum of voltage around a loop is zero Algebraic sum of currents in and out of a node is zero V 0 0 Resistors in series and in parallel V V Itot I1 I2 I1 R1 Vtot V1 V2 Rtot R1 R2 I2 I1 R1 I2 R2 R2 Vtot V1 V2 Itot I1 I2 1 Rtot 1 R1 1 R2 Important cases and approximations V V V R R R 10R R 10R Rtot R 2 Rtot R Rtot 10R Measuring Devices Basic units A ammeter V voltmeter Question In ideal case what is resistance sometimes we say impedance of each Questions 1 Use these devices to measure the voltage drop and current in the resistor R 2 You are in a lab and only have an ammeter resistors and wires Design a voltmeter 3 You are in a lab and only have a voltmeter resistors and wires Design an ammeter YOUR lab bench multimeter as ammeter as voltmeter banana plug Notice use of red and black wires banana jack multimeter V What are these And Or use a DVM your choice Actually these are DMM but are often called DVM in the field LC meter C meter Your Function Generator old School prototyping Breadboard Your breadboard busbars voltages common signals Your Computer brand new At every lab bench available to write as you go can make plots with Excel Handy for looking up specs of devices we will be using on the internet Your Oscilloscope BNC connector Bayonet Neill Concelman Lab has bananato BNC adapters Input impedance 1 M only so harder to break than 50 Question Why is that Your Power Supply If you ever want 2 amps these old ones are below the shelf Feel free to use if necessary Your books YOUR lab book required Hayes and Horowitz Student manual to the Art of Electronics ISBN 0 521 37709 9 You can buy this used for about 25 on Amazon There is one extra copy in lab but you will want your own to bring home Recommended books available in lab Robert Paynter Introductory Electronic Devices and Circuits It s like a Physics 1 series view of electronics Very well done ISBN 978 0131716414 Horowitz and Hill The Art of Electronics 2nd edition The Bible Lots of information and encyclopedic knowledge Not the best explanations ISBN 0 521 37095 7 Robert Simpson Introductory Electronics for Scientists and Engineers Written for physicists Very real explanations and at level of a physics major ISBN 0 205 08377 3 Reading Resistors Example 11k Notes not sci notation sometimes 2 sometimes 3 significant figures Voltage Divider 4V Question What is voltage at Vout what do we mean by voltage at a point R1 10k Vout R2 30k Doing calc s the electronics way What is current 3V 1 5k What is time constant 2 F 10 k Voltage Divider with Load A load is anything that will draw current when a voltage is applied across it Resistor is a good example 4V R1 10k What happens qualitatively to Vout if there is a load on the output Vout R2 30k RLOAD Quantitative Analysis How the effect of a second stage circuit effects the first stage is a critical component of this course electronics in general Concepts next time output impedance input impedance Th venin Theorem Any network of resistors voltage sources and current sources is equivalent to a single ideal voltage source in series with a resistor black box A B A B Need to calculate VTH and RTH Black Box Vout ideal voltage source VTH RTH This should remind you of real vs ideal batteries from Physics 1B Ideal Battery 4V 1k V Voltmeter reads 4V V Voltmeter reads 4V 4V 1 This should remind you of real vs ideal batteries from Physics 1B Real Battery 1 4V 1k V Voltmeter reads 4V 3 996V V Voltmeter reads 2V 1 4V 1 Calculate VTH for voltage divider Vin RTH Vopen circuit no current EXPLAIN VTH Vopen circuit VTH Th venin Rules for voltage divider short circuit to ground RTH VTH Explain RTH VTH ISS A Example calculating VTH RTH 1 VTH open circuit no load voltage 2 Find the short circuit current ISS 3 RTH VTH ISS 4V Our voltage divider example Slide 2 1 VTH 3 0 V 2 V I R 4 0V ISS 10 k ISS 0 4 mA 3 RTH VTH ISS 3 0V 0 4mA 7 5 k R1 10k Vout R2 30k Black Box VTH 3 0V Vout RTH 7 5 k RTH is often called Output Impedance Input Impedance For a given VIN a circuit draws IIN RIN VIN IIN The more current an element draws for a given voltage the lower its input impedance The less current an element draws for a given voltage the higher its input impedance Question Do you want your voltmeter to have a high input impedance or low input impedance Vout VTH 3 0V RTH 7 5k Rload Notice behavior Vout 3 0V when high resistance load Vout goes down as load resistance gets smaller RTH is often called the output impedance of a circuit looking backward …