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Orientation for Physics Lab for Engineers 2304 193, 194 and 169 Email: [email protected] This document is available at Physicslab Homepage http://www.physicslab.sc.chula.ac.th 1 A Glimpse of Physics Experiments Why experiment is important? Experiment is used to identify a value of unknown quantity from the known physics formula, i.e. to find a gravitational constant (g) from a swing of pendulum, using an equation T 2 l g Results from experiments can help formulate the relationship between two quantities, despite precise formula is yet to be identified. It is well accepated that any new theory/hypothesis must be physically verified by a real observation (experiment). Sometimes, an advanced experiment can lead to a new physics phenomenon. 3 Goals of the physics lab courses Measurement skills that minimize errors - discrepancy between result and theoretical values. The use of instruments - understand how it works and basic operation. Data recording with appropriate accuracy and precision. Error analysis of the results. Data analysis by statistical and graphical methods. Gaining physics concept 4 Important Accessories Pen Pencil Rubber/Eraser Transparent Ruler Scientific Calculator etc. List of Exp.No st 1 Year Physics Experiments Experiment 1 Measurement & Uncertainties 2 Simple Pendulum, Linear Graph and Statistical Analysis 4 Simple Harmonic & Hooke's Law 5 Moment of Inertia 6 Central Force 7 PostTest Yes EN IND ENG G19 A16 193 4 9 1 1 1 No 2 2 2 No 4 4 4 5 5 5 No 6 6 6 Rotational Motion No 7 7 7 9 Standing Waves No 9 9 9 10 Viscosity of Fluid No 10 10 10 21 Heat Capacity No 21 21 21 22 Sound Waves (Beats & Fourier Analysis) No 22 22 22 Yes List of Exp.N o st 1 Year Physics Experiments Experiment 11 Electrical Measurement 13 Ammeter & Voltmeter 14 Basic Oscilloscope Operation 15 Alternating Current 17 Lenses and Spherical Mirrors 18 Polarization of Light 19 Interference and Diffraction of Light 31 Electrical Field Lines nd Equipotential Lines 33 Transistor and Semiconductor Devices 35 Electromagnetic Induction PostTest Yes EN EN G19 G19 3 4 IND A16 9 11 11 11 No 13 13 13 No 14 14 14 Yes 15 15 15 Yes 17 17 17 18 18 18 Yes 19 19 19 Yes 31 31 31 No 33 33 33 No 35 35 35 No Lab Schedule Lab. Schedule 2304194 Wednesday, 9:00 - 12.00 AM Week Orientation 1st **NO LAB** 2nd 3rd 4th 5th 6th **NO LAB** 7th 8th 9th 10th Review Lab. **NO LAB** Make-up Lab Date 7-Jan-15 14-Jan-2015 21-Jan-2015 28-Jan-2015 4-Feb-2015 11-Feb-2015 18-Feb-2018 25-Feb-2015 4-Mar-2015 11-Mar-2015 18-Mar-2015 25-Mar-2015 1-Apr-2015 8-Apr-2015 15-Apr-2015 22-Apr-2015 Lab. Schedule 2304169 Friday, 9:00 - 12.00 AM Week Orientation **NO LAB** **NO LAB** 1st 2nd 3rd 4th 5th **NO LAB** 6th 7th 8th 9th 10th Review Lab. Make-up Lab Date 9-Jan-15 16-Jan-15 23-Jan-15 30-Jan-2015 6-Feb-2015 13-Feb-2015 20-Feb-2015 27-Feb-2015 06-Mar-2015 13-Mar-2015 20-Mar-2015 27-Mar-2015 03-Apr-2015 10-Apr-15 17-Apr-2015 24-Apr-2015 8 Grading policy Experimental part (10 Labs) 70 points 7 points for each lab. 2 points for general evaluations On time for class Manner in class Behavior in class 5 points for Data sheet Post-Test in class (see course syllabus) Final exam (written) 30 points 9 General rules Be in class no later than 10 minutes, After 20 minutes is considered being late (1 point reduction). After 30 minutes, student is not allowed to enter the lab. Dress properly according to the university code of uniforms. IF NOT, you may be refused to enter the lab or 1-2 point of score will be deduced. No use of mobile phone/Tablet PC/PC in class. Do not leave the laboratory room at any time without notifying an instructor. Stay at your table until the experiment is finished unless necessary. Do not make unnecessary loud noise. No food or drink in the laboratory room. 10 General procedures 2-3 students per group for each experiment. Check your lab schedule and partners at the front of room 505, MHMK Bldg or on the Website http://www.physicslab.sc.chula.ac.th. Sign your name before getting into the lab room and obtain the data sheet. Sign up for other person is considered cheating! All parties involved will get a punishment - maximum of 7 pts score deduction. The issue will also be reported to your course administrator. In some lab, student is required to sign up for checking out an experiment kit. After finishing the lab, all checked-out items must be returned. If damage occurs, student(s) will be held responsible (charge or replacement). Submit your data sheet on time (informed at the briefing). Do not take your data sheet out of the lab room. It is not accepted after the class is already over. 11 A Make-Up Class Policy If you miss more than 2 classes, you have no right to take the final examination (<80% attendance). You are advised to “WITHDRAW” before the final exam, otherwise an F grade will be given. If you miss any class, please contact the laboratory staff within 7 days with supporting documents, i.e. a medical certificate, official letter from a respected organization, etc. sufficiently explaining why you could not attend the class. The laboratory instructor/staff retains the right to accept/reject those documents. Only ONE make-up experiment can be arranged for any student during the MAKE-UP week. Beware that attending a make-up class does not necessarily reduce the number of your absences in normal class. 12 Personnel & Staff Security Issue Threatening or injuring instructors/staffs is a very serious issue. The issue will be reported to your course administrator and your family. If seriously, punishment will be executed to the maximum extend by university law and criminal law. 13 Comments Form The comment form is available at every lab room, in a box near the entrance door. Student can evaluate or comment on each lab and drop the form into the box nearby. Not necessarily do or return the form during the lab. You can take the form home and drop it at any lab room next time you come to the lab. Your comments are important and useful to make things better! 14 Error analysis and graph Note that the following details appear in Lab books 2304193 and 2304169 Only • • • • • Types of errors Preliminary description of error analysis Propagation of uncertainties How to report and use uncertainties? Straight line 15 Types of errors • Personal error – Individual mistake - must be avoided or minimized. • Systematic error - measurement tool – Calibration should be done. • Statistical error – Random uncertainty from repeated measurement. 16 Preliminary Description of Error Analysis use error in the sense of “uncertainty”: error do not involve ‘mistake’ in a scientific measurement. no scientific measurement can yield exact value. knowing the uncertainty is important! 17 Example: Is the crown made of gold? Perform the density measurement of the crown gold = 15.5 g/cm3 and Measurement report alloy = 13.8 g/cm3 Student A Best estimate of crown 15 g/cm3 Uncertianty() for crown 1.5 g/cm3 alloy 13.8 g/cm3 Student B 13.9 g/cm3 0.2 g/cm3 gold 15.5 g/cm3 density 13.5 16.5 13.7 14.1 Student A Student B 18 Estimating uncertainties when reading scales No specific criteria, up to your confidence. But try not to underestimate or overestimate it. reading on a meter 2.2 ± 0.2 (definitely between 2.0 and 2.4) reading on a ruler 2.77 ± 0.03 cm (definitely between 2.74 and 2.80 cm) 19 Estimating uncertainties in repeatable measurements Same quantities obtained from several readings/ repeating. Best estimate = average value Standard deviation () is 68% confidence limit. N 2 ( x x ) i i 1 N 1 68 of 100 readings will fall within x S.D. and x S.D. Uncertainty of the mean () is N 20 Propagation of uncertainties calculation of quantities consisting of uncertainties: A =a a, B=b b, C=c c 1. sums or differences (maximum uncertainty) A+B-C = (a+b-c) (a+b+c) example: M1 = 55 1 kg and M2 = 380 30 kg MT = M1+M2 = (55+380) MT kg MT = 1+30 = 31 kg 21 Propagation of uncertainties 2. products or quotients (maximum uncertainty) A x B = (a x b) AB A/B = (a/b) A/B AB ab a b A/ B a a/b b a b a b example: W = 1.3 0.1 cm and L= 2.1 0.3 cm area = WL = (1.3x2.1) WL cm2 = 2.73 WL cm2 WL / 2.73 = (0.1/1.3) + (0.3/2.1) = 0.2198 WL = 2.73 x 0.2198 = 0.600054 0.6 cm2 22 Propagation of uncertainties Combined statistical uncertainties A =a a, B=b b, C=c c 1. sums or differences X = A + B – C = x x 2 2 2 x = a + b – c, x (a ) (b) (c) 2. products or quotients Y = A B / C = y y y = ab / c, y y a b c a b c 2 2 2 23 Propagation of uncertainties more example: q = ? max. uncertainty: ab q y z q |q| a |a| b |b| y | y| z |z| stat. uncertainty: q 2 a b y z q a b y z 2 2 2 Read more in your lab manual ... 24 How to report and use uncertainties? • Always include the units. (measured value of x) = best estimate uncertainty • Rule for stating uncertainties In an introductory laboratory, experimental uncertainty usually be rounded to one significant figure. example: (measured of g) = 9.82 0.02385 m/s2 should be reported as 9.82 0.02 m/s2 or the mass of 5.24 0.4637 g should be reported as 5.2 0.5 g 25 How to report and use uncertainties? • Rule for stating answers The last significant figure in any stated answer should usually be of the same order of magnitude (in the same decimal position) as the uncertainty. Example: best estimate uncertainty stated answer 92.855 0.05 92.86 0.05 92.855 0.5 92.9 0.5 92.855 5 93 5 26 How to report and use uncertainties? • Using scientific notation for a very large or small value. Example: 1. (measured charge) = 1.59x10-19 5x10-21 C should report as (1.59 0.05 ) x 10-19 C 2. 1,857,000 40,000 1.857 x 106 4 x 104 ( 1.86 0.04 ) x 106 27 Straight line • Linear equation: y = m x + c m is slope and c is y-intercept. They can be evaluated using either graphical analysis or statistical analysis (lab 2). • Usually, data are plotted to see if they satisfy linear equation (straight line). 28 Best fit for a straight line 30.00 25.00 y 20.00 15.00 10.00 di • Number of data points above the line is about the same to that of under the line. 5.00 • Summation of the 0 10 20 30 40 50 60 vertical distances for x each data point to di2 = (yline- ydata)2 is minimum the line is minimum. 0.00 29 Best fit :practical approach • Number of data points above the line is about the same to that of under the line. • Summation of the vertical distances for each data point to the line is minimum. 30 Exercise • Let 1. What is the unit of z? 2. Write down the formula for the maximum uncertainty z. 3. Report z and z 31 Homework • Read the Introduction part in the lab book (not included in 2304194 lab book). • Bring your calculator and learn how to use it to get the mean and standard deviation of a set of data. 32 www.physicslab.sc.chula.ac.th