PHYSICS 2DL SPRING 2010 MODERN PHYSICS LABORATORY Monday April 5, - - PowerPoint PPT Presentation

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PHYSICS 2DL SPRING 2010 MODERN PHYSICS LABORATORY Monday April 5, - - PowerPoint PPT Presentation

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PHYSICS 2DL SPRING 2010 MODERN PHYSICS LABORATORY Monday April 5, 2010 Prof. Brian Keating 04/05/2010 2DL Lecture 2 2DL Review of policies from last week Theory of first few experiments continues in lab this week No lecture

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04/05/2010 2DL Lecture 2

PHYSICS 2DL – SPRING 2010

MODERN PHYSICS LABORATORY

Monday April 5, 2010

  • Prof. Brian Keating
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04/05/2010 2DL Lecture 2

2DL

  • Review of policies from last week
  • Theory of first few experiments continues

in lab this week

  • No lecture May 31
  • Error propagation
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04/05/2010 2DL Lecture 2

 Policies 

  • Missed labs CAN’T be copied!
  • Must attend make up lab, take data

YOURSELF, and write up labs. Missing, Copying data and/or reports will result in 0 points for that lab.

  • Need a note from doctor or UCSD official

to be allowed to re-take lab.

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04/05/2010 2DL Lecture 2

Lab Manual Textbook

“Introduction to Error Analysis”, by Taylor No experimental information but good intro on how to handle data once your experiment produces some… Full of Homework problems and helpful examples. $28 used on Amazon Printed out and bound for you. Will be distributed in your lab section next week.

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04/05/2010 2DL Lecture 2

Homework

  • Problems listed on 2DL Spring 2010

syllabus -Website:

  • http://physics.ucsd.edu/students/courses/

spring2010/physics2dl/

  • Website has lecture notes from prev week
  • All HW problems are found in Taylor
  • Hand-in HW to TA in Lab as on schedule,

(changed on syllabus).

  • HW #10 IS due in lab, week of 31 May

(Memorial Day week so no lecture).

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04/05/2010 2DL Lecture 2

Lab Sections (Tuesday/Thursday 12:30p & Wednesday 1p, 3 hours

  • Introduction to the experiments (this week)

in lab.

  • You start doing the labs in week 3 - next

week.

  • Pick your partners THIS WEEK IN LAB.
  • Sign up for your weekly labs THIS WEEK IN

LAB.

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04/05/2010 2DL Lecture 2

Notebooks

  • Few pages of text
  • Include data, plots
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04/05/2010 2DL Lecture 2

Lab Notebooks & Reports

  • See ‘Ace your

Reports’

  • Include data,

plots with labels, sketches, in ink.

  • D. Osheroff, 1972. Winner of 1996 Nobel Prize in

Physics

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04/05/2010 2DL Lecture 2

Errors uncertainties

not mistakes! inevitable and intrinsic part

  • f any measurement

Principal sources of errors in measurements: 1) limitations of measurements tool random errors can be reduced through statistical methods

Scientific Errors

3) imprecise definition of measured quantity 2) limitations of experiment design

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04/05/2010 2DL Lecture 2

Quantifying Errors

  • a. Precision. This is a measure of

repeatability, i.e. the degree of agreement between individual measurements of a set of measurements, all of the same quantity

  • b. Accuracy. This is a measure of

reliability, and is the difference between the True Value of a measured quantity and the Most Probable Value which has been derived from a series of measures.

  • c. Resolution. This is the smallest

interval measurable by an instrument.

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04/05/2010 2DL Lecture 2

Measurements and Errors

Always present, Inevitable! 9999 10000 “true” mileage?

9999 + 1

_

best

estimate uncertainty

9999.7 + 0.1

_

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04/05/2010 2DL Lecture 2

Error Propagation

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04/05/2010 2DL Lecture 2

10-3 m Limitations of measurement tools 10-4 m 10-5 m test masses

5,600 m

laser detector LIGO observatory

10-19 m!

Measure L = L1 + L2 L1 = 1.01, L2 = 1.1, what is L?

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04/05/2010 2DL Lecture 2

Accuracy versus Precision

accurate but imprecise precise but inaccurate

Current [A] Voltage[V] Ohm’s Law: V=IR

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04/05/2010 2DL Lecture 2

Accuracy versus Precision

accurate but imprecise precise but inaccurate … how close to the “true” value … uncertainty Systematic error

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04/05/2010 2DL Lecture 2

Error Propagation

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04/05/2010 2DL Lecture 2

xbest

Error Propagation

xbest - δx xbest + δx

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04/05/2010 2DL Lecture 2

xbest

Error Propagation

xbest - δx xbest + δx

qbest = q(xbest)

q(xbest – δx) q(xbest + δx)

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04/05/2010 2DL Lecture 2

xbest

Error Propagation

xbest - δx xbest + δx

qbest = q(xbest)

q(xbest – δx) q(xbest + δx)

δq = q(xbest+δx) – q(xbest) δq depends on: 1) δx 2) q(x)

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04/05/2010 2DL Lecture 2

Error propagation

δq = q(xbest+δx) – q(x)

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04/05/2010 2DL Lecture 2

Error propagation

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04/05/2010 2DL Lecture 2

Simple Example: Adding Uncertainties

  • Measure Diameter, D = 6.0 ± 0.1 m
  • Radius = R?
  • Circumference = C?
  • C = 18.8 ± 0.3 m
  • R = 3.00 ± 0.05 m

R

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SLIDE 23

04/05/2010 2DL Lecture 2

y3-(A+Bx3) y4-(A+Bx4) true value

LEAST SQUARES FITTING

1.

  • 2. Minimize χ2:

…

  • 3.  A in terms of xj yj ; B in terms of xj yj , …

xj ;yj y = f(x)

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04/05/2010 2DL Lecture 2

Basic Electronics- this week in Lab

  • Play with RLC circuit elements and

Oscilloscopes

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04/05/2010 2DL Lecture 2

Simplest Circuit

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04/05/2010 2DL Lecture 2

Electrons in a Resistor

Lines of Electric Force (-Electric Field) Atoms of Resistor Material (e.g. Carbon) F= ma = qE

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04/05/2010 2DL Lecture 2

Resistor Fabrication

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04/05/2010 2DL Lecture 2

E R

Work done by battery

  • n the charge:

dW = Edq = Eidt E i dt = i2 R dt(~Fd)

Thermal energy at the resistor

E = iR

RLC Circuits: the Loop Rule

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04/05/2010 2DL Lecture 2

More Advanced Circuits

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04/05/2010 2DL Lecture 2

E&M & H2O

  • Example analogies
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04/05/2010 2DL Lecture 2

H2O resistor

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04/05/2010 2DL Lecture 2

E&M & H2O

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04/05/2010 2DL Lecture 2

E&M & H2O

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04/05/2010 2DL Lecture 2

Inductors Capacitor

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04/05/2010 2DL Lecture 2

Inductor Inductor

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04/05/2010 2DL Lecture 2

Inductor Inductor

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04/05/2010 2DL Lecture 2

Inductor Inductor

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04/05/2010 2DL Lecture 2

Inductor Inductor

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04/05/2010 2DL Lecture 2

Oscilloscopes

  • You can determine the time and voltage values of a signal.
  • You can calculate the frequency of an oscillating signal.
  • You can tell if a malfunctioning component is distorting the signal.
  • You can find out how much of a signal is direct current (DC) or alternating current (AC).
  • You can tell how much of the signal is noise and whether the noise is changing with time.
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04/05/2010 2DL Lecture 2

Oscilloscope

J.J.Thomson N.P. physics 1906

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04/05/2010 2DL Lecture 2

Oscilloscope

J.J.Thomson N.P. physics 1906

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04/05/2010 2DL Lecture 2

Oscilloscope

J.J.Thomson N.P. physics 1906

Similar to the TV…

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04/05/2010 2DL Lecture 2

Oscilloscope

trigger Ch 1 Ch2 ext coupling DC AC LF rej HF rej vertical scale

V/div Ch1 Ch2 Ext input Sec/div

horizontal scale

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SLIDE 44

04/05/2010 2DL Lecture 2

Oscilloscope

trigger Ch 1 Ch2 ext coupling DC AC LF rej HF rej

Sec/div

horizontal scale

Ch1 Ch2 Ext input

vertical scale

V/div