Physics 25 - Spring 2026

Announcements:

• 23 March: If you send email to the instructor, please start the subject line with [Phys 25].  Otherwise your mail is likely to be lost in the daily deluge of emails.
• 9 April: Sorry for the late notice.  TA's office hours cancelled today. Email the TA for a zoom appointment Friday morning if you need help.
• 13 April: The lecture of Wednesday April 22 is cancelled.  Here is a doodle poll for a makeup lecture.
• 24 April: The makeup lecture will be on Monday April 27, 6 pm in Chem 1179.   There will also be a zoom option, the link was sent by email.  There will also be a review session for the midterm on Saturday May 2nd at 7 pm in Broida 1640.  (Note: the email that was sent out had two typos.  It said that the makeup lecture was on Friday April 27 and the review session was on Sunday May 2nd).
• 26 April: Midterm information can be found here
• 10 May: Midterm information page (link on line above) updated with solutions and score distribution.
• 28 May: Information on the final can be found here
  

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Instructor:	Claudio Campagnari
Email:	claudio@physics.ucsb.edu
Office:	Broida 5125.  Phone (805) 893-8802.
Office hours:	Wednesday 2:30-3:30, or by appointment, or whenever you can find me
Teaching Assistant	Dani Guillen
Email:	deg@ucsb.edu
Office hours:	Monday, Wednesday, Thursday 11:00-12:00 in the PSR

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Course Description:

Special Relativity.  Introduction to quantum physics: Black body radiation, photoelectric effect, particles as waves, Schrodinger equation.
Beginning atomic and nuclear  physics.

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Textbooks:

For Special Relativity: An Introduction to Mechanics, 2nd edition, Kleppner and Kolenkow.
For everything else: Modern Physics for Scientists and Engineers, 2nd edition, Taylor, Zafiratos, Dubson
I assume you already have a copy (digital or otherwise) of the K&K book from Physics 21. 
The book by Taylor et al, also cover Special Relativity.

From time to time I will also post lecture notes on this page (not always, but when my lectures depart from the books' approach).

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Additional Material

• April 7:  The discussion of the twin paradox in the K&K book is not very good.  One does not need to appeal to General Relativity.  Here are some of my handwritten notes, which refer to this youtube video as well.
• April 13: I asked Claude AI to turn my scribbled notes into something more legible.  Here it is (same content as the handwritten notes..not all the sketches came out perfectly, but good)
  
• April 8: Do neutrinos travel faster than light?  Not really.  The time difference offset that they first measured between the v=c and the v>c hypothesis was about 60 nsec.  In 60 nsec, light travels about 60 feet (~ 18 meters....1 ns/foot is a useful number to remember for c).  Note that the experiment was able to control the distance between where the neutrinos were produced at CERN in Geneva, Switzerland and the Gran Sasso Laboratory in central Italy to an accuracy of 20 cm out of a distance of more than 700 km.  The clocks at CERN and at Gran Sasso were synchronized at the nsec level.
• April 9: Some notes about four-vectors.
• April 15: More notes about four-vectors
• April 27: 
  
• Invariant mass: a tool to discover new particles.
• Natural Units: my lecture notes and a longer writeup from MIT
• A very brief introduction to covariant and contravariant notation
• May 4: Rutherford scattering notes
• May 9: A note on probability distribution functions and another one on why sometime it makes more sense to plot/express things in terms of the cosine of the angle as opposed to the angle itself.
• May 13: Some slides on "modern" versions of Rutherford-like experiments.
• May 20:
  
• ''Derivation" of Schroedinger equation.
  
• Slides on wavepackets.
• More on group velocity for QM waves, a bit beyond what is on the slides.
• May 27:
• QM of Simple Harmonic Oscillator
• Spherical harmonics from Wikipedia
• Here are the equations
• This page has nice pictures
• June 1:  Radial wavefunctions of the H atom equations and pictures.
• June 3: g-2 slides
  

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Discussion Sections

The problems for the discussion sections, curated by the TA, can be found here.

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Homework:

The only way to really verify that you have absorbed the material and, last but not least, to do well on the exams, is to do problems. 
This is the main reason why I will assign weekly a carefully selected list of problems for you to do (aka homework).
However: Homework will not be collected, will not be graded, and will not count towards your final grade.
The main reason for this is that with all the tools at your disposal (solved problems that you can find on the web, chatgpt, help from your friends, the TA, the instructor...) there is little value in assigning a score to the homeworks.
The assignments will have a "virtual" due date as an incentive for you to keep up with the material.  I will also post my solutions to the homework after the virtual due date.  I encourage you to look at my solutions and compare them with yours, in other words "grade your own work".  I suspect that this has more useful than to wait for the TA/grader to return your homework.

Homework Number	Due date	Problems	Solutions
1	10 April	here	here
2	17 April	here	here
3	24 April	here	here
4	1 May	here	here
5	8 May	Nothing
6	18 May	here Also: scans from TZD	here
7	29 May	here Also: scans from TZD	here
8	5 June	here Also: scans from TZD	here

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Exams:

There will be one midterm and one final.  
The midterm will be on Monday, May 4th during normal class time.
The final will be Wednesday, June 10, 8:00-11:00 am.

The final grade for this class will be calculated from a curve based on your scores on th, Midterm (40%), and the Final (60%).
If you miss the midterm for a good reason (eg: illness), your letter grade will be calculated based on the final only.
If you miss the final you will be given an Incomplete.  You will take the Physics 25 final the next time that the class is being offered.

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Tentative Schedule:

Week of March 30	K&K Chapter 12.1 12.2  12.3   12.4.2  12.5  12.7 (started)
Week of Apr 6	12.7 (finished)  12.6 12.8 12.9 14.1 14.2 14.4 14.5.1.  Also, see Some notes about four-vectors
Week of Apr 13	K&K Chapter 12.10 12.11 13.1 13.2 Also, see More notes about four-vectors (will finish these next week)
Week of Apr 20	K&K Chapter 13.3 13.4 13.5,  finish 14
Week of Apr 27	K&K 14, Natural Units, covariant/contravariant (see additional material)  TZD: 3.11 3.12 (Rutherford scattering...but see additional material on that)
Week of May 4	Midterm + Finish Rutherford scattering
Week of May 12	One class missed because of illness of instructor Black-body radiation, Phototelectric effect, Started Compton scattering  TZD 4.2 4.3 4.6
Week of May 19	Finished Compton scattering De Broglie hypothesis, Bohr Atom,  TZD 5.1 5.2 5.3 5.4 5.5 5.6 5.7 6.1 6.2 7.7 Schroedinger Equation:  See my lecture notes (TZD 7.11, sort of) Wavepackets: See my slides.  Also, notes on group velocity (if you forgot/did not know)  TZD 6.7 6.8 6.10
Week of May 26	TZD 7.4 7.5 7.6 7.8 7.9 7.10 (but see my notes for the Simple Harmonic Oscillator) 8.2 8.3 8.4 started on 8.5
Week of Jun 2	TZD Finished 8.5 8.6 8.7 8.8 9.2 9.3 9.5