Summary of Nuclear Physics

Nuclear Physics Summary

Quantum Physics Summary

Quantum Physics Summary

Do you know the answer to this question?

This is a billion dollar question. Do you have the answer?

This question is extracted from Department of Louisiana 2013-2014 practice test for Grade 8 Maths and I was aware of this question through Rhett Allain's blog.

The Universe in a Nutshell - Michio Kaku

This is probably one of the most concise, most interesting, most informative and most layman introduction to the four fundamental forces that I have watched. It kept me riveted to the screen for 42 mins even though I knew every facts explained in the video.

This video is a must for upper secondary and junior college students to watch as an introduction to the four fundamental forces and a brief glimpse of the wonder and beauty of Physics. It should replace the boring five minutes we accord to the fundamental forces when we lecture.

Finding analogies to abstract Physics concepts

This is a hilarious method to introduce the atom to a gangster. However it works! In learning we need to find our personal analogies to have enduring understanding.

How is energy being transferred in a conventional circuit? A new but coherent perspective.

I saw this videos some years ago and shared with my graduating class students even though it is not the usual way energy transferred in circuits is being taught and assessed.



Two days ago, I watched this video again while searching for videos for Quantum Physics. I was determined to find out how energy can be transferred outside the wire!

Few interesting concepts from my internet research, some was new to me before my research:

• The battery (source) causes a different distribution of surface charges along the circuit, this indicate a slightly non-neutrally along short sections in the circuit. This is possible as there is dynamic equilibrium (analogous to a pressure gradient in fluid flow in pipes) in the circuit. Conventional teaching claims that the entire circuit is neutral because the net charge is zero, which is correct, but we incorrectly extend it to mean that every section of the wire must be neutral.
• The distribution of surface charges result in (a) an electric field along the wire and (b) electrostatic field that extend radially from the wire.
• The electric field along the wire is what we normally associate as the potential difference between two points in a circuit (remember that E = -dV/dr). 
• The magnetic field associated with the movement charges in the wire is perpendicular (tangential to "circles" around the wire) to the radial electric field due to the surface charges. 
• The cross product E x B gives the Poynting vector that gives the direction of energy flow/transfer. This is how energy is transferred through space outside the wire!

The following are some of the articles I have gathered the past two days:

• Surface Charges and Poynting Vector - Relatively easy to understand the surface charge distribution.
• HyperPhysics Poynting Vector - Introduction to Poynting Vector.
• Energy transfer in electrical circuits: A qualitative account, Igal Galili and Elisabetta Goihbarg - Article from Americal Journal of Physics which is very reputable and I would consider it to be a trustworthy source.
• A unified treatment of electrostatics and circuits, B. A. Sherwood and R. W. Chabay - a more detail development of the concepts compared to the previous Am. J. Phys. article. Possibly a guide for teachers who want to challenge their students' understanding of circuits.

Pre-lecture activity on Quantum Physics

Current Balance Demonstration/Experiment

Photo above showing the wire frame where current will pass through. The frame is completely between the poles of the u-shaped magnet (North is red) during experiment.

Photo above shows that the wire frame is not in contact with the magnet. 

The video of the experiment is embedded below or http://youtu.be/nkS7wCCzGiY. You may pause the video at each current reading to obtain the following data. The balance is zeroed to measure ony the gain/loss in mass of magnet.

Questions: What is the direction of the force on the wire frame and the magnet? Why is the magnet getting "heavier"? When the current is reversed (http://youtu.be/hnU4g4NBXXo), why is the magnet getting "lighter"?

The electronic balance gives reading in grammes. The magnetic force is obtained by multiplying the balance reading by 10 N/kg (or 9.8 N/kg if you want to be accurate). Since

F = BIL

Plot a graph of magnetic force F against current I in the wire frame. If a linear trend is obtained, the gradient will be BL where L is measured to be 4.0 cm. 

Gradient = 4.466 mN/A = 0.004466 N/A

Therefore B = 0.004466/0.040 = 0.11 T

This value is reasonable because the magnetic flux density of the magnet should be much greater than Earth's intrinsic magnetic field (~10 nT) and flux density of more than 1 T is hard to obtain in common school lab.

Demonstrations and questions on electrons in electric or magnetic field

Demo 1 - Increasing deflection plates potential difference

Questions:

• What do you notice about the electron beam when the deflection plates p.d. is increased?
• Explain your answer to the previous question.

Demo 2 - Increasing accelerating potential  

Questions:

• What do you notice about the electron beam when the accelerating p.d. is increased?
• Explain your answer to the previous question.

Demo 3 - Electron beam in uniform magnetic field while accelerating potential is increased

Questions:

• What do you notice about the electron beam in uniform when the accelerating potential is increased?
• Explain your answer to the previous question.

Demo 4 - Electron in increasing magnetic field

Questions:

• What do you notice about the electron beam in uniform field when magnetic flux density is increased?
• Explain your answer to the previous question.

Demo 5 - Electrons enter the magnetic field not at right angle (Helical motion)

Questions:

• What do you notice about the electron enter the magnetic field not at right angle?
• Explain your answer to the previous question. The video below may help you.

How does a potentiometer work?