Ray diagrams for lenses

This video shows the method of constructing ray diagrams for lenses

Physics for future presidents

Today in class we watched this you tube video lecture from UCLA Berkley.

Waves waves waves

Dear Students our last topic for 2009 is waves.

This is one of those topics where understanding the jargon is a key to success.

Some of the jargon (I mean key words and terms) you need to have some comprehension of include:

• light
• sound
• electromagnetic
• spectrum
• reflection
• refraction
• diffraction
• interference
• resonance
• constructive
• destructive
• curved
• mirrors
• lenses
• critical angle
• boundary
• frequency
• amplitude
• velocity
• wavelength
• pulse
• superposition

One of the most famous incidents involving resonance is featured in the clip below showing the collapse and ultimate destruction of the Tacoma Narrows Bridge.

The millennium Bridge another classic of engineering skill.

Getting towards the sharp end

The year has passed in a flash and the practice exams will be upon us from 10 September. The topics covered for us include Mechanics, Electricity and Nuclear physics. Along with the practice exam we also have two internal assessments these are the practical test and the Physics in an integrated context. On the basis that there is no point reinventing the wheel I have done a quick snoop on resources made available by other school's web sites. One of the best is from Wanganui high school:
Yr 12 Physics

Why is AC used rather than DC to supply electricity

Attention Mr G.

I hope you are regularly visiting the Physics blog. Here is some stuff that may help you answer your BIG question.

Stolen for Wikipedia

"Centralized power generation became possible when it was recognized that alternating current electric power lines can transport electricity at low costs across great distances by taking advantage of the ability to change voltage across the distribution path using power transformers. The voltage is raised at the point of generation (a representative number is a generator voltage in the low kilovolt range) to a much higher voltage (tens of thousands to several hundred thousand volts) for primary transmission, followed by several downward transformations, to as low as that used in residential domestic use, such as, e.g., 120 / 240 VAC at 60 Hertz in North America and 230 / 400 VAC at 50 Hertz in Europe."

Transmission loss

The advantage of AC for distributing power over a distance is due to the ease of changing voltages with a transformer. Power is the product current × voltage (P = IV). For a given amount of power, a low voltage requires a higher current and a higher voltage requires a lower current. Since metal conducting wires have a certain resistance, some power will be wasted as heat in the wires. This power loss is given by P = I²R. Thus, if the overall transmitted power is the same, and given the constraints of practical conductor sizes, low-voltage, high-current transmissions will suffer a much greater power loss than high-voltage, low-current ones. This holds whether DC or AC is used.

Transforming DC power from one voltage to another was difficult and expensive due to the need for a large spinning rotary converter or motor-generator set, whereas with AC the voltage changes can be done with simple and efficient transformer coils that have no moving parts and require no maintenance. This was the key to the success of the AC system. Modern transmission grids regularly use AC voltages up to 765,000 volts. ^[10]

Alternating current transmission lines do have other losses not observed with direct current. Due to the skin effect, a conductor will have a higher resistance to alternating current than to direct current; the effect is measurable and of practical significance for large conductors carrying on the order of thousands of amperes. The increased resistance due to the skin effect can be offset by changing the shape of conductors from a solid core to a braid of many small wires.

Links:

War_of_Currents

Alternating_current

Electric_power_transmission

New Link

Check out the Physics podcasts site I have added to the "other sites" list. Imagine you could download a podcast onto your Ipod and secretly listen to Oldish American Men lecturing about Physics. If you tap your fingers a little your friends will probably think you are listening to some of that wild hippidy hop young peoples music.

MIT Physics

One of the major Universities in the states has put all it's course online. Here is a lecture on electricity and magnetism.
Ideal to use up any spare band width you have on your broadband plan. Not bad for learning about Physics either.

Voltage Divider

voltage divider

Equivalent Resistance

One important and very achievable skill you will all need to pick this year is how to calculate resistance in circuits. The clips that follow are clear explainations for solving the type of resistance problems you will face in Yr 12 Physics assessments.

Homework due Monday 8 June

Please complete activity 15A on electric feilds, from our Physics textbook. Don't forget senior subject reports will be written over the next weeks or so.

New Topic Electricity

Finally we have finished our Mechanics Marathon. Our new topic is electricity and we have started with the concept of electric field and its effect on charges. Here is what Wikipedia has to say about electric fields

Competition

Year twelve physics students your challenge is to produce the best flash cards from the handouts I gave you this morning. A prize will be awarded to the person who produces the best set at Tuesday's lesson. Go get creating!

Mechanics topic finished

We have come to the end of the Mechanics section of the course. Week four we will sit the common test. Now is the time to review all of the work we have done so far this year.

A good first step is check back through your text books and make sure you have attempted all the activities. Please let me know about any areas that you need help with and areas you like to have more explaination and examples of.

Central force experiment

Last day of term, last spell of the day no rest for year twelve physics.

Projectile motion

Projectile motion demonstration  here is a simple applet that captures some of the important features of P.M.


Solving projectile motion problems This link has some worked examples for solving P.M.problems.

Vectors and momentum

in depth vector concepts.

Momentum and Collisions

Physics Classroom Tutorial

Hi Physics Students

I have just added another site to the list of sites on the right hand side of the blog.

The Physics Classroom Tutorial is an online physics tutorial written for high school physics students. The tutorial was originally developed for physics students at Glenbrook South High School in Glenview, Illinois.

I think you will find the tutorial very useful if you are having difficulty with the Kinematic equations it also covers a number of other mechanics topics.

Relative Motion and Vector Addition

It is difficult to think of a more reliable source of scientific knowledge than a Japanese Game Show here is a short clip showing a relative motion demonstration.



Simple demonstration of vector addition.

Homework

Working on activities 7b and c of our physics text book

Homework

Due on Monday 16 February. 

Activity 7a questions 1 to 8

Vectors

Please make an effort to grasp the concept of vectors. There are a couple of links in the right sidebar that should help if you need to have further explaination.

Practical

Our first practical.

How can such a simple thing as a model car traveling down an inclined slope become such a mission of data collection, repeats and graphical analysis.

  Such are the joys of year 12 Physics.

Homework

Activity 7a question numbers 1 to 4.

Welcome to Yr 12 Physics 2009

Welcome to another year of Physics. I always find it an exciting time meeting my new students and trying to figure out what things are going to be like in the coming year. So far I like what I see. It was good to hear the range of reasons students had for choosing to study physics and having clear goals is sure to help motivate you to succeed well in this course.

The intentions of this blog include:

• To encourage students to use the resources available on the Internet to help in learning new skills and gaining knowledge about physics.
  
• To provide a mechanism to express dissatisfaction about any aspects of what is happening during the year in physics. (positive feedback is also welcome).
• To discuss or ask questions about any aspect of the course.
• To help you do as well as you possibly can in this subject.

One of my favourite physics web resources are YouTube videos. It would be great if our class can contribute our own small contribution to this ever increasing collection this year. 

One of the first things we will have to get our heads around this year is the concept of vector quantities and one of the simplest is the distinction between distance and displacement. Here is one persons explanation: 

Time to think about refreshing your memory about trigonometry?