Saturday, April 21, 2012

Investigating Momentum

·         You know that these situations are wrong, but why are they wrong?!

Guided discovery - Investigating Momentum
14 March 2012
07:20

When we collide two gliders on the

air track, what happens?

 

Situation 1: Elastic collision with a stationary glider

Initial

Initial speed of LH glider = ul = 1m/s

Initial speed of RH glider = ur = 0m/s

Image001

 

Final

Final speed of LH glider = vl = 0m/s

Final speed of RH glider = vr = 1m/s

Image002

 

We can represent this graphically as

 

Initial

Image003

Final

Image004

 

Conclusion

·         It appears that the speed is "transferred" to the RH glider

 

 

Situation 2: Inelastic collision with a stationary glider

Initial

Initial speed of LH glider = ul = 1m/s

Initial speed of RH glider = ur = 0m/s

Image005

 

Final

Final speed of LH glider = vl = 0.5m/s

Final speed of RH glider = vr = 0.5m/s

Image006

 

We can represent this graphically as

 

Initial

Image003

Final

Image007

 

Conclusion

·         Speed is conserved in the collision
·         Total Initial speed = Total Final speed

 

 

Situation 3: Head on collision

Initial

Initial speed of LH glider = ul = 1m/s

Initial speed of RH glider = ur = -1m/s

Image008

 

Final

Final speed of LH glider = vl = 0m/s

Final speed of RH glider = vr = 0m/s

Image009

 

We can represent this graphically as

 

Initial

Image010

Final

Image011

 

Conclusion

·         Velocity is conserved in the collision
·         Total Initial velocity = Total Final velocity

 

 

Situation 4: Head on collision with different masses

Initial

Initial speed of LH glider = ul = 1m/s

Initial speed of RH glider = ur = -1m/s

Image012

 

Final

Final speed of LH glider = vl = 0m/s

Final speed of RH glider = vr = 0m/s

Image013

 

Problem!

Our previous conclusion that

o    Velocity is conserved in the collision

doesn't hold for this situation!

 

Why do they move off to the left?

Because the RH glider has twice the mass

 

What could I change about the LH glider to make both gliders stop after the collision?

o    Double the mass (obvious)
o    Double the initial velocity

 

We can represent this graphically as

 

Initial

Image014

Final

Image015

 

So something is conserved in the collision, but what is it?

 

What does the area of the rectangles represent?!

 

Time to label our axes!

Image016

Final Conclusion

·         The area of the rectangles are mass x velocity
·         Momentum = mass x velocity
·         So momentum is conserved in collisions

Thursday, March 29, 2012

7.19 and 7.20

·         
7.19 understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei
·         7.20 understand the role played by the control rods and moderator when the fission process is used as an energy source to generate electricity
<<Fission for energy.pptm>>
<<DJFPh110chain2.swf>>
<<chain reaction animation.swf>>
<<reaction with control rods animation.swf>>

7.17 to 7.20 Plenary Answers
13 January 2012
14:17
1.  What is the process of splitting large nuclei called?

Fission

2.  How is 235U made to decay inside a nuclear reactor?

It is bombarded by a neutron to turn it into 236U which is unstable and rapidly decays

Image001

3.  
What are the generic names for the products of a fission reaction?

Two daughter nuclei and either two or three neutrons are produced

Image002

4.  
In what form is energy produced during a fission reaction?

Energy is released in the form of Kinetic Energy of the products of the reaction - the two daughter nuclei and the neutrons

5.  For a stable chain reaction to occur how many neutrons must, on average, collide with another nucleus of 235U?

Exactly one.  If the value is less than this the reaction will eventually finish.  If the value is more than this the reaction will very rapidly accelerate to explosive rates - utilised in nuclear weapons

Image003

6.  
What is the purpose of the moderator?

The moderator slows down the neutrons produced by fission so that they can be captured by other 235U nuclei and thus sustain the chain reaction

7.  What do the control rods do?

Control rods absorb excess neutrons in the reactor and thereby provide a method for controlling the chain reaction

Image004

reaction with control rods animation.swf Download this file

Fission for energy.pptm Download this file

DJFPh110chain2.swf Download this file

chain reaction animation.swf Download this file

7.17 and 7.18


A fuel that doesn’t burn.  What is it?

Answers

·         Uranium.  When Uranium atoms split into two (fission) they release energy which can be captured in a nuclear power station.  This is a nuclear reaction and is fundamentally different to burning (combustion is a chemical reaction)

7.17 and 7.18 starter 2
13 January 2012
14:02

How many protons and neutrons are there in

·         23592U?
·         23692U?

Answers

·         23592U = 92 protons; 143 neutrons.

This radioisotope of Uranium is commonly used as a fuel for nuclear power stations

·         23692U = 92 protons; 144 neutrons

This radioisotope of Uranium is highly unstable and is artificially created in nuclear power stations where it undergoes fission

7.17 and 7.18
12 January 2012
10:32
·         7.17 understand that a nucleus of U-235 can be split (the process of fission) by collision with a neutron, and that this process releases energy in the form of kinetic energy of the fission products
·         7.18 recall that the fission of U-235 produces two daughter nuclei and a small number of neutrons
<<Nuclear Fission.pptm>>
<<U235 fission animation.swf>>

PhET animation - nuclear fission
31 January 2012
13:34
<<nuclear-fission_en.jar>>
Website

Embed code for your blog
<div style="position: relative; width: 300px; height: 225px;"><a href="http://phet.colorado.edu/sims/nuclear-physics/nuclear-fission_en.jnlp" style="text-decoration: none;"><img src="
Media_httpphetcolorad_hbfjz
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U235 fission animation.swf Download this file

Nuclear Fission.pptm Download this file

Saturday, March 3, 2012

7.10 to 7.12 questions

1.              
What happens to the amount of ‘mother’ nuclei as time passes? - They will decay, possibly into another element
2.              What sort of radioisotope will decay the fastest - one with a long half life or one with a short half life? - One with short half life
3.              Does half life tell us exactly when a particular nucleus in a radioisotope will decay? - No, it is a random process. 
4.              What are the two definitions of half life? 1) Time taken for the activity of a sample to halve; 2) The time taken for the number of radioactive atoms in a sample to halve
5.              What does the activity of a source mean? - The amount of atoms in a sample that decays per second
6.              What is the unit of activity? - Becquerel (Bq)
7.              What will happen to the number of ‘mother’ nuclei after two half lives? - It will decreased to 1/4 of the original number
8.              What will happen to the activity of a source after two half lives? - It decreases to 1/4 of the original count

7.10 to 7.12 calculation questions (working in notebook)
1.  A radioisotope has a half life of 12 years. What fraction of the radioisotope will be left after 60 years? - 1/32
2.  If the activity of a sample falls to 1/64th of its original level after 2 hours, what is the half life of the sample? - 20 minutes
3.  The background radiation in a laboratory is 7 Bq. The count rate from a radioisotope is measured and it has a reading of 119 Bq. If the half life of the radioisotope is 10 minutes, what will be the reading 20 minutes later? - 28 Bq
4.  Potassium decays into argon.  The half life of potassium is 1.3 billion years.  A sample of rock from Mars is found to contain three argon atoms for every atom of potassium.  How old is the rock? 2.6 Billion Years                                     

7.10 to 7.12

·         
Smoke detectors use 241Am to emit alpha particles which pass through a small air gap before being detected.  If smoke particles are present they interrupt the beam of alpha particles and this triggers the alarm to go off
·         Tomorrow, will the 241Am still be as radioactive?
·         Next year, will the 241Am still be as radioactive?
·         In a thousand years, will the 241Am still be as radioactive?

Answers

·         To answer the questions, we need to know the half life of Americium-241which is 432 years
·         Tomorrow and even next year its activity will hardly have changed at all (sensible for a smoke detector - you don't want it to suddenly stop working!)
·         In a thousand years its activity will have dropped to about a quarter

·         
7.10 understand that the activity of a radioactive source decreases over a period of time and is measured in becquerels
·         7.11 recall the term ‘half-life’ and understand that it is different for different radioactive isotopes
·         7.12 use the concept of half-life to carry out simple calculations on activity

Half-life of Different Isotopes

·         

Half life.pptx Download this file

interactive simple half life calculations.swf Download this file

Decay of Balonium - exponential graph.swf Download this file

PhET animation - alpha decay
31 January 2012

13:34

<<alpha-decay_en.jar>>

PhET animation - beta decay
31 January 2012
13:34
<<beta-decay_en.jar>>

7.6 and 7.7

·         
7.6 describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the three main types of radiation

·         
7.7 understa
nd how to complete balanced nuclear equations

Balanced nuclear equations.pptx Download this file

alpha decay of Am241 animation.swf Download this file


Did you spot the deliberate mistake on this animation?

 

beta decay of C14 animation.swf Download this file

Answer
The symbol for Neptunium is Np not NP!

Image001

interactive alpha and beta decay eqns.swf Download this file

Balanced nuclear equations plenary mulichoice question.pptx Download this file

7.4 to 7.9 plenaries

alpha, beta, gamma summary table.pptx Download this file

a,b,g and ionisation plenary questions.pptx Download this file

7.9

7.9 recall the sources of background radiation

Whys Guy

background radiation.pptx Download this file

7.8

7.8 understand that ionising radiations can be detected using a photographic film or a Geiger-Muller detector

detection of radiation.pptx Download this file

7.3

7.3 understand the terms atomic (proton) number, mass (nucleon) number and isotope
Website

Embed code for your blog
<div style="position: relative; width: 300px; height: 226px;"><a href="http://phet.colorado.edu/sims/build-an-atom/build-an-atom_en.jnlp" style="text-decoration: none;"><img src="
Media_httpphetcolorad_bxjbg
" alt="Build an Atom" style="border: none;" width="300" height="226"/><div style="position: absolute; width: 200px; height: 80px; left: 50px; top: 73px; background-color: #FFF; opacity: 0.6; filter: alpha(opacity = 60);"></div><table style="position: absolute; width: 200px; height: 80px; left: 50px; top: 73px;"><tr><td style="text-align: center; color: #000; font-size: 24px; font-family: Arial,sans-serif;">Click to Run</td></tr></table></a></div>

Website

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<div style="position: relative; width: 300px; height: 226px;"><a href="http://phet.colorado.edu/sims/build-an-atom/isotopes-and-atomic-mass_en.jnlp" style="text-decoration: none;"><img src="
Media_httpphetcolorad_fagrc
" alt="Isotopes and Atomic Mass" style="border: none;" width="300" height="226"/><div style="position: absolute; width: 200px; height: 80px; left: 50px; top: 73px; background-color: #FFF; opacity: 0.6; filter: alpha(opacity = 60);"></div><table style="position: absolute; width: 200px; height: 80px; left: 50px; top: 73px;"><tr><td style="text-align: center; color: #000; font-size: 24px; font-family: Arial,sans-serif;">Click to Run</td></tr></table></a></div>

Isotopes.ppt Download this file

Monday, February 27, 2012

7.2

Tell the person next to you…

·         The names of 3 subatomic particles
·         What properties do they have?

atomic structure - electrons orbiting the nucleus.swf Download this file

sub-atomic particles - drag and drop.swf Download this file

·         7.2 describe the structure of an atom in terms of protons, neutrons and electrons and use symbols such as 146C to describe particular nuclei

Proton number and mass number.ppt Download this file

atomic structure of Li - mass and proton numbers.swf Download this file

P7 student objectives sheet

P7 IGCSE Physics Student Objectives.doc Download this file

P7 student objectives sheet

P7 IGCSE Physics Student Objectives.doc Download this file