Electron momentum
About points...
We associate a certain number of points with each exercise.
When you click an exercise into a collection, this number will be taken as points for the exercise, kind of "by default".
But once the exercise is on the collection, you can edit the number of points for the exercise in the collection independently, without any effect on "points by default" as represented by the number here.
That being said... How many "default points" should you associate with an exercise upon creation?
As with difficulty, there is no straight forward and generally accepted way.
But as a guideline, we tend to give as many points by default as there are mathematical steps to do in the exercise.
Again, very vague... But the number should kind of represent the "work" required.
When you click an exercise into a collection, this number will be taken as points for the exercise, kind of "by default".
But once the exercise is on the collection, you can edit the number of points for the exercise in the collection independently, without any effect on "points by default" as represented by the number here.
That being said... How many "default points" should you associate with an exercise upon creation?
As with difficulty, there is no straight forward and generally accepted way.
But as a guideline, we tend to give as many points by default as there are mathematical steps to do in the exercise.
Again, very vague... But the number should kind of represent the "work" required.
About difficulty...
We associate a certain difficulty with each exercise.
When you click an exercise into a collection, this number will be taken as difficulty for the exercise, kind of "by default".
But once the exercise is on the collection, you can edit its difficulty in the collection independently, without any effect on the "difficulty by default" here.
Why we use chess pieces? Well... we like chess, we like playing around with \(\LaTeX\)-fonts, we wanted symbols that need less space than six stars in a table-column... But in your layouts, you are of course free to indicate the difficulty of the exercise the way you want.
That being said... How "difficult" is an exercise? It depends on many factors, like what was being taught etc.
In physics exercises, we try to follow this pattern:
Level 1 - One formula (one you would find in a reference book) is enough to solve the exercise. Example exercise
Level 2 - Two formulas are needed, it's possible to compute an "in-between" solution, i.e. no algebraic equation needed. Example exercise
Level 3 - "Chain-computations" like on level 2, but 3+ calculations. Still, no equations, i.e. you are not forced to solve it in an algebraic manner. Example exercise
Level 4 - Exercise needs to be solved by algebraic equations, not possible to calculate numerical "in-between" results. Example exercise
Level 5 -
Level 6 -
When you click an exercise into a collection, this number will be taken as difficulty for the exercise, kind of "by default".
But once the exercise is on the collection, you can edit its difficulty in the collection independently, without any effect on the "difficulty by default" here.
Why we use chess pieces? Well... we like chess, we like playing around with \(\LaTeX\)-fonts, we wanted symbols that need less space than six stars in a table-column... But in your layouts, you are of course free to indicate the difficulty of the exercise the way you want.
That being said... How "difficult" is an exercise? It depends on many factors, like what was being taught etc.
In physics exercises, we try to follow this pattern:
Level 1 - One formula (one you would find in a reference book) is enough to solve the exercise. Example exercise
Level 2 - Two formulas are needed, it's possible to compute an "in-between" solution, i.e. no algebraic equation needed. Example exercise
Level 3 - "Chain-computations" like on level 2, but 3+ calculations. Still, no equations, i.e. you are not forced to solve it in an algebraic manner. Example exercise
Level 4 - Exercise needs to be solved by algebraic equations, not possible to calculate numerical "in-between" results. Example exercise
Level 5 -
Level 6 -
Question
Solution
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Exercise:
Calculate the momentum of an electron with EkO kinetic energy.
Solution:
The kinetic energy is comparable to the rest energy of the electron E_ ErO therefore the problem has to be treated relativistically. The total energy of the electron is the of its rest energy and its kinetic energy: E EtF Ek + Er Et approx EtP The "relativistic pythagoras" relates the total energy to the momentum: E^ leftp cright^ + E_^ Solving for the product p c yields the momentum in the practical unit sielectronvoltper c: p c pevF sqrtleftEtright^-leftErright^ pev approx pevP i.e. p &approx resultkiloelectronvoltper c To convert to the unit the energy in electronvolt is converted to joule factor e and divided by the speed of light: p fracpevncc pe approx resultpeS medskip A classical calculation would give p_mathrmcl pnrF pnr approx pnrS i.e. a value that is about percent too small. At a kinetic energy of about a quarter of the rest energy the relativistic treatment is clearly necessary.
Calculate the momentum of an electron with EkO kinetic energy.
Solution:
The kinetic energy is comparable to the rest energy of the electron E_ ErO therefore the problem has to be treated relativistically. The total energy of the electron is the of its rest energy and its kinetic energy: E EtF Ek + Er Et approx EtP The "relativistic pythagoras" relates the total energy to the momentum: E^ leftp cright^ + E_^ Solving for the product p c yields the momentum in the practical unit sielectronvoltper c: p c pevF sqrtleftEtright^-leftErright^ pev approx pevP i.e. p &approx resultkiloelectronvoltper c To convert to the unit the energy in electronvolt is converted to joule factor e and divided by the speed of light: p fracpevncc pe approx resultpeS medskip A classical calculation would give p_mathrmcl pnrF pnr approx pnrS i.e. a value that is about percent too small. At a kinetic energy of about a quarter of the rest energy the relativistic treatment is clearly necessary.
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Exercise:
Calculate the momentum of an electron with EkO kinetic energy.
Solution:
The kinetic energy is comparable to the rest energy of the electron E_ ErO therefore the problem has to be treated relativistically. The total energy of the electron is the of its rest energy and its kinetic energy: E EtF Ek + Er Et approx EtP The "relativistic pythagoras" relates the total energy to the momentum: E^ leftp cright^ + E_^ Solving for the product p c yields the momentum in the practical unit sielectronvoltper c: p c pevF sqrtleftEtright^-leftErright^ pev approx pevP i.e. p &approx resultkiloelectronvoltper c To convert to the unit the energy in electronvolt is converted to joule factor e and divided by the speed of light: p fracpevncc pe approx resultpeS medskip A classical calculation would give p_mathrmcl pnrF pnr approx pnrS i.e. a value that is about percent too small. At a kinetic energy of about a quarter of the rest energy the relativistic treatment is clearly necessary.
Calculate the momentum of an electron with EkO kinetic energy.
Solution:
The kinetic energy is comparable to the rest energy of the electron E_ ErO therefore the problem has to be treated relativistically. The total energy of the electron is the of its rest energy and its kinetic energy: E EtF Ek + Er Et approx EtP The "relativistic pythagoras" relates the total energy to the momentum: E^ leftp cright^ + E_^ Solving for the product p c yields the momentum in the practical unit sielectronvoltper c: p c pevF sqrtleftEtright^-leftErright^ pev approx pevP i.e. p &approx resultkiloelectronvoltper c To convert to the unit the energy in electronvolt is converted to joule factor e and divided by the speed of light: p fracpevncc pe approx resultpeS medskip A classical calculation would give p_mathrmcl pnrF pnr approx pnrS i.e. a value that is about percent too small. At a kinetic energy of about a quarter of the rest energy the relativistic treatment is clearly necessary.
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