Massless particles
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:
Show that for a massless particle e.g. a photon the momentum is given by the expression p fracEc where E is the particles energy.
Solution:
The relation between energy momentum and mass of a particle is E^ leftp cright^ + leftm c^right^ For a massless particle m the second term on the right hand side vanishes: E^ leftp cright^ + left c^right^ leftp cright^ Since both the energy and the momentum are positive taking the square root yields E p c and therefore p fracEc quad square medskip Note that a massless particle can never be at rest: with betafracpcE it always moves at the speed of light. The result is also consistent with the quantum mechanical description of a photon where E h f and c lambda f lead to the well known expression p frach fc frachlambda In particle physics the momentum is often stated in the practical unit sielectronvoltper c in which case the conversion is not necessary at all and the momentum is simply p fracEc kiloelectronvoltper c.
Show that for a massless particle e.g. a photon the momentum is given by the expression p fracEc where E is the particles energy.
Solution:
The relation between energy momentum and mass of a particle is E^ leftp cright^ + leftm c^right^ For a massless particle m the second term on the right hand side vanishes: E^ leftp cright^ + left c^right^ leftp cright^ Since both the energy and the momentum are positive taking the square root yields E p c and therefore p fracEc quad square medskip Note that a massless particle can never be at rest: with betafracpcE it always moves at the speed of light. The result is also consistent with the quantum mechanical description of a photon where E h f and c lambda f lead to the well known expression p frach fc frachlambda In particle physics the momentum is often stated in the practical unit sielectronvoltper c in which case the conversion is not necessary at all and the momentum is simply p fracEc kiloelectronvoltper c.
Meta Information
Exercise:
Show that for a massless particle e.g. a photon the momentum is given by the expression p fracEc where E is the particles energy.
Solution:
The relation between energy momentum and mass of a particle is E^ leftp cright^ + leftm c^right^ For a massless particle m the second term on the right hand side vanishes: E^ leftp cright^ + left c^right^ leftp cright^ Since both the energy and the momentum are positive taking the square root yields E p c and therefore p fracEc quad square medskip Note that a massless particle can never be at rest: with betafracpcE it always moves at the speed of light. The result is also consistent with the quantum mechanical description of a photon where E h f and c lambda f lead to the well known expression p frach fc frachlambda In particle physics the momentum is often stated in the practical unit sielectronvoltper c in which case the conversion is not necessary at all and the momentum is simply p fracEc kiloelectronvoltper c.
Show that for a massless particle e.g. a photon the momentum is given by the expression p fracEc where E is the particles energy.
Solution:
The relation between energy momentum and mass of a particle is E^ leftp cright^ + leftm c^right^ For a massless particle m the second term on the right hand side vanishes: E^ leftp cright^ + left c^right^ leftp cright^ Since both the energy and the momentum are positive taking the square root yields E p c and therefore p fracEc quad square medskip Note that a massless particle can never be at rest: with betafracpcE it always moves at the speed of light. The result is also consistent with the quantum mechanical description of a photon where E h f and c lambda f lead to the well known expression p frach fc frachlambda In particle physics the momentum is often stated in the practical unit sielectronvoltper c in which case the conversion is not necessary at all and the momentum is simply p fracEc kiloelectronvoltper c.
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