1. What about time ? What about their traces ?
How do particles move ???
What about time ?
What about their traces ?
5/6/2019
Dora Wagner HST 2001
Dora Wagner

2. What do we measure?
What do we know ?
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Dora Wagner HST 2001

3. What does velocity mean ?
“How quickly an object moves from one point to another !”
“The distance moved per unit of time.”
“The rate of change of displacement.”
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Dora Wagner HST 2001

4. Now the formula : V = Ds ------- Dt Dt : time interval
Ds : distance travelled
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Dora Wagner HST 2001

5. … the steeper, the faster !
How fast? How slow ?
distance
… the steeper, the faster !
time
5/6/2019
Dora Wagner HST 2001

6. But nothing can go faster than light !
The speed of light is
c = m/s,
and...
… all the particles inside
the bubble chamber were
travelling nearly as fast
as light !
5/6/2019
Dora Wagner HST 2001

7. Particles are interacting and decaying in a bubble chamber !
… are all particles recorded ?
… are there some, which don’t leave traces ?
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Dora Wagner HST 2001

8. … the particles… ? … where do they come from ?
… where are they going to ?
… how do they move ?
… what do their traces look like ?
… are they going straight or curved ?
… how long do they stay ?
5/6/2019
Dora Wagner HST 2001

9. What is the smallest interval of time you can imagine ?
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Dora Wagner HST 2001

10. Then it materialized into an electron…
LOOK !
A photon travelled between the two marked points. The distance was exactly
11.5 cm!
Then it materialized into an electron…
…and a positron.
5/6/2019
Dora Wagner HST 2001

11. Can you calculate the time taken by the photon?
Ds = cm
Dt = ?
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Dora Wagner HST 2001

12. REMEMBER ! Ds v = ------- Dt c = 300 000 000 m/s, 5/6/2019
Dora Wagner HST 2001

13. Unbelievable ?
Dt = Check your result
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Dora Wagner HST 2001

14. … less than a billionth of a second !
Dt = 383 ps (picoseconds)
… less than a billionth of a second !
5/6/2019
Dora Wagner HST 2001