Edexcel A-Level Physics 9PH0
Working as a Physicist
Mechanics
Electric Circuits
Materials
Waves and Particle Nature of Light
Further Mechanics
Electric and Magnetic Fields
Nuclear and Particle Physics
Thermodynamics
Space
Nuclear Radiation
Gravitational Fields
Oscillations
Nuclear and Particle Physics
Particle tracks, conservation laws and why high energies are needed
- 3 things to know
- Papers 1 and 3
Overview
Recall questions on reading momentum and charge from a track, why an uncharged particle leaves none, applying conservation at a vertex, and why high energies are required.
What you need to know
Answer each one before you reveal it.
How is conservation of energy applied to an interaction between particles?
Why does a head-on collision between two beams make more energy available than firing a beam at a stationary target?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How is a particle's momentum determined from its track in a detector?
Model answer
The radius of curvature of the track is measured and used in p = BQr with the known magnetic flux density and the particle's charge.
- 2
How can the sign of a particle's charge be identified from its track?
Model answer
Particles of opposite charge experience magnetic forces in opposite directions in the same field, so their tracks curve in opposite senses.
- 3
Why does a track in a detector often spiral inwards rather than staying a circle?
Model answer
The particle loses energy and momentum by ionising the material it passes through, so the radius r = p/(BQ) shrinks steadily along the track.
- 4
On what general principle does a detector register the passage of a charged particle?
Model answer
The particle ionises atoms of the detecting material along its path, and the ions and electrons released produce a visible trail, a pulse of current or a flash of light.
- 5
Why does an uncharged particle leave no track in a detector?
Model answer
It does not ionise the material it passes through, so its presence must be deduced from the tracks of charged particles produced when it decays or interacts.
- 6
What does a short, thick track tell you about the particle that made it?
Model answer
It was strongly ionising, producing many ion pairs per unit length, so it lost energy quickly and came to rest after a short distance.
Other ways to work this
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