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Pair Annihilation
Pair annihilation is the process in which a particle and its antiparticle interact and convert their mass-energy into other particles, commonly photons.
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Pair Annihilation
What is it?
Pair annihilation is the process in which a particle and its antiparticle interact and convert their mass-energy into other particles, commonly photons.
In simple words
- Annihilation demonstrates conversion of rest mass into radiation.
Recommended for Class 12
Full school-level explanation
Pair annihilation is the process in which a particle and its antiparticle interact and convert their mass-energy into other particles, commonly photons.
Conservation
For an electron and positron at rest or nearly at rest: e⁻ + e⁺ → 2γ Two photons are produced in the simplest case. If the electron and positron annihilate approximately at rest: each photon has energy: Eγ≈mec²≈0.511MeV and the two photons travel in opposite directions to conserve momentum. Total photon energy: ≈1.022MeV ignoring initial kinetic energy. The process obeys: energy conservation; momentum conservation; * electric charge conservation. Pair annihilation is essentially the reverse idea of pair production.
Formula / Key Relation
**e⁻+e⁺→2γ** At rest: **Eγ≈0.511MeV each**
Remember
- e⁻+e⁺→2γ
- Eγ≈0.511MeV each
Deeper understanding
Go deeper on Pair Annihilation: connect the definition to reasons, relationships, exceptions, and exam wording.
Common mistakes
Exam focus
Annihilation
Exam focus
Quick revision
- e⁻+e⁺→2γ
- Eγ≈0.511MeV each
- Conservation: For an electron and positron at rest or nearly at rest: e⁻ + e⁺ → 2γ Two photons are produced
- Formula / Key Relation: e⁻+e⁺→2γ At rest: Eγ≈0.511MeV each
- Annihilation demonstrates conversion of rest mass into radiation.
For long answers on Pair Annihilation: define clearly → explain the main parts → give one example → state one exam caution.
Exam Focus
Exam Focus
Important points
- e⁻+e⁺→2γ
- Eγ≈0.511MeV each
- Conservation: For an electron and positron at rest or nearly at rest: e⁻ + e⁺ → 2γ Two photons are produced
- Formula / Key Relation: e⁻+e⁺→2γ At rest: Eγ≈0.511MeV each
Important formulas
- e⁻+e⁺→2γ
- Eγ≈0.511MeV each
Common exam traps
- Do not say energy disappears.
- Mass-energy is converted.
Long question structure
Definition → key parts → example → exam caution
Common Mistakes
Common Mistakes
- Mistake
Do not say energy disappears.
- Mistake
Mass-energy is converted.
- Mistake
Do not say energy disappears.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
e⁻+e⁺→2γ
Eγ≈0.511MeV each
Conservation: For an electron and positron at rest or nearly at rest: e⁻ + e⁺ → 2γ Two photons are produced
Formula / Key Relation: e⁻+e⁺→2γ At rest: Eγ≈0.511MeV each
Pair annihilation is the process in which a particle and its antiparticle interact and convert their mass-energy into other particles, commonly photons.
e⁻+e⁺→2γ
- Definition
- Pair annihilation is the process in which a particle and its antiparticle interact and convert their mass-energy into other particles, commonly photons.
- Formula
- e⁻+e⁺→2γ
- Critical warning
- Do not say energy disappears.
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Exam Practice
Define
Q1. Define Pair Annihilation.
Explain
Q2. Explain: Conservation.
Example
Q3. Give one clear example of Pair Annihilation and say why it fits.
Mistake
Q4. State one common mistake students make about Pair Annihilation.
Exam note
Q5. Write a short exam note on Pair Annihilation: definition, two points, one example.
Sources & References
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.