OCR A-Level Physics B H557
Planning
Implementing
Analysis
Evaluation
Practical Skills
Use of Apparatus and Techniques
Fundamental Data Analysis
Imaging and Signalling
Sensing
Mechanical Properties of Materials
Waves and Quantum Behaviour
Space, Time and Motion
Creating Models
Out Into Space
Our Place in the Universe
Matter: Very Simple
Matter: Hot or Cold
Electromagnetism
Charge and Field
Probing Deep Into Matter
Ionising Radiation and Risk
Probing Deep Into Matter
Relativistic energy and the relativistic factor
- 3 things to know
- Components 01, 02 and 03
Overview
Recall questions on rest energy from rest mass, electron and proton values in MeV, evaluating the factor at high speeds, total and kinetic energy, and why no massive particle reaches light speed.
What you need to know
Answer each one before you reveal it.
Calculate the rest energy of an electron in joules.
Express the rest energy of an electron in MeV.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Write the relationship between the rest mass of a particle and its rest energy.
Model answer
The rest energy is Erest = mc², where m is the rest mass and c is the speed of light in a vacuum.
- 2
Calculate the rest energy of an electron in joules.
Model answer
Erest = mc² = 9.11 × 10⁻³¹ × (3.00 × 10⁸)² = 8.2 × 10⁻¹⁴ J.
- 3
Express the rest energy of an electron in MeV.
Model answer
Dividing 8.2 × 10⁻¹⁴ J by 1.60 × 10⁻¹⁹ gives about 5.1 × 10⁵ eV, which is 0.51 MeV.
- 4
Calculate the rest energy of a proton in MeV.
Model answer
Erest = 1.673 × 10⁻²⁷ × (3.00 × 10⁸)² = 1.5 × 10⁻¹⁰ J, which is about 940 MeV.
- 5
Write the expression for the relativistic factor of a particle moving at speed v.
Model answer
The relativistic factor is γ = 1/√(1 − v²/c²).
- 6
What is the value of the relativistic factor for a particle at rest?
Model answer
The relativistic factor is 1, because v is zero and the square root reduces to 1.
Other ways to work this
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