Mass & Energy
Physics: AQA A Level, topic 12.3.5
Mass and Energy Equivalence
Mass and energy can be shown to be equivalent.
Mass varies with speed
- As an object gains velocity, it also gains mass.
- This is given by the formula:
- m is the moving mass.
- is the mass at rest.
- v is the moving velocity.
- c is the speed of light.
Einstein's relativity
- Einstein extended relativistic mass to produce:
- .
- This shows that mass and energy are equivalent.
Bertozzi's Experiment
Bertozzi’s experiment sought to provide experimental proof that mass increases with velocity.
Method
- Bertozzi used linear particle accelerators to accelerate electrons into an aluminium disc.
- He recorded the time taken for the electrons to reach the disc, along with the energy provided to the electron.
- He used the heat generated on the aluminium disc to calculate the final velocity of the electrons.
- He did this by equating heat and kinetic energy.
Results
- He found that the velocities of the electrons did not continue to increase as he supplied more energy to the electrons.
- Instead, they approached a maximum value of c - the speed of light.
- This is the first evidence of special relativity.
Test yourself on Mass & Energy
What is the correct formula to link mass with velocity?
How did Bertozzi calculate the kinetic energy before impact with the aluminium disc?
Bertozzi's Experiment
Bertozzi found that particles approaches what speed?