# GRE Physics GR 1777 Problem Solution

## 023. Quantum Mechanics (Positronium)

• Rydberg constant for positronium may be calculated from the reduced mass

$R_M = R_\infty \Big( \frac{M}{m_e + M} \Big) = R_\infty \Big( 1 + \frac{m_e}{M} \Big)^{-1}$

### Solution

(B) 0.5 $R_\infty$