# GRE Physics GR 1777 Problem Solution

## 014. Quantum Mechanics (Planck length), Dimensional Analysis

### Solution

If you don’t know the Planck length, that’s fine. This question asks that you know about the dimensional analysis.

The unit of the length should be . To find the proper expression for length, we construct the equation like this:

The dimensions of this equation gives

We can easily calculate their orders.

Therefore, the Planck length is

### Alternative Solution

If you already know about the Planck length, then you have nothing to worry about.

The Planck length is

### Answer

(A)