Gently tap the back of one mirror until the interference pattern shifts by exactly one fringe. Notice how such a small push corresponds to one fringe shift. The distance that you push the mirror is too small to measure directly with a ruler at your lab table.Using the quantitative relationship between the fringe pattern and path difference, calculate the distance that you moved the mirror for one fringe shif. Briefy compare this calculated distance to the size of a bacterium, which is about 106meters long