The relation between phase difference ($\mathrm{\Delta \phi }$) and path difference ($\mathrm{\Delta x}$) is 

• A

  $\mathrm{\Delta \phi }=\frac{2\mathrm{\pi }}{\mathrm{\lambda }}\mathrm{\Delta x}$

• B

  $\mathrm{\Delta \phi }=2\mathrm{\pi \lambda \Delta x}$

• C

  $\mathrm{\Delta \phi }=\frac{2\mathrm{\pi \lambda }}{\mathrm{\Delta x}}$

• D

  $\mathrm{\Delta \phi }=\frac{2\mathrm{\Delta x}}{\mathrm{\lambda }}$