Light from a sodium lamp of wavelength = 698 nm illuminates two narrow slits. The fringe spacing on a screen 1.8 m behind the slits is 0.40 mm. What is the spacing between the two slits, in mm? Your answer needs to have 2 significant figures, including the negative sign in your answer if needed. Do not include the positive sign if the answer is positive. No unit is needed in your answer, it is already given in the question statement.

Light from a sodium lamp of wavelength = 698 nm illuminates two narrow slits. The fringe spacing on a screen 1.8 m behind the slits is 0.40 mm. What is the spacing between the two slits, in mm? Your answer needs to have 2 significant figures, including the negative sign in your answer if needed. Do not include the positive sign if the answer is positive. No unit is needed in your answer, it is already given in the question statement.