As a student is performing a double slit experiment to determine the wavelength of a light source, she realizes that the nodal lines are too close together to be accurately measured. To increase the distance between the nodal lines, she could:

To increase the distance between the nodal lines as it may be difficult to determine the wavelength of the light source because the nodal lines are too close, the student should spread the fringe pattern by having to be able to decrease the separation of the slit.