Help Needed: Calculating Slit Distance Using Interfringe Value

[Cyannaca]

Hi, I would need help with this problem.

A beam of light (628 nm) passes through 2 parallel slits in a screen, forming a pattern in which the interfringe is equal to 0,5 cm. If the distance between the slit and the screen is equal to 2,4 m, what is the distance between the slits?

The answer is 0,3 mm but I always get 1,5 which is way too high
I don't really understand how to use the interfringe value...

 

[Astronuc]

Try this - http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/slits.html#c1

 

[Dr.Brain]

The dsitance between the slits will be same as one fringe width iin case of perfect interference but may deviate in case of enchanced diffraction effects in interference .

BJ

 

[lightgrav]

The difference in path length between the two contributions
occurs right at the slits ... d sin (theta) , where theta is the deflection angle.
for the "most constructive" interference, the path length difference is an integer wavelength.