Experimental negative work function?

[teroenza]

Homework Statement

I have experimentally determined the work function from the intercepts of a fit line in graph of stopping potential (J) versus frequency (Hz). This is from a photoelectric effect lab. The value of the intercept, which I believe is that of the work function, is returned as negative. (the "a" value in the boxes). I know I am getting hung up mentally on a simple sign issue, but why is this value negative? Is this a sign convention indicating energy must enter the material to knock particles (electrons in my case) off?

Homework Equations

y= bx +a

Stopping Potential = h*frequency - work function

The Attempt at a Solution

My graph is attached.

 

[member 553083]

The negative "a" value of the fit line is -1.85 V. The negative sign in this equation indicates that energy must enter the material to knock electrons off, as you suggested. This is because the equation for stopping potential is Stopping Potential = h*frequency - work function. Since the work function is a negative value, energy must be added to the system in order for electrons to be released.