Question

Use the following photoelectric graph to answer the following question:

Answer 1

The photoelectric effect is obtained when you shine a light on a material, resulting in the emission of electrons.

The kinetic energy of the electrons depends on the frequency of the light:
K = h(f - f₀)

where:
K = kinetic energy 
h = Planck constant
f = light frequency
f₀ = threshold frequency

Rearranging the formula in the form y = m·x + b, we get:
K = hf - hf₀
where:
K = dependent variable
f = indipendent variable
h = slope
hf₀ = y-intercept

Every material has its own threshold frequency, therefore, what stays constant for all the materials is h = Planck constant (see picture attached).

Hence, the correct answer is C) the slope.