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Question:

Use Einstein's photoelectric equation to show how from this graph, (i) Threshold frequency, and (ii) Planck's constant can be determined.

Solution:

y = φe
φ = hf₀, f₀ = threshold frequency
f₀ = φ/h
f₀ = y/e
y = ordinate of straight line
tan θ = m = slope = h/e
h = e × slope = e tan θ