Key relationship
Kmax=hν−φ when hν>φ; eVs=Kmax; ν₀=φ/h.
Physics · Class 12
Photoelectric threshold
Dual Nature of Radiation & Matter
A photon must supply the work function before an electron can escape. Its remaining energy is the maximum kinetic energy. Greater intensity increases emission rate above threshold, while greater frequency raises maximum electron energy.
Open the interactive experiment →Photoelectric threshold
ஃபோட்டான் ஆற்றல் வேலைச் செயல்பாட்டை விட அதிகமாக இருந்தால்தான் எலக்ட்ரான் வெளிவரும். மீதி ஆற்றல் இயக்க ஆற்றலாகும்.
Key notes, relationships and model limits
Remember
A photon must supply the work function before an electron can escape. Its remaining energy is the maximum kinetic energy. Greater intensity increases emission rate above threshold, while greater frequency raises maximum electron energy.
Common trap
High intensity cannot overcome the threshold in the one-photon model.
Model limits
One-photon emission from an ideal surface; no multiphoton effects. Below threshold no emission. Relative intensity scales available electron count after emission, not Kmax.
What you will learn
Separate threshold, stopping potential and emission rate.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
At800 THz and φ2 eV, Kmax≈1.309 eV and Vs≈1.309 V.
Why this matters
The model connects photoelectric threshold with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Above threshold, increasing intensity alone changes Kmax how?
- It increases Kmax
- It leaves Kmax unchanged
- It makes Kmax negative
Read the explanation
Kmax=hν−φ depends on frequency and material.
Course connection: Class XII Chapter 11. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.