The graph shows variation of stopping potential V0 with the frequency of the incident radiation for three photosensitive metals X1, X2 and X3. Which metal will give out electrons with greater kinetic energy, for the same wavelength of incident radiation? [figure]
- X1
- X2
- X3
- All the metals will give out photoelectrons with same kinetic energies.
Answer
(1) X1
Solution
[figure]
Einstein's photoelectric equation: K =eV0=h -h 0
⇒ V0= he( - 0): all three lines have the same slope he; the intercept on the -axis is the threshold frequency 0.
Same wavelength ⇒ same for all three metals (dashed line).
∴ K is largest for the metal with the smallest 0 (smallest work function).
0: X1=1.0 1014 Hz < X2=1.5 1014 Hz < X3=2.0 1014 Hz
∴ X1 emits electrons with the greatest kinetic energy.
Answer: (1)