Question

In an experiment tungsten cathode which has a threshold wavelength 2300 Å is irradiated by ultraviolet light of wavelength 1800 Å. The maximum energy of emitted photo-electron will be –

• A. 1.2 eV
• B. 1.5 eV
• C. 1.6 eV
• D. 1.8 eV

Answer 1

Answer: (B)

1.5 eV

Answer 2

K_max = hc $\left( \frac { 1 } { \lambda } - \frac { 1 } { \lambda _ { 0 } } \right)$

= $\frac { 6.62 \times 10 ^ { - 34 } \times 3 \times 10 ^ { 8 } } { 1.6 \times 10 ^ { - 19 } }$ $\left( \frac { 10 ^ { 10 } } { 1800 } - \frac { 10 ^ { 10 } } { 2300 } \right)$

= 1.5 eV