Question

The threshold frequency for photo electric effect on sodium corresponds to a wavelength 5000 Å. Its work function is –

• A. 15 Joule
• B. 10 × 10^–19 Joule
• C. 4 × 10^–19 Joule
• D. None of these

Answer 1

Answer: (C)

4 × 10^–19 Joule

Answer 2

f = $\frac { \mathrm { hc } } { \lambda _ { 0 } }$

f = $\frac { 20 \times 10 ^ { - 26 } } { 5000 \times 10 ^ { - 10 } }$ = 4 × 10 ^–19 Joule