दिया है --- ` lamda = 488 nm, V_0 = 0*38 V`
सूत्र -- `1/2 mv_("max")^(2) = hv - phi_v`
या `eV_0 = (hc)/lamda - phi_0`
या `phi_0 = (hc)/lamda - eV_0`
या ` phi_0 =(66xx10^(-34)xx 3 xx10^(8))/(488 xx 10^(-9)) - 1*6 xx 10^(-19)xx 0*38`
`= 4*057 xx 10^(-19) - 0*608 xx 10^(-19)`
` = 3*449xx 10^(-19)`
` = 3*449 xx 10^(-19)J`
`= 3*449 eV`.