Photoelectric cut-off voltage , Vo = 1.5VK.E = eVwhere e = charge of an electron = 1.6 × 10⁻¹⁹ Cso, K.E = 1.6 × 10⁻¹⁹ × 1.5K.E = 2.4 × 10⁻¹⁹ J