Photoelectric emission is observed from a surface for frequencies v1 and v2 of the incident radiation (v1>v2). If the maximum kinetic energies of the photoelectrons in the two cases are in the ratio 1:k then the threshold frequency v0 is given by:
O v2−v1/k−1
O kv2−v1/k−1
O v2−v1/k
O kv1−v2/k−1