You have three metal samples that are tantalum (Ta), barium (Ba), and tungsten (W), but you don't know which is which. Metal A emits electrons in response to visible light; metals B and C require UV light. [In his explanation of the threshold frequency in the photoelectric field, Einstein reasoned that the absorbed photon must have a minimum energy to dislodge an electron from the metal surface. This energy is called the work function (φ) of that metal. The work functions are Ta (6.81 × 10−19 J), Ba (4.30 × 10−19 J), and W (7.16 × 10−19 J).]