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When light shines on a metal plate, electrons can be ejected from the plate. An electron will be ejected if the energy, E, of a photon (particle of light) striking the plate is greater than the minimum energy, M, required for the electron to be removed from the plate. The maximum kinetic energy of the ejected electron, K, is the difference between E and M as shown in the equation: K = E − M Students conducted 2 experiments to examine how differences in the light striking a metal plate affect K. The setup included a light source, a removable filter, a circuit with an ammeter to measure current, a power supply that could be adjusted to measure K, and a vacuum tube containing a metal plate and an electrode (see Figure 1). Figure 1 filter light vacuum tube metal plate electrode electrons 19.8 mA power supply ammeter Experiment 1 A filter was placed between the metal plate and the light source, and the K of the ejected electrons was measured. This procedure was repeated with each of 4 additional filters. Each filter transmitted light of only one frequency. Table 1 lists the following: • color of light transmitted by the filter • frequency of light in hertz, Hz • E in electron volts, eV • K in electron volts Table 1 Frequency E K Color (× 10 Hz) (eV) (eV) Red 4.4 1.81 N.A.* Yellow 5.2 2.14 N.A.* Green 5.6 2.31 0.11 Blue 6.3 2.60 0.40 Violet 7.5 3.10 0.90 *N.A.—Not available; no electrons were ejected. Experiment 2 With the same setup as in Experiment 1 except without a filter, the current, in milliamperes (mA), and K were measured as the intensity of the light was varied. Table 2 shows the current and K for 4 different relative light intensities, each given as a percent of maximum intensity. Table 2 Relative Current K intensity (mA) (eV) 100% 40.0 0.90 50% 19.8 0.90 25% 9.8 0.90 12.5% 4.8 0.90