A thermocouple has an e.m.f. of 5 mV when the hot junction is at 100 °C and the cold junction is at 0 °C. A thermopile consisting of 25 such thermocouples in series is used as a detector in a chopped, broadband pyrometer. When unchopped the power in the beam of radiation incident on the hot junction of the thermopile is given by 7.5T 4 pW, where T K is the temperature of the distant target. The beam is chopped by a semicircular disc rotating at 6000 r.p.m. The reference junction of the thermopile is at the temperature of the pyrometer

enclosure. Assuming the thermocouples are linear and the detector data given below, sketch the form of the output signal when T = 2000 K.