Refer to the figure at the right. You are designing a time delay system that wil
ID: 1411201 • Letter: R
Question
Refer to the figure at the right. You are designing a time delay system that will close an electrical circuit one minute after electrical power is applied to the timer. The timer is constructed out of a 4.0 cm long (at 20degree C) copper rod with a mass of 10 g that is fixed to a copper block at the left end, and has a gap of .010 cm between its right end and a second copper block. A heating coil is wrapped around the rod, and the heating coil is powered by a power supply. One minute after applying power to the heating coil, the rod will contact the right hand block, completing the circuit between the left and right hand blocks. At what copper rod temperature, in Celsius degrees, will the right end of the rod contact the right hand block, completing the circuit? How much energy, in Joules, must be supplied to the rod by the heating coil to reach the temperature calculated in , above? Assume all the energy produced by the heating coil goes into the rod. Recall from the week 5 lab experiment that Q = mcAT If the rod is to reach the temperature calculated in in one minute how much power, in Watts, must be produced by the heating coil?Explanation / Answer
a) L = L(Tf – Ti)
0.00010 = 0.004[16*10^-6(Tf – 20)] => Tf = 1582.5 C
b)Q = mcT = 0.010*800*(1582.5-20) = 12500 J
c)P= Q/t = 12500/60 = 208.33 W