While demonstrating Faraday\'s law to her class, a physics professor inadvertent
ID: 1434145 • Letter: W
Question
While demonstrating Faraday's law to her class, a physics professor inadvertently moves the gold ring on her finger from a location where a 0.81 Tmagnetic field points along her finger to a zero-field location in 46 ms . The 1.6 cm -diameter ring has a resistance and mass of 51 and 16 g , respectively.
A) Estimate the thermal energy produced in the ring due to the flow of the induced current. Q = mJ
B) Find the temperature rise of the ring, assuming all of the thermal energy produced goes into increasing the ring's temperature. The specific heat of gold is 129 J/kgC. T = C
Explanation / Answer
B1 = 0.81 T, B2 =0 , d =1.6 cm , r =0.8 cm , t =46 ms
R =51 , m = 16g
(A) from faradya law induced emf V = -d(phi)/dt = A(B1-B2)/t
V = (3.14*0.8*0.8*10^-4*0.81)/(0.046)
V =0.00354 V
Power P =Q/t =V^2/R
Q = (V^2*t)/R = (0.00354*0.00354*0.046)/(51*10^-6)
Q = 11.3 mJ
(B) Cp =129 J/kg oC
Q = mCpT
0.0113 = (0.016)*129T
T = 0.0055 oC
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