The heating coils in a hair dryer are 0.800 cm in diameter, have a combined leng
ID: 1512513 • Letter: T
Question
The heating coils in a hair dryer are 0.800 cm in diameter, have a combined length of 1.00 m, and a total of 395 turns. What is their total self-inductance assuming they act like a single solenoid? How much energy is stored in them when 11.9 A flows? What average emf opposes shutting them off if this is done in 4.17 ms (one fourth of a cycle for 60 Hz AC)? Suppose that these coils have an internal resistance of 7.13 0. What is the RL time constant for the hair dry How much time is needed for the coils to reach 99.9% of full current when they are turned on?Explanation / Answer
a)
r = 0.4 cm = 4*10^-3 m
A = pi*r^2
= pi*(4*10^-3)^2
= 5.03*10^-5 m^2
L = miuo*N^2*A/L
L = (1.2566*10^-6)*(395)^2 * 5.03*10^-5 / 1
= 9.9*10^-6 H
Answer: 9.9*10^-6 H
b)
E = 0.5*L*I^2
= 0.5*(9.9*10^-6)*(11.9)^2
= 6.98*10^-4 J
Answer: 6.98*10^-4 J
c)
E= -L*dt/dt
= -9.9*10^-6 * 11.9 / (4.17*10^-3)
= -0.028 V
Answer: 0.028 V
d)
time constant = L/R
= (9.9*10^-6)/7.13
=1.4*10^-6 s
Answer: 1.4*10^-6 s
I am allowed to answer only 4 parts at a time
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