A loud speaker high up on a pole is radiating 100 watts of audio power uniformly

Question

A loud speaker high up on a pole is radiating 100 watts of audio power uniformly in all directions. a) What is the intensity of audio sound at a distance of 3 meters from the speaker. b) What is the decibel level for the sound. (Note that the threshold value 10 = 10^-12 watts per meter squared. II. A long solenoid of radius 1.5 cm and length 20 cm produces a magnetic field of 0.1 tesla at its center when carrying a current i = 3 amperes. a) How many turns N of wire does the solenoid have? b) The middle section of the solenoid is surrounded by a single loop of wire containing a resistance r = 5 ohms. If the current in the solenoid is increasing at the rate of 7 umperes per second, what is the current in the loop of wire? c) Is the induced current from u to b or from b to a in the figure?

Explanation / Answer

2) (II)According to the given problem,

a)For a solenoid B=µ0*N*I/L

Substitute the values to get N

N = B*L/µ0*I

N = 0.1 * 0.2/4* *10-7*3

N = 5305 turns

b)First we shall denote the rates of changes of magnetic flux density and current with dB/dt and dI/dt respectively.

dB/dt= n(dI/dt)
= (4.00 x10-7)(5305)(7)
= 0.0466T/s

Now, The magnetic flux of a solenoid,
= BAcos, where B is the magnetic flux density, A is the cross sectional area of the solenoid and is angle between the normal to the cross section and the magnetic field lines, which is 0° in this case.
The induced emf across one of the windings,
= the rate of change of magnetic flux(d/dt)
= A(dB/dt)
= (7.068x10-4)(0.0466)
= 3.29 *10-5V

Then the current in the loop of wire is I = V/R

I = 3.29 * 10-5/5

I = 6.658 * 10-6 A

c) the induced is current is from b to a in the figure

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.