# Homework Help: Any help most appreciated

1. Aug 1, 2005

### brenton

hey, i have a physics quiestion which i am stuck on any help would be much appreciated

you are asked to design a generator to produce the same 50Hz, 240V(rms) as found in a domestic voltage outlet

The generator is made of a single flat coilbeing made to rotate in a uniform magnetic field of strength 0.08T. the coil may be of any surface area and have as many turns as you like, provided the area and number are "reasonable" values. the length of the coil is L, its width is W, and it spins at an angular rate (omega)w = 2Pi.50 rads/s

What values would you choose for thr area of the coil, A, and for the number of turns, N, that will provide this emf.

i have never done physics before so i dont even no what to begin...could comeone please run me though how i would attempt it..
thankyou

i no u dont do the problems for me but could u give me a formula i might be able to use or any pointers on how to begin this

2. Aug 1, 2005

### geosonel

an AC electric generator uses electromagnetic induction in a coil (rotating in a magnetic field) which is described by Faraday's Law. briefly, the changing magnetic flux thru a coil being rotated in a magnetic filed induces an AC voltage in the coil. the magnetic flux thru the coil is constantly changing because the coil is constantly rotating in the magnetic field, thereby producing (or "inducing") a continuous AC voltage.

the peak AC voltage produced is described by Faraday's Law:
Peak AC Voltage Magnitude = N*B*A*ω
where N is the number of coil turns, B the magnetic field, A the coil crossection area, and ω the angular rotation rate (in radians/sec).

since your problem requires the "RMS" AC Voltage, we divide the above formula by √2=1.414:
RMS AC Voltage Magnitude = N*B*A*ω/1.414

now place the problem's known values into the above equation and solve for (N*A) since the latter will provide your "design" parameters:
(240 volts) = N*(0.08 T)*A*(2*π*50 rads/s)/1.414
(N*A) = (1.414)*(240)/(0.08*2*π*50) = X ??? calculate this numerical value

compute the value of X in the above formula.

then to complete the problem, design your generator coil by choosing reasonable values for the number of coil turns (N) and coil crossection area (A in square meters) such that (N*A)=X from the above formula.

Last edited: Aug 1, 2005