Asst 10

course phy122

This was a short asst. Tried to skip problem 3 (said Univ. physics) and it seemed to end.Exam 1 next. Got your message about better self-critique. You can safely assume the better the self-critique the better the understanding I have of the concepts being tuaght (and vice verca.) A poor self critique is not me being lazy. I am working daily with my tutor as I just need a quicker turn around time this week to have a hope of passing the exam. Self critiques will be better for parts 2,3, and 4 provided I am able to get that far.

assignment #010

I'm obligated to nag a little about the self-critique process, but I know that it's not possible to do everything as thoroughly as we could if we had time. The main goal is to learn the material well enough to perform on the tests and do the labs.

010. `Query 31

Physics II

07-31-2007

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15:30:06

Query Principles and General Physics 21.04. A circular loop of diameter 9.6 cm in a 1.10 T field perpendicular to the plane of the loop; loop is removed in .15 s. What is the induced EMF?

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RESPONSE -->

d=9.6 cm = 9.6*10^-2m

B=1.1T

t=0.15s

k'=10^-7 Tesla/(amp meter)

B=(2k' Pi I) / a

I=(Ba)/(2k'pi)

V=4 * A * E * f

EMF V=4 pi r^2 B * (1/t) r=9.6 * 10^-6=0.096/2

V=(4 pi * (0.048)^2 * 1.1 * 1) / 0.15

V=(4 pi (0.048)^2 * 1.1)/ 0.15 = 0.21V

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15:30:36

The average induced emf is the average rate of change of the magnetic flux with respect to clock time. The initial magnetic flux through this loop is {}{}flux = magnetic field * area = 1.10 T * (pi * .048 m)^2 = .00796 T m^2.{}{}The flux is reduced to 0 when the loop is removed from the field, so the change in flux has magnitude .0080 T m^2. The rate of change of

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RESPONSE -->

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15:36:58

flux is therefore .0080 T m^2 / (.15 sec) = .053 T m^2 / sec = .053 volts.

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RESPONSE -->

4 was for sphere. since it is a loop (circufrence) I should of multiplied by 1.10 instead of 4.

(1.1 * pi * (0.048^2) * 1.1)/0.15=.058V (pi as 3.14)

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15:44:24

query gen problem 21.23 320-loop square coil 21 cm on a side, .65 T mag field. How fast to produce peak 120-v output?

How many cycles per second are required to produce a 120-volt output, and how did you get your result?

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RESPONSE -->

320 loop square coil

21cm

Area=0.21m

V=A*B*f

f=V/(AB) = 120/((0.21)^2 * 65)

f=120/(320*(0.21)^2*65

=0.13/sec

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17:46:16

The average magnitude of the output is peak output/sqrt(2) . We find the average output as ave rate of flux change.

The area of a single coil is (21 cm)^2 = (.21 m)^2 and the magnetic field is .65 Tesla; there are 320 coils. When the plane of the coil is perpendicular to the field we get the maximum flux of

fluxMax = .65 T * (.21 m)^2 * 320 = 19.2 T m^2.

The flux will decrease to zero in 1/4 cycle. Letting t_cycle stand for the time of a complete cycle we have

ave magnitude of field = magnitude of change in flux / change in t = 9.17T m^2 / (1/4 t_cycle) = 36.7 T m^2 / t_cycle.

If peak output is 120 volts the ave voltage is 120 V / sqrt(2) so we have

36.7 T m^2 / t_cycle = 120 V / sqrt(2).

We easily solve for t_cycle to obtain t_cycle = 36.7 T m^2 / (120 V / sqrt(2) ) = .432 second.+

A purely symbolic solution uses

maximum flux = n * B * A

average voltage = V_peak / sqrt(2), where V_peak is the peak voltage

giving us

ave rate of change of flux = average voltage so that

n B * A / (1/4 t_cycle) = V_peak / sqrt(2), which we solve for t_cycle to get

t_cycle = 4 n B A * sqrt(2) / V_peak = 4 * 320 * .65 T * (.21 m)^2 * sqrt(2) / (120 V) = .432 second.

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RESPONSE -->

We chose F as 1/t and it should be 1/4t.

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Good work. Let me know if you have questions. &#