help with physic problem (1 Viewer)

[red802]

uh i got a problem, in this picture, how can it do a 360 movement, because once it goes 180 degrees, wouldnt the force push it back.

View attachment 12326

also another question

1)calculate the maximum torque on a sqaure coil with 200 turns, saides 1-cm, carrying current of 2.5A in a 0.6T magnetic field

2)Calculate the minimum torque on this coil

 

[sasquatch]

The motor is able to completely rotate 360 degrees, by using a component called a "commutator" which consists of a split metal ring, which changes the direction of the current when the torque reaches 0. This is when the motor completes a 90 degree rotation (you said 180, but i think you meant 90). At this point, the direction of the current changes, and hence the forces change direction, completing another 180 degree rotation. This process is repeated again so that the motor is able to completely rotate 360 degrees.



1) t = n BIA cos @

The maximum torque is given when the the coil makes an angle of zero with the magnetic field (cos 0 being 1)

A = (0.01)²
= 0.0001 m²

t = 200 * (0.6)(2.5)(0.0001) cos1
= 0.03 N m

2)Calculate the minimum torque on this coil

2) The minimum torque is given when the coil makes an angle of 90 degrees with the magnetic field

t = n BIA cos 90
t = 0 Nm


Edit: Fixed something i left out in the image.
Edit 2: Fixed problem identified in post somewhere below.

 

[red802]

sry about, just one more question, why does the torque decraese as its roates from parallel to perpendicular to the field, apart from the fact of cos90 equal minimum force

 

[sasquatch]

Im pretty sure its because of this:

When the motor rotates to this 90 degree angle, the forces then act directly opposite to each other. Even though the coil always has a net force of zero, when the forces are applied at a distance to each other from the centre of rotation, the turning effect (or torque) causes the rotation of the coil. So at the point where the coil is 90 degrees to the magnetic field, the forces act directly opposite, and have the same magnitude, in which no turning force (torque) acts.

 

[red802]

thank u

 

[sasquatch]

No problem. Hope you understood me though...

 

[Riviet]

The motor is able to completely rotate 360 degrees, by using a component called a "commutator" which consists of a split metal ring, which changes the direction of the current when the torque reaches 0. This is when the motor completes a 90 degree rotation (you said 180, but i think you meant 90). At this point, the direction of the current changes, and hence the forces change direction, completing another 90 degree rotation. This process is repeated again so that the motor is able to completely rotate 360 degrees.

Red082 was actually right, just replace everything you said for 90 with 180 degrees.
If you are unsure of why, draw a diagram and work it out.

 

[sasquatch]

Oh nuh i think i only got the second angle wrong. The motor starts off parallel to the magnetic field, then moves 90 degrees where the torque reduces to zero. From THERE it completes 180 degrees, until the torque reaches zero. Yeah and this is right because the angle starts of at zero to the magnetic field (cos 0 = 1) at 90 degrees (cos 90 = 0) and it states that the communator changes the direction of the current when the torque reaches zero. Then from there it completes another 90 degree rotatation (180 degrees, cos 180 = -1, the torque is still not zero), then another 90 degrees until the current changes again (cos 270 = 0), the moves back to where it starts.

So to correct my post it should be:

The motor is able to completely rotate 360 degrees, by using a component called a "commutator" which consists of a split metal ring, which changes the direction of the current when the torque reaches 0. This is when the motor completes a 90 degree rotation (you said 180, but i think you meant 90). At this point, the direction of the current changes, and hence the forces change direction, completing another 180 degree rotation. This process is repeated again so that the motor is able to completely rotate 360 degrees.

 

[Quynh nhu]

Does anyone have access to the 2005 HSC physics exam paper plus the solutions? Qu 17/ Einstein’s 1905 theory of special relativity made several predictions that could not be verified for many years. I chose “relativity of time”.
c) Explain how technological advances since 1905 have made it possible to carry out this experiment.

 

[Mountain.Dew]

Does anyone have access to the 2005 HSC physics exam paper plus the solutions? Qu 17/ Einstein’s 1905 theory of special relativity made several predictions that could not be verified for many years. I chose “relativity of time”.
c) Explain how technological advances since 1905 have made it possible to carry out this experiment.

uhh i think ur talking about time dilation, am i not mistaken?

for this question, you really need to do some research beforehand to answer that question.

technological advances includes such things like quartz clocks and atomic clocks that are extremely accurate in measuring time, for very very tiny amounts of time, perhaps by nanoseconds or even less. this enabled scientists to be able to detect minor differences in the travel time for muons as they fall to earth from space, this relates to time dilation.

there are many other things to consider. what i described was somewhat a little inaccurate, but its a starting point.

SMALL NOTE: in future please post questions on einstein's relativity in the "Space" sub-forums please, not in Motors and Generators.

 

[Quynh nhu]

hey, thanks

 

[Mountain.Dew]

a pleasure, a pleasure