force and torque in motors?

[nfreidman]

in a motor with a split ring commutator, is it correct to say that the magnitude of the force on the coil is constant (because of F=BILsintheta) and sintheta is always equal to 1, but the direction of the force changes. Also, is it correct to say that the magnitude of the torque changes because this depends on the cos of the angle between the coil's plane and the magnetic field lines but the direction of the torque remains constant (always either clockwise or anti clockwise)?

also, are torque and force both vector quantities?

thank you

 

[nightweaver066]

The magnitude of the force acting to move the coil is NOT constant as it varies according to theta.

The only constant values in, F= BILsin(theta) are B and I (supposing you're not changing those). (theta) constantly changes as the coils rotate in the magnetic field.

The direction of the force on the coil is the same at all points, i.e. F = BIL.

The force acting to turn the coil can be found using vectors such that F = BILsin(theta).

Yes it is correct to say that the magnitude of the torque changes depending on the angle between the plane of the coil and the magnetic flux and the direction remains constant.

 

[Timothy6340]

The magnitude of the force acting to move the coil is NOT constant as it varies according to theta.

The only constant values in, F= BILsin(theta) are B and I (supposing you're not changing those). (theta) constantly changes as the coils rotate in the magnetic field.

The direction of the force on the coil is the same at all points, i.e. F = BIL.

The force acting to turn the coil can be found using vectors such that F = BILsin(theta).

Yes it is correct to say that the magnitude of the torque changes depending on the angle between the plane of the coil and the magnetic flux and the direction remains constant (only with split-ring commutator).

thelast part is aslo correct for slit ring communicators as the coil still continues to rotate in the same direction but the direction of the voltage changes due to the slit ring

 

[nightweaver066]

thelast part is aslo correct for slit ring communicators as the coil still continues to rotate in the same direction but the direction of the voltage changes due to the slit ring

You mean slip rings? True, i forgot about AC motors haha.

 

[Timothy6340]

yea thats what i meant slip not stil lol

 

[Kimyia]

thelast part is aslo correct for slit ring communicators as the coil still continues to rotate in the same direction but the direction of the voltage changes due to the slit ring

?

 

[teeah]

?

commutator?

 

[rolpsy]

The magnitude of the force acting to move the coil is NOT constant as it varies according to theta.

The only constant values in, F= BILsin(theta) are B and I (supposing you're not changing those). (theta) constantly changes as the coils rotate in the magnetic field.

Aren't the sides of the coil always perpendicular to the magnetic field?

 

[scarvesss]

commutator?

split ring for DC motors kind of looks like "--( )--"

and slip ring for AC

 

[scarvesss]

Aren't the sides of the coil always perpendicular to the magnetic field?

in a radial magnetic field yes. but not in a normal one. you should know this man its simple.

 

[rolpsy]

in a radial magnetic field yes. but not in a normal one. you should know this man its simple.

are you sure?

think about it – if you look at it from the top with magnets on either side the coil would shrink from a rectange into a line, still remaining perpendicular to the magnetic field

 

[Rathaen]

are you sure?

think about it – if you look at it from the top with magnets on either side the coil would shrink from a rectange into a line, still remaining perpendicular to the magnetic field

The force on the coil is constant from F=BILsin(theta) because the sides of a square coil will be perpendicular to the magnetic field (with magnets on either side).

The torque, however will be different, because the force on each side of the coil changes distance relative to the pivot point of the coil as it rotates, (since torque=force x distance).
In a radial magnetic field, torque remains constant.