past hsc paper question (1 Viewer)

[rama_v]

Hey guys I got a quick question
Question 21 of HSC 2004
(a) The diagram shows a two-pole DC motor as constructed by a student.
Identify THREE mistakes in the construction of this DC motor as shown in the
diagram.

http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2004exams/pdf_doc/physics_04.pdf

I can only think of two - the commutator should be made from graphite, adn teh coild do not have current flowing through them as they are not attached to the armature from what I can see. Can anyone please tell me the other mistake in teh construction of this motor?

 

[lilkatie]

well
1 theres no electrical connection between the ends of the wire and the split ring commutator
2. The windings of the coil are wound anticlockwise on one side of the axle and clockwise on the other side hence would produce forces in opp direction
3. the split ring commutator is incorrectly placed on the axle and would need to rotate through 90* in order to work
hope that helps , pretty sure it's right =)

 

[BlackJack]

I concur on the above 3 points.... that motor's not going anywhere... why the hell did he wind 2 sets of coils counterphase?

 

[rama_v]

Thanks for the help, I get it.

 

[thunderdax]

Also, the brushes are made of copper instead of carbon, meaning a lot of friction

 

[m_isk]

well
2. The windings of the coil are wound anticlockwise on one side of the axle and clockwise on the other side hence would produce forces in opp direction

forces on opposite ends of the rotor in opposite directions=rotation