Question from Jacaranda 2 book (Motors n generators) (1 Viewer)

[elfanger]

Pg 128 Jacaranda 2 HSC book question 20.

I read the question a few times and do not realy undertand what to do. Explanations would be helpful.

Question 22 part a. I do not understand question.
part b. i used formula torque=nBIAcos(pheta)

n=1 B=0.025T I=1.5A A=0.027m^2 (pheta)=45

After subbing into formula and solving i got Torque = 7.2x10^-4

The book had a totaly different answer. Help plz.

 

[Ragerunner]

You made sure you got the units for the area right?

I would help if i had the book, but library got pissed after I borrowed it for over 8 months.

 

[+:: $i[Q]u3 ::+]

lol @ ragerunner.. hehehe.. i have a yr9 book for english i still havent' returned...

q20 - remember the motor effect? --> current-carrying conductor in a magnetic field will experience a force.
using right-hand rule...
fingers in direction b-field (leftways)
u know how u have the two wires? the first one.. the current is coming AT you, so u stick ur thumb towards u..
the palm faces down yeah? so the force on A is downwards.

similarly, the current at B is going AWAY from u - stick ur thumb taht way, fingers still leftways, and palm is upwards..
so the force is upwards.

it's the same deal for any dc motor.

22a - same as q20 - use right hand rule.
22b - the question asks for the force, not torque. F = BILsin(theta)

oh btw.. n= 50.. (read the question - 50 loops)

hope that helps - =)

 

[elfanger]

Helped alot. Thanks!

For question 22a) The curent is going up the coil AB the field direction is left i cannot work out force i cant twist my hand into such a weird position. What is the adirection? I got the other questions right.

 

[+:: $i[Q]u3 ::+]

just remember - sometimes the drawing'll look a bit odd cuz it's like 3D.

And also - forget about what orientation the coil is in (ie if it's flat or at an angle etc). Pretend that the coil does not exist - you're only looking at the individual wire AB. (AB is perpendicular to the B-field remember)

So thumb towards B, fingers to the left, and the palm (the force) is upwards. It's drawn a bit odd... but yeah.
the force is up, so the coil will turn right. is dat okay? =)

 

[elfanger]

Cool thanks. i figured it out. Its the 3d that was annoying me. I got used to it now.