about directions (1 Viewer)

[1234567]

can some one sort of restate all the LHR, RH PUSH RULE, RH PALM RULE thingy?
and also .... how do u determined teh direction current in solenoid when a magnet is moved towards/away from the solenoid?
+ what about the direction of the induced current?

i am stuffed.

 

[Dumbarse]

for the solenoid, the end of the solenoid will try and resist the magnet coming towards it so will be the same pole as whatever pole is at the end which is going into the solenoid
if u know what pole end the solenoid is , then using right hand grip ruile, with your thmb as the north end and the direction your fingers wrap around is the direction of the induced current

sorry for the crap explanation

 

[Jellymonsta]

LHR = Fleming's Left Hand Rule
ie F, B, and I are going to be perpendicular.
Thumb - force direction
First finger - magnetic field direction
Second finger - Current direction
Line up the two known vectors, and read the unknown vector direction.
There are different ways to do it, but this is the one i was taught.

 

[1234567]

oh yeah....
start to remember now...

 

[Jellymonsta]

but how could you forgot this stuff? its so important
i was thinking of just tatooing all the formulas and rules to my arms and forehead, but im too scrawny and my head is not large enough. actually, its not very large at all...

 

[1234567]

well i still remeber one more

but ........ the real thing is i forgt how to apply it in order to find al the direction stuff..esp the solenoid ones....sux

 

[Dumbarse]

solenoids are the easiest bit in motors and generators

eddy currents and back emf, now that stuff sux

 

[1234567]

oh yeah...
can someone demonstrate how the rules can be applied to eddy current and back emf???????
please.......

 

[BlackJack]

I use the right hand palm rule, but there's no need to confuse you...

Let's use the DC motor...
Current going up one side:
Motor effect (mag fld into screen):
Side moves left:
But side moving left is moving charge in mag field:
Motor effect:
back emf generated downwards, opposing the generating current.

continued for eddy c.

 

[BlackJack]

Let's use eddy current in a train wheel...

Wheel is spinning clockwise. But, we're looking at the bottom of the wheel, which is constantly moving left:
Magnetic field applied into page:
Motor effect (I should've said before use the BFI rulesl right hand palm or that left hand thingy):
Conventional current moves down (i.e. electrons move up):
Potential difference generated:
Electrons flow back down the side of the field to even the PD out (outside the magnetic field):
Voila, cycle of eddy current.

 

[Dumbarse]

"Voila, cycle of eddy currents"

well which way did the eddy currents end up going and why. sorry i couldnt understand the end of your explaining

 

[BlackJack]

Wait a minute... now that you ask... eddy current direction is measured by the directions of the flow of positive charge right? That is actually down.
So the eddy current goes DOWN through the mag. field and back UP the side.

If someone has a Jacaranda, flip to the part on electromagnetic braking. It has a diagram there which should tell definitively.