hand rules (1 Viewer)

[hollyy.]

does anyone have a summary of the hand rules we need to know for m&g?
like which hand? what points to what etc? the textbooks are confusing me

 

[dolbinau]

Right hand grip rule = conventional current in a conductor. Thumb points direction of conventional current, fingers point direction of magnetic field.

Right hand palm rule = Conventional current for questions relating to Motor Torque, Eddy Currents/Lenz Law, charged particles in magnetic field. Fingers point direction of magnetic field, palm points direction of force, thumb points direction of conventional current.

For real current, or electrons in magnetic field, use other hand or change direction of current with right hand palm rule.

I suppose there are other situations each one is used, but if you've got no idea I'm sure this is a start.

 

[helper]

There are a number of versions that do the same thing. Which you learn is dependent on which you are confident with.

The answer from dolbinau is the simplest as it keeps the same meaning for everything and you don't need to change hands. You just need to remember to point your thumb in the other direction for negative charges.

 

[azn-drew]

I think it'd be funny to be a co-ordinator for a physics exam watching all the students play around with their hands during a test. =]
irrelevent i know...but still. ^^

 

[xds123]

IMPORTANT most people dont actually realise that if you use the right hand rule for motors to work out the direction of induced current in a generator or anything you will violate Lenzs law and thus get it wrong

you need to use flemmings right hand generator rule

point thumb up, forefinger forward (like a pretend gun) and middle finger toward the left.

now T humb represents T hrust
F orefinger is F ield
and se C ond finger is induced C urrent

 

[helper]

IMPORTANT most people dont actually realise that if you use the right hand rule for motors to work out the direction of induced current in a generator or anything you will violate Lenzs law and thus get it wrong

you need to use flemmings right hand generator rule

You can use it but you need to understand how to use it. You don't need to change the hand rule.

 

[hollyy.]

IMPORTANT most people dont actually realise that if you use the right hand rule for motors to work out the direction of induced current in a generator or anything you will violate Lenzs law and thus get it wrong

you need to use flemmings right hand generator rule

point thumb up, forefinger forward (like a pretend gun) and middle finger toward the left.

now T humb represents T hrust
F orefinger is F ield
and se C ond finger is induced C urrent

my teacher taught that i think FBI he called it. i never got it. i think ill go with what dolbinau said.

 

[dolbinau]

You can use it but you need to understand how to use it. You don't need to change the hand rule.

Yes..for generator I use the right hand palm rule in direction of motion then just swap current direction so to oppose it. (The induced current)

 

[helper]

Yes..for generator I use the right hand palm rule in direction of motion then just swap current direction so to oppose it. (The induced current)

I prefer saying the force is going to stop the motion, so the palm pushes against the direction of motion. The thumb then points in the direction of the induced current.

For some induced currents, you are better off using the right hand grip rule. Eg. Loops expanding and contracting or being moved in and out of magnetic fields.

 

[me121]

There are a number of versions that do the same thing. Which you learn is dependent on which you are confident with.

The answer from dolbinau is the simplest as it keeps the same meaning for everything and you don't need to change hands. You just need to remember to point your thumb in the other direction for negative charges.

i very much agree with this.

 

[dolbinau]

I prefer saying the force is going to stop the motion, so the palm pushes against the direction of motion. The thumb then points in the direction of the induced current.

For some induced currents, you are better off using the right hand grip rule. Eg. Loops expanding and contracting or being moved in and out of magnetic fields.

Do you know where there is an example of these?

 

[helper]

Of which, the first or the second statement?

 

[dolbinau]

The second

 

[helper]

If you look at the picture below

What direction would the induced current be if the size of the ring expanded to 15 cm?

Increasing size increases flux, so you want to decrease the flux. Grip ring so, you fingers are coming out of page (oppose flux). So current is counter clockwise.

2.

As the coil enters the field its flux increases, so grip coil, so fingers are pointing out, opposing change. Current counter clockwise. The opposite occurs as it leaves.

 

[xds123]

current runs anticlockwise

 

[Shoom]

So is the end of my thumb were the positive particles will be meaning the bottom of my thumb is the hegavtive charged placed?