Are you talking about the "v-block" on the base of a simple magnetic indicator stand?
To me "v-block" can mean anything from a method of centering cylindrical objects to holding barrels into stocks to a stock car motor to ???????
If you're asking how does the switch "turn off the magnet" in an indicator base....... it doesn't. It simply rotates a small cam which moves the magnet away from the metal bars in the base of the stand.
Magnetism is funny stuff, like light (and a bunch of other things like gravity) the force of magnetism diminishes at an "inverse square ratio" to distance, in other words if you double the distance from the object it's attracted to it loses traction at a rate corresponding to the the square of the distance. Magnetism also "conducts" through steel a little way, which is why a v-block can have the magnet 'way up inside.
What you and I can take from this is that you don't have to remove a magnet very far from a surface to make it virtually "lose" it's attractive impulse......this is how a magnetic release or "off switch" works. No circuitry, no 'lectronics, just simple application if the laws of physics. A little lever moves the magnet less than 1/4 inch and voilahhhh! no more sticky.
On the flip side, I've got a honkin' blood blister on my middle finger from fiddling with rare earth magnets making a tool holder for my lathe..... as quickly as they LOSE attraction, they also gain it!
Lesson of the day, when carrying a wicked strong magnet in each hand DON'T EVEN TRY TO PICK STUFF UP!!! Just walk on until the magnets are properly handed off
If you're talking about something else entire..... forgive me.
And if you're talking about an electromagnet then, here again, no circuitry..... cut the power to an electromagnet with a simple switch and the magnet "loses all it's pull."
al
