Charge and mass can stand alone; a magnetic pole cannot
Which property gives an object a gravitational field?
The magnet refused to give up a lone pole. Do the other two field sources refuse the same way?
No. Charge and mass can each stand alone.
A sphere can carry only negative charge, with nothing else on it. That sphere is an electric monopole, and spheres like it sit on lab benches everywhere. A sphere carrying only positive charge exists just as easily.
The electric field first: a sphere carrying only negative charge stands alone.
Can a metal sphere carry only negative charge, with no other type on it?
Mass stands alone too. Mass comes in one type only, so any lone mass is a single-type source. A lone stone is a gravitational monopole.
Mass stands alone too: a lone stone is a single-type source.
The odd one out is the magnet: magnetic poles always come in pairs, so a magnetic monopole has never been found.
Two of the three fields have single-type sources; the magnetic field never does.
Which field's sources are never found as a single type?
Electric monopoles exist. Gravitational monopoles exist. Magnetic monopoles have never been found.
A metal ball on an insulating stand carries only positive charge. Does the ball show that electric monopoles exist?
The ball carries a single type of charge, standing alone.
A single-type source standing alone is a monopole.
Yes. The ball is an electric monopole.
A student says mass can stand alone as a single-type field source. Is the student correct?
Your turn
Which single-type source has never been found?
An asteroid drifts alone in space, carrying mass and no charge. Which description fits the asteroid as a field source?