The Electric Field Concept

The Electric Field Concept

As children grow, they become very accustomed to contact forces; but an action-at-a-distance force upon first observation is quite surprising. Seeing two charged balloons repel from a distance or two magnets attract from a distance raises the eyebrow of a child and maybe even causes a chuckle or a "wow." Indeed, an action-at-a-distance or non-contact force is quite unusual. Football players don't run down the field and encounter collision forces from five yards apart. The rear-end collision at a stop sign is not characterized by repulsive forces which act upon the colliding cars at a spatial separation of 10 meters. And (with the exception modern WWF wrestling matches) the fist of one fighter does not act from 12 inches away to cause the forehead of a second fighter to be knocked backwards. Contact forces are quite usual and customary to us. Explaining a contact force which we all feel and experience on a daily basis is not difficult. Non-contact forces require a more difficult explanation. After all, how can one balloon reach across space and pull a second balloon towards it or push it away? The best explanation to this question involves the introduction of the concept of electric field.

Action-at-a-distance forces are sometimes referred to as field forces. The concept of a field force is utilized by scientists to explain this rather unusual force phenomenon that occurs in the absence of physical contact. While all masses attract when held some distance apart, charges can either repel or attract when held some distance apart. An alternative to describing this action-at-a-distance affect is to simply suggest that there is something rather strange about the space surrounding a charged object. Any other charged object that is in that space feels the affect of the charge. A charged object creates an electric field - an alteration of the space in the region which surrounds it. Other charges in that field would feel the unusual alteration of the space. Whether a charged object enters that space or not, the electric field exists. Space is altered by the presence of a charged object. Other objects in that space experience the strange and mysterious qualities of the space.

The strangeness of the space surrounding a charged object is often experienced first hand by the use of a Van de Graaff generator. A Van de Graaff generator is a large conducting sphere which acquires a charge as electrons are scuffed off of a rotating belt as it moves past sharp elongated prongs inside the sphere. The buildup of static charge on the Van de Graaff generator is much greater than that on a balloon rubbed with animal fur or an aluminum plate charged by induction. On a dry day, the buildup of charge becomes so great that it can exert influences on charged balloons held some distance away. If you were to walk near a Van de Graaff generator and hold out your hand, you might even notice the hairs on your hand standing up. And if you were to slowly walk near a Van de Graaff generator, your eyebrows might begin to feel quite staticy. The Van de Graaff generator, like any charged object, alters the space surrounding it. Other charged objects entering the space feel the strangeness of that space. Electric forces are exerted upon those charged objects when they enter that space. The Van de Graaff generator is said to create an electric field in the space surrounding it.