Electric fields

All charged objects have an electric field around them, which shows how they will interact with other charged particles.

A radial magnetic field is shown by equally-spaced arrows arranged in a circle around a positive point charge, pointing out.A radial field around a positive charge

A Van de Graaff generator removes electrons to produce a positive charge. A person does not have to touch the Van de Graaff generator to start feeling the effects, as static electricity is a non-contact force. This force will act on any charged particle in the electric field around the generator.

A person touching the dome of the Van de Graaff generator will also lose electrons and become positively charged. The same will happen to each of their hairs. Since the person, their head, and each of the hair follicles are all positively charged, the hairs will repel from the head and from every other strand causing them to stick out from the head in all directions.

Electric field shapes

An electric field is a region where charges experience a force.

Fields are usually shown as diagrams with arrows:

  • The direction of the arrow shows the way a positive charge will be pushed.
  • The closer together the arrows are, the stronger the field and the greater the force experienced by charges in that field. This means that the field is stronger closer to the object.
A bar magnet, with several curved lines pointing from the north to south pole
curriculum-key-fact
Field lines point away from positive charges and towards negative charges.

With a radial field around a positive charge, other positive charges are repelled away. Therefore, the arrows are pointing away from the central positive charge. This is what happens with the example of the Van de Graaff generator.

However, if a negative charge is placed in that field, it would attract the positive charge and feel a force in the opposite direction to the field lines.

A uniform magnetic field is shown by arrows pointing from a positively charged plate to a negatively charged plate.

The field between two parallel plates, one positive and the other negative, would be a uniform field.

The field lines would be straight, parallel and point from positive to negative.

If the field is strong enough, charges can be forced though insulators such as air and a spark will occur. This is what happens during a lightning strike. It may also happen if a charged person touches a conductor. For example, a person dragging their feet across the carpet may become charged, so if they reach out to touch a door handle there is a spark and they feel a small shock.

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