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Static and charge - OCR GatewayElectric fields

Electric current is caused by moving electric charges. The effects of charge and electric fields can be investigated by looking at the forces they exert on conductors and insulators.

Part of Physics (Single Science)Electricity

Electric fields

Attraction and repulsion

Opposite (unlike) charges one another. Like charges one another.

Large red circle contains 鈥+鈥 symbol and smaller blue circle contains 鈥-鈥 symbol. Two arrows between the particles, point inwards towards each other.
Two blue circles contain 鈥-鈥 symbol. Two arrows between the particles point outwards away from each other.

This is often demonstrated using plastic rods charged with a duster.

Image gallerySkip image gallerySlide 1 of 2, A metal bar lying horizontally is suspended from string. It is adjacent to vertical metal bar. Both bars carry same charge. Bar on the string is repelled by the other, and swings away from it., Two identical plastic rods have like charges. The hanging rod turns away from the other rod.

Demonstrating charge

The only way to tell if an object is charged is to see if it repels another charged object. This is because a charged object can attract an uncharged insulator.

For example, a negatively charged plastic object such as a comb or ruler repels electrons in a piece of paper. The near side of the paper to the plastic object becomes positively charged, so it is attracted to the plastic object. This is why party balloons attract hair after they have been rubbed on a shirt or jumper.

Learn more on electric fields in this podcast

Field lines

All charged objects have an around them. This is similar to how magnets have a . Electric are not visible, but their effects are.

Any object with an electric charge will feel a force if it is in an electric field. It is not necessary for the charged objects to touch for the electric field to have an effect. Electric field lines are shown as:

  • leaving a positively charged object in all directions
  • entering a negatively charged object
  • closest where the field strength is greatest

The diagram shows how opposite charges are attracted to one another.

Opposite charges

One way to demonstrate electric fields is to sprinkle semolina onto castor oil. The particles of semolina line up in the fields generated by attached to a Van de Graaff generator.