Electric fields
Attraction and repulsion
Opposite (unlike) charges attractObjects that tend to move together because of a force between them attract each other. one another. Like charges repelObjects that tend to push apart because of a force between them repel each other. one another.
This is often demonstrated using plastic rods charged with a duster.
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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
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Field lines
All charged objects have an electric fieldArea surrounding an electric charge that may influence other charged particles. around them. This is similar to how magnets have a magnetic fieldArea surrounding a magnet that can exert a force on magnetic materials.. Electric field linesImaginary lines along which a positive charge would travel. 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.
One way to demonstrate electric fields is to sprinkle semolina onto castor oil. The particles of semolina line up in the fields generated by electrodeA conductor used to establish electrical contact with a circuit. The electrode attached to the negative terminal of a battery is called a negative electrode, or cathode. The electrode attached to the positive terminal of a battery is the positive electrode, or anode. attached to a Van de Graaff generator.