Electric Charge

• There are 2 types of charges: positive and negative.

• Unlike charges attract and like charges repel.

• The SI unit of charge is the Coulomb (C).

• The presence of an electrostatic charge can be detected using a leaf electroscope.

  • If a charged object is placed near the cap, charges are induced.

  • The metal cap gets one type of charge (positive or negative) and the metal stem and gold leaf get the other type of charge so they repel each other.

• Electric field: region in which electric charge experiences a force.

• The direction of an electric field at a point is the direction of the force on a positive charge at that point

• Conductors: materials that let electrons pass through them. Metals are the best electrical conductors as they have free electrons. E.g. copper

• Insulators: materials that hardly conduct at all. Their electrons are tightly held to atoms and hardly move, but they can be transferred by rubbing. E.g. Rubber

• Simple Field Patterns:

Parallel plates	Point charge	+ve and -ve	+ve and +ve

• Induced charges:

  • Charging a body involves the addition or removal of electrons.

  • A charge that "appears" on an uncharged object because of a charged object nearby

  • For example if a positively charged rod is brought near a small piece of aluminum foil, electrons in foil are pulled towards rod, which leaves the bottom of the foil with a net positive charge.

  • The attraction is stronger than repulsion because the attracting charges are closer than the repelling ones.

Current#

• Current: a flow of charge, the SI unit is the Ampere (A).

• An ammeter measures the current in a circuit and is connected in series

• Current is a rate of flow of charge.

• In metals, current is caused by a flow of electrons

• Current follows path of least resistance

• Conventional current flows in the direction opposite to that which electrons flow in.

• Red = Conventional Current

• Green = flow of electrons