# Physics - AQA A - Electrical Current

Flashcards for Chapter 4

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• Created by: shayoni
• Created on: 03-12-12 17:22

## 4.1 Current and Charge

Electrical Conduction

For an Electrical current to pass around a circuit a circuit must be complete and there must be a source of potential difference. .

Electrical Current - Is the rate of flow of charge in the wire/component

Current is due to a passage of charged particles, (Charge Carriers)

*In metals, charge carrirs are conduction electrons. (They move about inside the metal repeatedly colliding with eachother and the fixed positive ions in the metal)

*When an Electrical current is passed through a salt solution the charge is carried by ions, which are charged atoms/molecules.

A Simple test for conduction of materials is connecting the material in a ciruit with a cell and a component such as a lightbulb. The cell forces the charge carriers through the conducting material and causes electrons to pass through the cell and the (in this case a lightbulb) lighbulb and the bulb lights up.

If the test Material is metal, electrons leave the cell at it's negative terminal, pass through the metal then re-enter the cell at it's positive terminal.

The direction for current is from Positive to negative (agreed before the discovery of electrons)

The unit of current is the Ampere (A) which is defined in terms of the magnetic force between two parallel wires when they carry the same current. The Symbol for current is I.

The unit of charge is the Coulomb (C), equal to the charge flow in one second when the current is One Ampere. The symbol for charge is Q.

Q= I x T

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## 4.1 Current and Charge (CONTINUED)

Materials can be classified (in electrical terms) as Insulators, Conductors or semiconductors.

*In a insulator, each electron is attatched to an atom and cannot move away from the atom. When Voltage is applied across an insulaotr

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