# Charge and current relationship

### The Open Door Web Site : IB Physics : THE RELATION BETWEEN CURRENT, CHARGE AND TIME

An electric current is a flow of electric charge In electric circuits this charge is often carried by The relationship between the voltage (V), resistance (R), and current (I) is V=IR; this is known as Ohm's law. Common symbols. I. SI unit · ampere. Charge, Current & Potential Difference. Circuit Symbols – you met these circuit symbols in GCSE Physics. circuit symbols. Conventional current flows around a. Once the Voltage at the terminals of the Capacitor, v c, is equal to the Power Supply Voltage, vc= V, the Capacitor is fully charged and the Current stops flowing.

In many contexts the direction of the current in electric circuits is taken as the direction of positive charge flow, the direction opposite to the actual electron drift.

## Electric current

When so defined the current is called conventional current. Current is usually denoted by the symbol I. The relationship between current and resistance in an electric circuit. Current in gases and liquids generally consists of a flow of positive ions in one direction together with a flow of negative ions in the opposite direction. To treat the overall effect of the current, its direction is usually taken to be that of the positive charge carrier.

The slow progress of the colour makes the current visible.

Circuits: Current and Charge Graph Analysis

Since the electrical conductivity is low, gases are dielectrics or insulators. However, once the applied electric field approaches the breakdown value, free electrons become sufficiently accelerated by the electric field to create additional free electrons by colliding, and ionizingneutral gas atoms or molecules in a process called avalanche breakdown.

The breakdown process forms a plasma that contains enough mobile electrons and positive ions to make it an electrical conductor. In the process, it forms a light emitting conductive path, such as a sparkarc or lightning. Plasma is the state of matter where some of the electrons in a gas are stripped or "ionized" from their molecules or atoms.

A plasma can be formed by high temperatureor by application of a high electric or alternating magnetic field as noted above.

Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than the heavier positive ions, and hence carry the bulk of the current. However, metal electrode surfaces can cause a region of the vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission.

Thermionic emission occurs when the thermal energy exceeds the metal's work functionwhile field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunnelingwhich results in the ejection of free electrons from the metal into the vacuum.

Externally heated electrodes are often used to generate an electron cloud as in the filament or indirectly heated cathode of vacuum tubes. Cold electrodes can also spontaneously produce electron clouds via thermionic emission when small incandescent regions called cathode spots or anode spots are formed.

### Charge, Current & Potential Difference

These are incandescent regions of the electrode surface that are created by a localized high current. These regions may be initiated by field electron emissionbut are then sustained by localized thermionic emission once a vacuum arc forms. These small electron-emitting regions can form quite rapidly, even explosively, on a metal surface subjected to a high electrical field. The conducting material has a large number of free electrons.

When the voltage or emf is applied across the free electron, it starts moving and induces the current. The electric current is of two type i. In alternating current, the charges move in both the direction.