Electric Current Alexandro Volta Ever since Volta first

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Electric Current

Electric Current

Alexandro Volta • Ever since Volta first produced a source of continuous current, men

Alexandro Volta • Ever since Volta first produced a source of continuous current, men of science have been forming theories on this subject. For some time they could see no real difference between the newly discovered phenomenon and the former understanding of static charges

Andre-Mari Ampere Then the famous French scientist Ampere (after whom the unit of current

Andre-Mari Ampere Then the famous French scientist Ampere (after whom the unit of current was named ) determined the difference between the current and the static charges. In addition to it, Ampere gave the current direction: he supposed the current to flow from the positive pole of the source round the circuit and back again to the negative pole.

Wrong Direction • We consider Ampere to be right in his first statement but

Wrong Direction • We consider Ampere to be right in his first statement but he was certainly wrong in the second, as to the direction of the current. The student is certain to remember that the flow of current is in a direction opposite to what he thought.

 • Electric current is the flow (movement) of electric charges. The unit of

• Electric current is the flow (movement) of electric charges. The unit of electric current is the ampere, and electric current is measured by using an ammeter.

Ampere • Current can be measured by a galvanometer, via the deflection of a

Ampere • Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current.

Ammeter • Standard ammeter • Zero-center ammeter

Ammeter • Standard ammeter • Zero-center ammeter

 • A solid conductive metal contains a large number of mobile, or free

• A solid conductive metal contains a large number of mobile, or free electrons. These electrons are bound to the metal lattice but not to any individual atom. Even with no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there is zero net current within the metal.

 • The current in amperes can be calculated with the following equation: I=d.

• The current in amperes can be calculated with the following equation: I=d. Q/dt • where Q-is the electric charge in coulombs (ampere seconds) t-is the time in seconds

The drift speed of electric charges • The mobile charged particles within a conductor

The drift speed of electric charges • The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas. In order for there to be a net flow of charge, the particles must also move together with an average drift rate. Electrons are the charge carriers in metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in the direction of the electric field.

Ohm's law • Ohm’s law predicts the current in an (ideal) resistor to be

Ohm's law • Ohm’s law predicts the current in an (ideal) resistor to be equal to the applied voltage divided by resistance: U=I*R

Conventional Current • Conventional current was defined early in the history of electrical science

Conventional Current • Conventional current was defined early in the history of electrical science as a flow of positive charge. In solid metals, like wires, the positive charge carriers are immobile, and only the negatively charged electrons flow.

 • The diagram shows conventional current flow. Electric charge moves from the positive

• The diagram shows conventional current flow. Electric charge moves from the positive side of the power source to the negative.

Alternating Current • An alternating current (AC) is an electrical current whose magnitude and

Alternating Current • An alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, and this results in the most efficient transmission of energy.

 • City lights viewed in a motion blurred exposure. The AC blinking causes

• City lights viewed in a motion blurred exposure. The AC blinking causes the lines to be dotted rather than continuous.

Direct current • Direct current is produced by such sources as batteries, thermocouples, solar

Direct current • Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be transmitted through semiconductors, insulators, or even through a vacuum. In direct current, the electric charges flow in the same direction, distinguishing it from alternating current (AC).

Types of DC

Types of DC

 • Electric current produces a magnetic field. The magnetic field can be visualized

• Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire. • Electric current can be directly measured with a galvanometer, but this method involves breaking the circuit and this is sometimes inconvenient.

THE END

THE END