Скачать или смотреть 17.1 Current and Ohm's Law | General Physics

Chad provides an introduction to Electric Current and Ohm's Law. Current is first defined as the flow of charge over time with the SI unit being the Ampere (Amp for short). Conventional current is also defined as the flow of positive charges over time (even though the actual current in a conductor involves the flow of electrons).

Ohm's Law is then presented and is one of the most important laws in all of General Physics 2: Delta V=IR. Ohm's law states that the potential drop across a resistor is directly proportional to the electric current and the resistance. It also provides a definition for resistance, the ratio of the potential difference to the electrical current and has the SI unit of Ohms. Three equivalent expressions for the power dissipated by a resistor are also presented and are then used along with Ohm's law to calculate the potential drop across a resistor and the power dissipated by the resistor.

The next part of the lesson reveals that the resistance of a wire is proportional to a property of the material the wire is composed of called resistivity. The resistance of the wire is also proportional to the length of the wire and inversely proportional to its cross-sectional area. A practice problem involving this relationship is solved.

Next, Chad provides the formulas for the temperature dependence of the resistivity and resistance which involve the temperature coefficient of resistivity. He performs a sample calculation demonstrating that conductors have higher resistance (i.e. are less conductive) at higher temperatures.

The lesson is concluded with a brief description of semiconductors which have virtually zero resistance, albeit usually only at very low temperatures.

00:00 Lesson Introduction
00:47 Definition of Electric Current (and Conventional Current)
03:19 Ohm's Law
04:34 Power Dissipated by a Resistor
09:29 Resistivity and Resistance
16:12 Temperature Dependence of Resistivity and Resistance
19:46 Superconductors

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