Electronics_Review

Electronics_Review - Review of Basic Electronics Author:...

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Review of Basic Electronics Author: John M. Cimbala, Penn State University Latest revision: 29 February 2008 Introduction Electronic circuits are critical components in most laboratory instruments. In this learning module, we review the basics of electronic circuits; we use this material throughout the rest of the course. Resistance A resistor impedes the flow of both DC and AC currents. V 1 R V 2 I The schematic diagram for a resistor is shown to the right, where R is the resistance in ohms ( Ω ), Δ V = V 1 - V 2 is the voltage drop across the resistor in volts (V), and I is the current flowing through the resistor in amperes (A). Note : Sometimes we use E instead of V for voltage (or electric potential ); E and V are used interchangeably. The definition of ohm is as follows: A one- Ω (ohm) resistor with one V (volt) across it has a current of one A (ampere) flowing through it , or V 1 A Ω= . Expressed as a unity conversion ratio, 1 1 V/A Ω ⎛⎞ = ⎜⎟ ⎝⎠ . The current through a resistor and the voltage drop across a resistor change instantaneously with time. At any instant in time, Ohm’s law holds: VI R Δ = . Ohm’s law is valid for both DC and AC signals; time is not a factor in circuits that contain only resistors . Resistors in series (as sketched to the right): V 1 R N V 2 I N R 1 I 1 R 2 I 2 o The total resistance for resistors in series is total 1 2 ... N R RR R =+++ , and 12 ... N II I I = === . o For resistors in series, the current is the same through each resistor, but the voltage drop may differ across each individual resistor. Resistors in parallel (as sketched to the right): o The total resistance for resistors in parallel is total 1 11 1 ... N R R = ++ + , and total 1 2 ... N II I V 1 V 2 I total R 1 I 1 R N I N R 2 I 2 I . o For resistors in parallel, the voltage drop is the same across each resistor, but the current through each individual resistor may differ. As a simple example of a useful circuit containing only resistors, consider a voltage divider , as sketched to the right. V in R 2 R 1 V out o The symbol on the left of the circuit represents a battery or some other DC voltage supply that provides the input voltage V in . o The output voltage V out is smaller than the input voltage V in by a linear ratio between the resistances, 2 out in R VV R R = + . Capacitance A capacitor stores an electrical charge, and blocks DC current.
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Electronics_Review - Review of Basic Electronics Author:...

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