# MSU PHY 252 - Ohms Law (17 pages)

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## Ohms Law

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- Pages:
- 17
- School:
- Michigan State University
- Course:
- Phy 252 - Intro Physics Lab II

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EXPERIMENT 1 Ohm s Law Objectives Become familiar with the use of a digital voltmeter and a digital ammeter to measure DC voltage and current Construct a circuit using resistors wires and a breadboard from a circuit diagram Construct series and parallel circuits Test the validity of Ohm s law Reduce a complicated resistance circuit to a simple one resistor equivalent circuit Note If you are color blind or suspect that you are you may find the color codes on the resistors difficult Please consult your lab instructor for advice or help Introduction One of the fundamental laws describing how electrical circuits behave is Ohm s law According to Ohm s law there is a linear relationship between the voltage drop across a circuit element and the current flowing through it Therefore the resistance R is viewed as a constant independent of the voltage and the current In equation form Ohm s law is V I R Here 1 V voltage applied across the circuit and has SI units of volts V I current flowing through the circuit and has SI units of amperes A R resistance of the circuit and has SI units of ohms Equation 1 implies that for a resistor with constant resistance the current flowing through it is proportional to the voltage across it If the voltage is held constant then the current is inversely proportional to the resistance If the voltage polarity is reversed that is if applied voltage is negative instead of positive the same current flows but in the opposite direction If Ohm s law is valid it can be used to define resistance as R V I Where R is a constant independent of V and I It is important to understand just what is meant by these quantities The current I is a measure of how many electrons are flowing past a give point during a set amount of time The current flows because of the electrical potential V sometimes referred to as the voltage applied to a circuit In much the same way that a gravitational potential will cause mass to move electrical potential will cause electrons to

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