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circuits-old - DC Circuits Objective: To learn how to build...

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DC Circuits Objective: To learn how to build and run an electrical circuit. To measure current and voltage anywhere in the circuit. To determine the relationships between Current, Voltage and Resistance. To learn Kirchoff's Rules Apparatus: SnapCircuits board, circuit elements, cables, DC power supply, multimeter (combination voltmeter/ammeter/ohmmeter), light bulb ( 6V limit – do not exceed for a single bulb in series ). Introduction So far our labs have focused on electrical fields that have macroscopic effects – a charged rod that attracts bits of paper or foil, two charged copper spheres or scotch tape strips that attract or repel each other. Now we will examine the microscopic effects of electrical fields in wires that conduct electricity. You will build simple circuits and learn to measure Voltage, Current and Resistance (both directly and from the slope of V vs. I. Theory The following summarizes what you have have already learned in lecture about circuits: Electric Potential The electric field E is related to the rate of change of electric potential V. If the electric potential changes by the amount V , the electric field in the direction of the displacement is:
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E =− V s Current Current I is defined as the flow of charge Q per until time: I = Q t Power Power P is the rate of energy flow per unit time through a circuit or circuit element: P = VI = I 2 R Ohm's Law For many a material, the current I through it is proportional to the potential difference across it, with the resistance R being the constant of proportionality, as well as the slope of the V vs. I graph: V = IR Materials that behave this law are known as ohmic materials; those that do not are non-ohmic. The power that is dissipated through a resistor also obeys Kirchoff's Junction Rule The current entering any point in a circuit must equal the current leaving that point. This ensures that there is no charge buildup anywhere, which would violate conservation of charge and energy: A junction is where roads or paths meet or connect. In the junction on the right, the current I 1 splits up into I 2 and I 3 . So that there is no excess buildup of charge or current in the circuit, this condition must be fulfilled: I 1 = I 2 + I 3 . or I 1 - I 2 - I 3 = 0 Kirchoff's Loop Rule The algebraic sum of all potential differences around any closed loop in a circuit is zero:
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circuits-old - DC Circuits Objective: To learn how to build...

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