# MHS Physics Department AP Unit III C 2 Steady state direct current circuits with batteries and resistors only.

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MHS Physics Department AP Unit III C 2 Steady state direct current circuits with batteries and resistors only

MHS Physics Department a) Students should understand the behavior of series and parallel combinations of resistors, so they can: (1) Identify on a circuit diagram whether resistors are in series or parallel. (2) Determine the ratio of the voltages across resistors connected in series or the ratio the currents through resistors connected in parallel. (3) Calculate the equivalent resistance of a network of resistors that can be broken down into series and parallel combinations.

MHS Physics Department (4) Calculate the voltage, current, and power dissipation for any resistor in such a network of resistors connected to a single power supply. (5) Design a simple series-parallel circuit that produces a given current through and potential difference across one specified component and draw a diagram for the circuit using conventional symbols

MHS Physics Department (b) Students should understand the properties of ideal and real batteries, so they can: (1) Calculate the terminal voltage of a battery of specified emf and internal resistance from which a known current is flowing. (2) Calculate the rate at which a battery supplying energy to a circuit or is being charged up by a circuit.

MHS Physics Department (c) Students should be able to apply Ohm’s Law and Kirchoff’s rules to direct current circuits in order to: (1) Determine a single unknown current, voltage, or resistance. (d) Students should understand the properties of voltmeters and ammeters, so they can: (1) State whether the resistance of each is high or low. (2) Identify or show correct methods of connecting meters into circuits in order to measure voltage or current

MHS Physics Department Series Circuits The resistance in a series circuit is equal to the sum of the resistances around the circuit. R T = R 1 +R 2 + R 3 R1R1 R2R2 R3R3

MHS Physics Department Parallel Circuits The total resistance an a parallel circuit is from the inverses of the individual resistances 1/ R T = 1/R 1 + 1/R 2 + 1/R 3 R1R1 R2R2 R3R3

MHS Physics Department If a series circuit has 3 resistors each of 15 Ω, calculate the total resistance in the circuit. If a parallel circuit has 3 resistors each of 15 Ω, calculate the total resistance in the circuit. Three resistors in parallel, 15 Ω, 25 Ω, 35 Ω. Calculate the total resistance in the circuit.

MHS Physics Department Kirchoff’s Laws First Law: At a junction the total current entering the junction is equal to the total current leaving the junction Second law: The net e.m.f. (electromotive force) around a circuit loop is equal to the sum of the p.d.’s around the loop.

MHS Physics Department Voltmeters Voltmeters are connected in parallel ACROSS the component they are measuring the potential difference of. They have a high internal resistance so negligible current goes through them. V

MHS Physics Department Ammeters Have low resistance and measure the current going THROUGH the circuit so must be connected in SERIES with the components. A

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