Chapter 5- Ohm’s Law Landstown High School Governors STEM & Technology Academy

Electric circuits – The path that the current follows is called an electric circuit. – All electric circuits consist of: A voltage source. A load. A conductor. 2

Three types of circuits – Series circuit 3

– Parallel circuit 4

– Series-parallel circuit 5

Closed circuit 6 Open circuit Open and Closed Circuits

Current flow can be varied by: – Changing the voltage applied to the circuit. Voltage increases, current increases. Voltage decreases, current decreases. – Changing the resistance in the circuit. Resistance increases, current decreases. 7

OHM’S LAW The current in an electrical circuit is directly proportional to the voltage and inversely proportional to the resistance in a circuit. 8

9 I = current in amperes. E = voltage in volts. R = resistance in ohms. Finding the Current (I) Value

10 E= I x R I = current in amperes. E = voltage in volts. R = resistance in ohms. Finding the Voltage (E) Value

11 R = E/I I = current in amperes. E = voltage in volts. R = resistance in ohms. Finding the Resistance (R) Value

In a series circuit, the same current flows throughout the circuit. I T = I R1 = I R2 = I R3... = I Rn The total voltage in a series circuit is equal to the voltage drop across the individual loads in the circuit. E T = E R1 + E R2 + E R E Rn 12 Rules

3 Formulas E = I x R (Voltage = Current multiplied by Resistance) R = E / I (Resistance = Voltage divided by Current) I = E / R (Current = Voltage Divided by Resistance) 13

The total resistance in a series circuit is equal to the sum to the individual resistances in the circuit. R T = R 1 + R 2 + R R n 14

In a parallel circuit, the same voltage is applied to each branch in the circuit. E T = E R1 = E R2 = E R3... = E Rn The total current in a parallel circuit is equal to the sum of the individual branch currents in the circuit. I T = I R1 + I R2 + I R I Rn 15

To determine unknown quantities in a circuit: – Draw a schematic of the circuit. – Label all known quantities. – Solve for equivalent circuits. – Redraw the circuit. – Solve. 16

Kirchhoff’s Law – In 1847 G. R. Kirchhoff extended Ohm’s law with two important statements. – Kirchhoff’s current law: The algebraic sum of all the currents (I) entering and leaving a junction is equal to zero. I T = I 1 + I 2 + I 3 17 – Kirchhoff’s voltage law The algebraic sum of all the voltages (E) around a closed circuit equals zero. E T = E 1 + E 2 + E 3

In summary: – Electric circuit Voltage source Load Conductor – Current path Series Parallel Series-parallel 18 – Current flow Negative to positive Varied by changing the voltage or the resistance.

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