Download Chapter 5- Ohm`s Law

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.
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• Three types of circuits
– Series circuit
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– Parallel circuit
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– Series-parallel circuit
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Open and Closed Circuits
• Closed circuit
• Open circuit
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• 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.
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• OHM’S LAW
The current in an electrical circuit is directly
proportional to the voltage and inversely
proportional to the resistance in a circuit.
Current 
Voltage
Resistance
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Finding the Current (I) Value
E
I
R
I = current in amperes.
E = voltage in volts.
R = resistance in ohms.
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Finding the Voltage (E) Value
E= I x R
I = current in amperes.
E = voltage in volts.
R = resistance in ohms.
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Finding the Resistance (R) Value
R = E/I
I = current in amperes.
E = voltage in volts.
R = resistance in ohms.
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Rules
• In a series circuit, the same current flows
throughout the circuit.
IT = IR1 = IR2 = IR3 . . . = IRn
• The total voltage in a series circuit is equal to
the voltage drop across the individual loads in
the circuit.
ET = ER1 + ER2 + ER3 . . . + ERn
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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)
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• The total resistance in a series circuit is equal
to the sum to the individual resistances in the
circuit.
RT = R1 + R2 + R3 . . . +Rn
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• In a parallel circuit, the same voltage is applied to
each branch in the circuit.
ET = ER1 = ER2 = ER3 . . . = ERn
• The total current in a parallel circuit is equal to the
sum of the individual branch currents in the circuit.
IT = IR1 + IR2 + IR3 . . . + IRn
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• 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.
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• 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.
• IT = I1 + I2 + I3
– Kirchhoff’s voltage law
• The algebraic sum of all the voltages (E) around a
closed circuit equals zero.
• ET = E1 + E2 + E3
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• In summary:
– Electric circuit
• Voltage source
• Load
• Conductor
– Current flow
• Negative to positive
• Varied by changing the
voltage or the resistance.
– Current path
• Series
• Parallel
• Series-parallel
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