Module 2: Series DC Circuits
Recap
Do you still recall
these?
Recap
• What are electric circuit components?
• Does the current flow in an open or close circuit?
• Give examples of five output devices
Outlines
• Series circuit • Current in a series circuit• Resistance in a series circuit• Voltage in a series circuit– Kirchhoff’s Voltage Law– Voltage divider circuit
• Power in a series circuit• Variable resistor • Trouble Shooting series circuit
Technical words and units
• Voltage across R• Voltage drop across R• Current through R• Power dissipated in R• Voltage: v• Current: A• Resistance: Ω• Power: W
Series circuit
• connecting of components end to end in a circuit to provide a single path for the current.
How many paths you have for the current?
Do you think it only applies for
resistors?
• It is common to connect input devices in series (power supplies)
• It is not common to connect loads in series.
Why ??
Applications of series circuits
Search the web for real examples of series circuit.
Exercise 1 page 4
• Using wires, connect all of the cells in series to create a 6V battery source. Then connect all of the lamps in series with the battery.
Solution of Exercise 1
What is the total voltage ?
Is this correct ?
Current in a Series Circuit
• A series circuit has only path for current to travel
• The current through a series circuit is the same
IT = I1 = I2 = I3
Resistance in a Series Circuit
• Resistance is the opposition to current flow
𝑅T = 1 + 2 + 3 + R4𝑅 𝑅 𝑅
Example1
• Calculate the total resistance of the circuit
Can be drawn as:
RT
• How many path exist for the current in the series circuit?
• What happen to the current in the series circuit?
• What happen to the resistance in the series circuit?
Ohm’s Law
• 𝑉 = ×𝐼 𝑅• Where V = voltage (Volts)• I = current (Amps)• R = resistance (Ohms)
Example
• Find the current.
Voltage in a Series Circuit
• The total voltage supplied by the power supply is divide among the loads
Kirchhoff’s Voltage Law
• total voltage in a series circuit is equal to the sum of the individual voltage drops in the circuit.
• 𝑉T= 1 + 2 + 3 …𝑉 𝑉 𝑉
Voltage Divider
• V1 = [R1/(R1+R2)]*V• V2 = [R2/(R1+R2)]*V
• V: Source voltage
Variable Voltage Divider
• Potentiometer is a variable resistor with three terminals.
Power is a series circuit
• Power’ is the measure of the energy consumed by a circuit.
• Unit: Watt• 𝑃 = ×𝐼 𝑉• 𝑃 = 𝐼2×𝑅• P = V2/R• 𝑃T = 1 + 2 + 3 …𝑃 𝑃 𝑃
Important Notes
• The resistance of the open component is huge
• The resistance of the short component is zero
• Open switch has huge resistance
• Close switch has zero resistance
Problems in a series circuit
Problems in series circuits
A component is open
a component’s value will change over a period of
time
A component is shorted
A component is open
• Lamp 3 is open
• The current is zero
• All the lamps are OFF,
• all voltage is dropped across Lamp3
• V1 = V3 = zero
A component is shorted
• Lamp 2 is short
• The current is not zero
• Lamp2 is OFF, Lamp 1 and 3 ON
• V2 = Zero
• V1 = V3 = 9/2 volts
LAB ACTIVITY 3
LAB ACTIVITY 3: Safety instructions
• Be quite
• Don’t switch ON the power supply till the teacher check the circuit for you
• Take the measurements quickly because the resistors will get very hot
LAB ACTIVITY 3, Stage-1:
• R1 = 820Ω• R2 = 470Ω
• V2calculated =• V2measured =
LAB ACTIVITY 3, Stage-2:
V2 V R1 R2 V2 measured
3 9 R2/2 R2
5 9 (5/4)R1 R2
LAB ACTIVITY 3, Stage-3:
Conclusion
• Current in series circuit• Resistance in the series circuit• Voltage in the series circuit• Power in the series circuit• Kirchhoff voltage law