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