Module 2 Series DC Circuits Recap Do you

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 6 V 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 = I 1 = I 2 = I 3

Resistance in a Series Circuit • Resistance is the opposition to current flow �� T = �� 1 + �� 2 + �� 3 + R 4

Example 1 • 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 resistance in the series circuit?

Ohm’s Law • �� = �� ×�� • 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. • �� T= �� 1 + �� 2 + �� 3…

Voltage Divider • V 1 = [R 1/(R 1+R 2)]*V • V 2 = [R 2/(R 1+R 2)]*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 • �� = �� ×�� 2×�� • �� = �� • P = V 2/R • �� T = �� 1 + �� 2 + �� 3…

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 Lamp 3 • V 1 = V 3 = zero

A component is shorted • Lamp 2 is short • The current is not zero • Lamp 2 is OFF, Lamp 1 and 3 ON • V 2 = Zero • V 1 = V 3 = 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: • R 1 = 820Ω • R 2 = 470Ω • V 2 calculated = • V 2 measured =

LAB ACTIVITY 3, Stage-2: V 2 V R 1 R 2 3 9 R 2/2 R 2 5 9 (5/4)R 1 R 2 V 2 measured

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