W. Sautter 2007

AMPS

volts

Ammeters measure current in amperes and are always wired in series in the circuit.

Voltmeters measure potential in volts and are always wired in parallel in the circuit.

battery wiring voltmeter ammeter resistance capacitor +

V

A junction terminal AC generator Variable resistance Variable capacitor

ELECTRONS INTO LOAD LOAD (RESISTANCE) [ENERGY OUT] ELECTRONS OUT OF LOAD CONDUCTOR CONDUCTOR ELECTRONS OUT OF SOURCE HIGHER ENERGY ELECTRONS ELECTRON PUMP (SOURCE VOLTAGE) [ENERGY IN] ELECTRONS BACK TO SOURCE LOWER ENERGY ELECTRONS

Potential In volts (joules / coul) Drop across a resistance Current In amperes (coul / second) Current passing Through the resistor Resistance In ohms (volts / amp)

volts

current Electrons have More Energy Battery Electrons get An energy boost current Electrons have Less Energy

Electrons have Less Energy

volts

Resistor Energy is lost In the resistor current Electrons have More Energy

There are three generally types of electrical circuits: (1) Series circuits in which the current created by the voltage source passes through each circuit component in succession.

R 2 A R 1 1 A 2 R 3 Arrows show Current path Through each component

(2) Parallel circuits in which the current created by the voltage source branches with some passing through one component and while the rest of the current passes through other components.

R 1 A 1 R 2 A 2 Arrows show Current path Through each component R 3 A 3 R 4 Junction or Branching points A 4

P A R A L L E L R 4 R 1 R 2 R 3

SERIES

A 1 A 2 (3) Series Parallel circuits or combination circuits which contain series segments and parallel segments.

A 3 Arrows show Current path Through each component A 4

All electrical circuit analysis requires the use of two fundamental laws called Kirchhoff’s Laws

FIRST LAW All current entering a junction point must equal all current leaving that junction point

Current Leaving ( I 3 ) Current Leaving ( I 2 )

Junction point

I

1

= I

2

+ I

3 Current Entering ( I 1 )

SECOND LAW Around any complete loop, the sum of the voltage rises must equal the sum of voltage drops

Resistance 1 (voltage drop 1) Resistance 2 (voltage drop 2)

Current flow

Complete loop + Battery (voltage rise)

V

(Battery)

= V

1

+ V

2 -

+ V

3 Resistance 3 (voltage drop 3)

V 2 R 2 Loop #2 A 2 Loop #3 V 1 R 1 A 1 Loop #1 + EMF

-

A t Complete current Paths in a circuit



Kirchhoff’s Laws Around a loop V rises =



V drops A loop is a completed Path for current flow Battery

When using Kirchhoff’s laws we apply the principles of conventional current flow.

When current leaves the positive (+) terminal of a voltage source and enters the negative (-) terminal a voltage rise occurs across the source. If the current enters the positive and exits the negative a of a voltage source a voltage drop occurs across the source.

When tracing a current loop, if the assumed direction of the current and the loop direction are the same, a voltage drop occurs across a resistance.

If the assumed direction of the current and the loop direction are opposite, a voltage rise occurs across the the resistance.

When using Kirchhoff’s laws we apply the principles of conventional current flow.

When current leaves the positive (+) terminal of a voltage source and enters the negative (-) terminal a voltage rise occurs across the source. If the current enters the positive and exits the negative a of a voltage source a voltage drop occurs across the source.

Current flow V = - 6 v + Battery ( 6 volts) V = + 6 v Current flow

When tracing a current loop, if the assumed direction of the current and the loop direction are the same, a voltage drop occurs across a resistance.

If the assumed direction of the current and the loop direction are opposite, a voltage rise occurs across the the resistance.

Loop direction Assumed Current flow V = - 6 v A voltage drop resistor V = + 6 v A voltage rise Loop direction Assumed Current flow

In a series circuit: (1) The total resistance of the circuit is the sum of the resistance values in the circuit.

R t Series Resistance = R 1 + R 2 + ….

(

2) The sum of all voltage drops across the resistors in the circuit equals the voltage rise of the source.

EMF = V 1 + V 2 + V 3 + V i The through each resistance is the same.

I TOTAL = I 1 = I 2 = I 3 = I i

Voltmeters In parallel Ammeters In series A 1 V 2 R 2 V 1 R = Resistance In ohms R 1 A 2 R t Series Resistance = R 1 + R EMF = V 1 + V 2 2 + ….

+ V 3 + V i R i EMF R 3 V 3 Ammeters read The same everywhere In the circuit A 1 = A 2

In a parallel circuit: (1) The reciprocal of the total resistance of the circuit is the sum of the reciprocals of the resistance values in the circuit.

Parallel Resistance 1/R t = 1/R 1 + 1/R 2 ….

(

2) The sum of the voltage drops across the resistors in a branch of the circuit equals the voltage rise of the source.

V source = V 1 = V 2 = V 3 = V i (3) All current entering a junction = all current leaving the junction I TOTAL = I 1 + I 2 + I 3 + I i

Voltmeters In parallel Junction points R = Resistance In ohms V 1 R 1 V 2 R 2 V 3 R 3 A A 1 2 Ammeters In series Parallel Resistance 1/R t = 1/R 1 + 1/R 2 ….

EMF A 3 A 4 Kirchhoff’s Laws (1) All current entering A junction = all current Leaving the junction



(2) Around a loop V rises =



V drops Battery

P A R A L L E L V 4 R 4 V 1 R 1 V 2 R 2 V 3 R 3 A 1 EMF R i

SERIES

A 2 A 3 A 4 Parallel Resistance 1/R t = 1/R 1 + 1/R 2 ….

R t Series Resistance = R 1 + R 2 + ….

Kirchhoff’s Laws (1) All current entering A junction = all current Leaving the junction



(2) Around a loop V rises =



V drops

capacitors Integrated circuits resistors