## Introduction |

## Teaching Aims |

## Atomic Nature of Electricity |

The polarity of the |

## Structure of the Atom |

An atom is the smallest particle of an element possessing the unique characteristics of that element. Atoms have a planetary type of structure. They consist of a central The nucleus consists of positively charged protons and |

## Valence Electrons |

Electrons orbit the nucleus at certain distances from the nucleus. Each orbit corresponds to a certain energy level. The electrons in the outermost orbit are called If a valence electron acquires a sufficient amount of energy, it can escape from the outer orbit. The escaped valence electron is called a |

## Categories of Materials |

When electrons can move easily from atom to atom in a material, it is |

## Electric Chargen |

Electricity is a physical phenomenon arising from the existence and interaction of electric charges.The The electric charge has either |

## Electric Field |

The ability of an electric charge to attract or repel another charge is actually a physical force. The larger the charge, the greater the electric force. This force is called The electrical field between oppositely charged surfaces and the electric field around a stationary charge are illustrated as examples. |

## Voltage (Potential Difference) |

Any charge has the potential energy to move another charge by either attraction or repulsion. The difference in the potential energy of two charges that move a certain number of electrons from one point to another is called Voltage is expressed as energy |

## Voltage Sources |

A |

## Current |

Free electrons are available in all conductive and semi conductive materials. These electrons drift randomly in all directions within the material, as shown in the figure. When a voltage is applied across the material, electrons start flowing from the negative to the positive side. Voltage is the |

## Current Value |

Current is measured by the number of electrons (having a charge, Q) that flow through the specific area per unit of time t. The unit of current is the The current indicates the |

## Resistance |

When a current is present, the free electrons move through the material and occasionally collide with atoms. Because of these collisions, electrons lose some energy and their movement is restricted. The property of the material that restricts the flow of current is called |

## Resistors |

A |

## Resistor Color Code |

Fixed resistors are color-coded to indicate their resistance value in ohms. The four-band The first three bands indicate the |

## Variable Resistors |

A |

## Potentiometer & Rheostat |

A A |

## Electric Circuit |

An Each circuit normally is represented by an associated |

## Current Direction |

The According to this convention, the electron current has the same direction even though electrons themselves move in the opposite way. Direct current has just |

## Closed and Open Circuit |

In a |

## Play & Learn a Simple Circuit |

Add and remove the connecting plugs from the bridging points by clicking between these points. Observe when the circuit is open or closed and see when the lamp is lit and when it is not. Note that the plugs 2 to 3 and 4 to 5 are connected in "series" i.e. one after the other in the circuit, whereas plugs 4 to 5 and 6 to 7 are connected in "parallel", i.e. with equivalent ends connected to the same conductor. |

## Basic Circuit Measurement |

A A |

## Current Measurement |

To measure current through the resistor, the circuit must first be opened - by removing the connecting plug from the bridging points. The DMM must be set as an ammeter - the round function switch should be in the Connect the ammeter into the current path with polarity as shown - negative-to-negative, positive-to-positive. Otherwise, the ammeter readings will be negative (indicated by a minus sign). Such a connection is a |

## Voltage Measurement |

Voltage is always measured relative to some other point in a circuit. Set the DMM as a voltmeter - the round function switch points to the The negative terminal of the meter must be connected to the negative side of the circuit, and the positive terminal of the meter to the positive side of the circuit. Otherwise the voltmeter readings will be negative. |

## Circuit Ground |

In the wiring of practical circuits, one side of the voltage source is usually grounded. For electronic equipment, the ground just indicates a metal chassis or a large conductive area on a printed circuit board, which is used as a All voltages in a circuit are referenced to ground unless otherwise specified. The figure gives a simple illustration of a grounded circuit and the ground symbol. |

## Voltage Measured to Ground |

Voltage measurements made at a single point in a circuit are made relative to the earth ( When voltages are measured with respect to ground, one of the meter leads is connected to the circuit ground, and the other to the point at which the voltage is to be measured. This is illustrated in the figure for several points in the circuit. |

## Resistance Measurement |

To measure resistance, set the function switch on the DMM to ohms.(Ω). This way the DMM functions as an ohmmeter. The resistor must first be disconnected from the circuit - remove the connecting plugs from the bridging points. Then the ohmmeter is connected across the resistor. Polarity is not important. Remember that infinite ohms mean an open circuit. In an open circuit the resistance is high but current is zero. |

## Simple Circuit Arrangement |

Arrange a simple circuit consisting of a voltage source and a resistor. Connect the ammeter and the voltmeter in the proper place in the circuit to measure current and voltage across the resistor. |

## Ohm's Law |

Ohm's law is one of the most important laws in the field of electricity and electronics. It gives the relationship between voltage, current and resistance in a circuit. According to Ohm's law, voltage and current are linearly proportional. When applied voltage increases, the current also increases if the resistance in a circuit is constant. |

## Ohm's Law (Continued) |

Ohm's law states that current varies directly with voltage and inversely with resistance. When the resistance increases, the current decreases in value if the applied voltage is constant. |

## Equivalent Form of Ohm's Law |

Ohm's law can also be stated in another way. From The circle diagrams in the figure provide a graphic aid for applying Ohm's law. It is a an easy way to remember the formulas. |

## Play & Learn a Volt-Ampere Characteristic |

The Ohm's law formula states that If R. To change the resistor's value click on the blinking star. Observe the slope of the graph for different resistors' values. _{3} |

## Power in an Electric Circuit |

When there is a current through a resistor, heat is produced by the collision of electrons and atoms. The heat is evidence that energy is used in producing current. The power The electric power in watts is the product of volts and amperes. By using Ohm's law, equivalent expressions are derived. The three power formulas are also known as |

## Power Rating of Resistors |

The |

## Series Circuit |

In a Components connected in series form a string - an end of each component is connected to an end of the next. |

## Total Series Resistor |

The _{1} + R_{2} + R_{3} + ... + R _{n} The U is the voltage applied across the total resistance. _{T} |

## Voltage Source in Series |

The The series voltage sources are added when their polarities are in the same direction and are subtracted when their polarities are in opposite direction. |

## Series Voltage Drop |

The The voltage drop across any of series resistors can be found from I is the series current. Using the meter's readouts for current and voltage drops, determine the resistance value of each resistor. |

## Kirchoff's Voltage Law |

The sum of all the voltage drops around a closed path in a circuit is equal to the total source voltage. The figure illustrates a verification of Kirchoff's voltage law. |

## Play & Learn Kirchoff's Voltage Law |

Measure the |

## Voltage Dividers |

A series circuit acts as a The voltage drop across any resistor in a series circuit is equal to the ratio of that resistance value to the total resistance, multiplied by the source voltage. The voltage divider is used for setting the DC operating point (bias) in an amplifier. |

## Play & Learn Voltage Dividers |

Calculate the voltage drop across each resistor using the voltage divider formula. Compare the calculated values with the measured ones. |

## Troubleshooting - Open Circuit |

When a series circuit is open, all of the |

## Troubleshooting - Short Circuit |

When there is a short, all of the current goes through the short. A portion of the series resistances is bypassed thus reducing the total resistances. As a result, the current increases. In order to troubleshoot a short, the voltage across each resistor can be measured until a reading of 0V is found. |

## Parallel Circuit |

When two or more resistors are individually connected between the same two points, they are The |

## Kirchoff's Current Law |

A The figure illustrates a verification of Kirchoff's current law. The total current is equal to the sum of all branch currents. |

## Total Parallel Resistance |

For convenience, parallel resistors are designated by two parallel marks. For example, R can be written as _{2}R_{1} || R_{2}. The total resistance R is determined by the reciprocal formula. It is applied to any number of parallel resistors in any value. In case of _{T}n equal resistors with resistance R, R. The total resistance of two resistors in parallel is equal to the product of the two resistors divided by the their sum. The _{T} = R/nR of a parallel circuit is always less than the value of the smallest resistor. _{T} |

## Application Assignment |

Determine the resistance value of the |

## Current Divider |

A parallel circuit acts as a The branch currents are |

## Troubleshooting - Open Branches |

The To find an "open", the total current I is always _{T}less than its normal value. If one of the resistors is open, the total current will equal the sum of currents in the good resistors. |

## Troubleshooting -Shorted Branches |

A short circuit across a branch shorts out all the branches. There is no voltage across the shorted branches. Since there is The short-circuited components are not damaged, however, because there is no current. The circuit draws excessive current from the source because of the short circuit. To protect the wiring and the voltage source from damage, there should be a fuse in the circuit that opens with excessive current. The components can operate again when the circuit is restored to normal by removing the short circuit. |

## Series-Parallel Circuits |

A |

## Analysis of Series-Parallel Circuit |

R_{1}+ R_{2} || R_{3}· R _{T} = R_{1} + R_{23}, where R_{23} = R_{2}·R_{3}/( R_{2}+ R_{3}). Total current I. The _{T} = U/ R_{T}voltage drops across resistors can be calculated using the voltage-divider principles. U_{R1} = U· (R_{1}/ R), _{T}U_{R2} = U· (R_{23}/ R). Voltages across _{T}R_{2} and R_{3} are equal because R_{2} || R_{3}. Branch currents are: I_{2} = U_{R2} / R_{2}; I_{3} = U_{R2} / R_{3}. Compare calculated values with the measured ones. |

## Other Series-Parallel Circuits |

The figures illustrate more complex examples of series-parallel connections. On the left, On the right, |