Series Circuits All Topics | PPT | web4study

# Series Circuits All Topics | PPT

Category: Electronics PPT , PPT ,

## Series Circuits

Topics Covered in this PPT

Why I Is the Same in All Parts of a Series Circuit

Total R Equals the Sum of All Series Resistances

Series IR Voltage Drops

Kirchhoff’s Voltage Law (KVL)

Polarity of IR Voltage Drops

Total Power in a Series Circuit

Series-Aiding and Series-Opposing Voltages

Analyzing Series Circuits with Random Unknowns

Ground Connections in Electrical and Electronic Systems

Troubleshooting: Opens and Shorts in Series Circuits

### Why IIs the Same in All Parts of a Series Circuit

Characteristics of a Series Circuit

• The current is the same everywhere in a series circuit.
• The total resistance is equal to the sum of the individual resistance values.
• The total voltage is equal to the sum of the IR voltage drops across the individual resistances.
• The total power is equal to the sum of the power dissipated by each resistance.
• Current is the movement of electric charge between two points, produced by the applied voltage.
• The free electrons moving away from one point are continuously replaced by free electrons flowing from an adjacent point in the series circuit.
• All electrons have the same speed as those leaving the voltage source.
• Therefore, I is the same in all parts of a series circuit.

Fig. 4-2: There is only one current in R1, R2, and R3 in series. (a) Electron drift is the same in all parts of a series circuit. (b) Current I is the same at all points in a series circuit.

• Series Current Formulas
• Total current is the same as the individual currents in the series string:
• IT = I1 = I2 = I3 = … = etc.
• Total current is equal to total voltage divided by total resistance:
• IT=VT/RT

• When a series circuit is connected to a voltage source, the free electrons must drift through all the series resistances.
• If there are two or more resistances in the same current path, the total resistance across the voltage source is the sum of all the resistances.

### Total R Equals the Sum of All Series Resistances

• Series Resistance Formulas
• The total resistance is the sum of the individual resistances.
• RT = R1 + R2 + R3 + R4 + R5
• Series Resistance Formulas
• Total resistance is equal to total voltage divided by the circuit current:
• Rt=Vt/It

### Series IR Voltage Drops

• By Ohm’s Law, the voltage across a resistance equals I × R.
• In a series circuit, the IR voltage across each resistance is called an IR drop or voltage drop, because it reduces the potential difference available for the remaining resistance in the circuit.

### Kirchhoff’s Voltage Law (KVL)

The IR drops must add to equal the applied voltage (KVL).

VT = V1 + V2 + V3 + V4 + V5

VT = IR1 + IR2 + IR3 + IR4 + IR5

VT = 0.1 × 10 + 0.1 × 15 + 0.1 × 20 + 0.1 × 30 + 0.1 × 25

VT = 1 V + 1.5 V + 2 V + 3 V + 2.5 V = 10 V

### Polarity of IR Voltage Drops

When current flows through a resistor, a voltage equal to IR is dropped across the resistor. The polarity of this IR voltage drop is:

• Negative at the end where the electrons enter the resistor.
• Positive at the end where the electrons leave the resistor.
• The rule is reversed when considering conventional current: positive charges move into the positive side of the IR voltage.
• The polarity of the IR drop is the same, regardless of whether we consider electron flow or conventional current.

### Total Power in a Series Circuit

• The power needed to produce current in each series resistor is used up in the form of heat.
• The total power used in the circuit is equal to the sum of the individual powers dissipated in each part of the circuit.
• Total power can also be calculated as VT × I

Finding Total Power

PT = P1 + P2 + P3 + P4 + P5

PT = I2R1 + I2R2 + I2R3 + I2R4 + I2R5

PT = 0.1 W + 0.15 W + 0.2 W + 0.3 W + 0.25 W  =  1 W

PT = 0.1 W + 0.15 W + 0.2 W + 0.3 W + 0.25 W  =  1 W

### Series-Aiding and Series-Opposing Voltages

• Series-aiding voltages are connected with polarities that allow current in the same direction:
• The positive terminal of one is connected to the negative terminal of the next.
• They can be added to the total voltage.
• Series-opposing voltages are the opposite: They are connected to produce opposing directions of current flow.
• The positive terminal of one is connected to the positive terminal of another.
• To obtain the total voltage, subtract the smaller voltage from the larger.
• Two equal series-opposing voltage sources have a net voltage of zero.

### Analyzing Series Circuits with Random Unknowns

• When trying to analyze a series circuit, keep the following principles in mind:

1.If I is known for one component, use this value in all components.

• The current is the same in all parts of a series circuit.

2.If I is unknown, it may be calculated in one of two ways:

• Divide VT by RT
• Divide an individual IR drop by its R.
• Remember not to mix a total value for an entire circuit with an individual value for part of the circuit.

3.If all individual voltage drops are known, add them to determine the applied VT.

• A known voltage drop may be subtracted from VT to find a remaining voltage drop.

### Ground Connections in Electrical and Electronic Systems

• In most electrical and electronic systems, one side of the voltage source is connected to ground.
• The reason for doing this is to reduce the possibility of electric shock.
• Figure 4-16 shows several schematic ground symbols:

• The ground is assumed to have a potential of 0 V regardless of the schematic symbol shown.
• These symbols are sometimes used inconsistently with their definitions. However, these symbols always represent a common return path for current in a given circuit.
• Voltages Measured with Respect to Ground
• When a circuit has a ground as a common return, measure the voltages with respect to this ground.

### Troubleshooting: Opens and Shorts in Series Circuits

The Effect of an Open in a Series Circuit

• An open circuit is a circuit with a break in the current path. When a series circuit is open, the current is zero in all parts of the circuit.
• The total resistance of an open circuit is infinite ohms.
• When a series circuit is open, the applied voltage appears across the open points.
• Applied voltage VT is still present, even with zero current.
• The voltage source still has its same potential difference across its positive and negative terminals.
• Example: The 120-V potential difference is always available from the terminals of a wall outlet.
• If an appliance is connected, current will flow.
• If you touch the metal terminals when nothing else is connected, you will receive a shock.

The Effect of a Short in a Series Circuit

• When part of a series circuit is shorted, the current flow increases.
• When part of a series circuit is shorted, the voltage drops across the non-shorted elements increase.
• The voltage drop across the shorted component drops to 0 V.
• When troubleshooting a series circuit containing three or more resistors, remember:
• The component whose voltage changes in the opposite direction of the other components is the defective component.