Electrical Engineering: Basic Laws (13 of 31) Series Resistors and Voltage Division

Summary

The video explains the concept of a voltage divider in a series circuit. Using a 20-volt source and two resistors (4 ohms and 6 ohms), it demonstrates how to split the voltage into 8 volts and 12 volts across each resistor. The process involves calculating total resistance, current, and voltage drops using Ohm's law. The voltage divider can be used to reduce a voltage source for specific needs, such as powering a load resistor with the appropriate voltage. An alternative formula for voltage dividers is also introduced for more flexibility in designing circuits.

Takeaways

• 🔋 The circuit being discussed is a series circuit and a voltage divider using a 20-volt source.
• 🔧 The negative end of the voltage source is connected to ground, setting the voltage to 0V at that point.
• 🧮 The goal is to find the voltage drops across two resistors, labeled as V1 (across R1) and V2 (across R2).
• 🔌 A voltage divider allows the reduction of the overall voltage into smaller portions, suitable for other loads in a circuit.
• 📏 The total resistance in the circuit is the sum of the resistors R1 and R2, giving a total resistance of 10 ohms.
• ⚡ Using Ohm's Law, the current in the circuit is calculated as 2 amps, determined by dividing the voltage by the total resistance.
• 📐 The voltage drop across R1 (V1) is calculated as 8 volts, and the drop across R2 (V2) is 12 volts.
• 🔄 The circuit divides the 20V source into 8V and 12V across the resistors, matching the expected total voltage drop.
• 📉 Voltage dividers can be used to provide the correct lower voltage for different components or loads in a circuit.
• 📝 Another way to calculate the voltage across a resistor in a voltage divider is by using the ratio of the resistances, as shown in the final example using V2 = 20V * (6/10).

Q & A

What is a voltage divider?

A voltage divider is a circuit configuration that divides the input voltage into smaller output voltages using a series of resistors.

How is the total resistance in a series circuit calculated?

In a series circuit, the total resistance is the sum of the individual resistances. For this circuit, the total resistance is R1 + R2, which equals 4 ohms + 6 ohms = 10 ohms.

How do you calculate the current in a series circuit?

The current is calculated using Ohm's law: I = V / R, where V is the total voltage and R is the total resistance. In this case, I = 20V / 10 ohms = 2 amps.

How can you find the voltage drop across each resistor in the series circuit?

The voltage drop across each resistor is calculated using the formula V = I * R. For R1, the voltage drop is V1 = 2 amps * 4 ohms = 8 volts. For R2, the voltage drop is V2 = 2 amps * 6 ohms = 12 volts.

Why is this circuit called a voltage divider?

This circuit is called a voltage divider because it takes an input voltage (20V in this case) and divides it across two resistors, resulting in smaller voltages (8V and 12V).

What is the purpose of using a voltage divider in a circuit?

The purpose of a voltage divider is to reduce a higher input voltage to a lower output voltage, which can then be used to drive a load or another part of a circuit that requires a lower voltage.

What happens to the remaining 8 volts in the circuit after the voltage divider reduces the voltage to 12 volts?

The remaining 8 volts is not used in this particular case because the objective was to reduce the 20 volts down to 12 volts. The extra voltage does not need to be connected to anything.

How can you determine the voltage across a specific resistor using the ratio of resistances?

You can determine the voltage across a resistor in a voltage divider by using the formula V2 = V * (R2 / (R1 + R2)). In this case, V2 = 20V * (6 ohms / (4 ohms + 6 ohms)) = 12 volts.

What role does grounding play in this circuit?

Grounding ensures that the negative end of the voltage source is set to 0 volts, providing a reference point for the circuit and ensuring that the voltage drops can be calculated accurately.

Why is Ohm's law important in analyzing this circuit?

Ohm's law is important because it allows you to calculate both the current through the circuit and the voltage drops across the resistors, which are key to understanding how the voltage divider works.