# Current

##### Intros
###### Lessons
1. A review on electric circuits so far.
2. What is current?
3. How are currents affected by series and parallel configurations?
4. What does "conventional current" mean?
5. What is the Junction Rule?
##### Examples
###### Lessons
1. Understanding Kirchhoff's Junction Rule by using the Water (River Current) Analogy
Find the volume of water passing through each point (A, C, and D).

1. Finding Current in Series Only Circuit vs. Parallel Only Circuit
1. Find the current through each resistor in series.

2. Find the current through the missing resistor (R2) in parallel.

2. Finding Current in Circuits with BOTH Series & Parallel Configurations
Find the electric current going through each resistor.

## Introduction to Electric Current

Welcome to our exploration of electric current, a fundamental concept in physics and electrical engineering! Before we dive into the details, I'd like to draw your attention to our introduction video. This video is a fantastic starting point, offering a visual and engaging overview of electric current. It's designed to make this sometimes-challenging topic more accessible and relatable. As we progress, you'll discover that electric current is essentially the flow of electric charge through a conductor, typically within an electric circuit. Understanding this concept is crucial for grasping how our modern world functions, from the simplest battery-operated toys to complex electronic devices. The video will help you visualize the movement of electrons, the role of voltage, and the basic components of an electric circuit. By the end of this section, you'll have a solid foundation to build upon as we delve deeper into the fascinating world of electricity.

## What is Electric Current?

Electric current is a fundamental concept in physics and electrical engineering that describes the flow of electric charge through a conductor. Imagine a river flowing steadily that's similar to how electric current works, but instead of water, we're dealing with tiny particles called electrons. These electrons, carrying negative electric field, move through a material in response to an electric field, creating what we call an electric current.

To understand electric current better, let's break down its basic principles. In a typical electric circuit, electrons flow from areas of high potential energy (negative terminal) to areas of low potential energy (positive terminal). This difference in energy levels is what we call voltage, and it's the driving force behind electric current. Just as water flows downhill due to gravity, electrons flow through a circuit due to this electrical "pressure" or voltage.

An analogy that might help visualize electric current is to think of a busy highway. The cars represent electrons, and the highway represents the conductor (like a wire). The speed limit signs could represent voltage the higher the voltage, the faster the electrons can move. The number of cars passing a certain point in a given time is similar to the amount of current flowing through a circuit.

In everyday life, we encounter electric current constantly, often without realizing it. When you turn on a light switch, you're completing a circuit and allowing current to flow through the light bulb, illuminating your room. Your smartphone's battery provides a steady current to power its various functions. Even the human body uses tiny electric currents to send signals through the nervous system!

Electric current is measured in amperes (A), named after the French physicist André-Marie Ampère. One ampere is defined as one coulomb of electric charge (about 6.24 x 10^18 electrons) moving past a point in a circuit per second. The flow of electrons in a circuit can be either direct current (DC), where electrons flow in one direction, or alternating current (AC), where the direction of flow changes periodically.

Understanding electric current is crucial for many applications. In homes and businesses, it powers our appliances, lights, and electronic devices. In industry, electric current drives motors, heats furnaces, and controls complex machinery. Even in nature, electric currents play a role from the dramatic lightning strikes during thunderstorms to the subtle bioelectric currents in living organisms.

To create an electric current, we need a complete circuit a closed loop that allows electrons to flow continuously. This circuit typically includes a power source (like a battery), conductors (usually wires), and one or more components that use the electrical energy (like a light bulb or motor). The flow of current can be controlled using switches, which open or close the circuit, and resistors, which limit the amount of current flowing through a particular part of the circuit.

Safety is paramount when dealing with electric current. While small currents are generally harmless, larger currents can be dangerous or even fatal if they pass through the human body. This is why electrical systems in homes and workplaces are designed with multiple safety features, including insulation, grounding, and circuit breakers.

As we continue to rely more heavily on electronic devices and renewable energy sources, understanding electric current becomes increasingly important. From the intricate circuits in our computers to the massive power grids that supply electricity to entire cities, electric current is the lifeblood of our modern, technology-driven world. By grasping its basic principles, we can better appreciate the complex systems that power our daily lives and inspire future innovations in electrical engineering and energy technology.

## Components of an Electric Circuit

Electric circuits are the foundation of modern electronics, powering everything from smartphones to household appliances. Understanding the main components of an electric circuit is crucial for anyone interested in electronics or electrical engineering. Let's explore the key elements that work together to create a complete circuit.

### Power Source

At the heart of every electric circuit is a power source. This component provides the electrical energy that drives the circuit. The most common power source in simple circuits is a battery. Batteries convert chemical energy into electrical energy, pushing electrons through the circuit. Other power sources include solar cells, which convert light into electricity, and wall outlets, which provide alternating current (AC) from the power grid.

### Conductors

Conductors are materials that allow electricity to flow freely through them. In most circuits, conductors take the form of wires, typically made of copper or aluminum. These wires connect the various components of the circuit, providing a path for the electric current to travel. It's important to note that conductors offer very little resistance to the flow of electricity, making them ideal for efficiently transferring energy throughout the circuit.

### Resistors

Resistors are components that oppose the flow of electric current. They play a crucial role in controlling the amount of current that flows through different parts of a circuit. Resistors come in various sizes and ratings, measured in ohms (Ω). By strategically placing resistors in a circuit, engineers can regulate voltage and current levels, protecting sensitive components and ensuring the circuit operates as intended.

### Switches

While not always present, switches are important components in many circuits. A switch acts as a controllable break in the circuit, allowing users to turn the flow of electricity on or off. When the switch is closed, it completes the circuit, allowing current to flow. When open, it breaks the circuit, stopping the flow of electricity.

The load in a circuit is the component that performs useful work with the electrical energy. This could be a light bulb that produces light, a motor that creates motion, or a speaker that generates sound. Loads convert electrical energy into other forms of energy, such as light, heat, or mechanical energy.

### How Components Work Together

To create a complete circuit, these components must be connected in a specific way. Let's consider a simple circuit with a battery, a switch, and a light bulb:

1. The battery serves as the power source, providing the electrical energy.
2. Conductive wires connect the positive terminal of the battery to one side of the switch.
3. Another wire connects the other side of the switch to one terminal of the light bulb (the load).
4. A final wire completes the circuit by connecting the other terminal of the light bulb back to the negative terminal of the battery.
5. When the switch is closed, it allows current to flow from the battery, through the wires and switch, to the light bulb, and back to the battery.
6. The resistor (which could be built into the light bulb or added separately) controls the amount of current flowing through the circuit, ensuring the bulb doesn't receive too much power and burn out.

This arrangement creates a closed loop, allowing electrons to flow continuously and power the light bulb. If any part of this loop is broken (for example, by opening the switch or disconnecting a wire), the circuit becomes incomplete, and the flow of electricity stops.

Understanding these basic components and how they interact is fundamental to grasping more complex electrical systems. As you delve deeper into the world of electronics, you'll encounter additional components like capacitors, transistors, and integrated circuits, each building upon these foundational elements to create increasingly sophisticated devices and systems.

By mastering the basics of electric circuits, you open the door to a fascinating world of innovation and technology. Whether you're a hobbyist looking to build your first circuit or a student beginning your journey in electrical engineering, this knowledge forms the essential groundwork for all your future explorations in the field of electronics.

## Series and Parallel Circuits

Hey there! Let's dive into the fascinating world of electrical circuits, specifically series and parallel circuits. These two types of circuits are fundamental to understanding how electricity flows and how our everyday devices work. Let's break it down in a way that's easy to grasp.

First, let's talk about series circuits. Imagine a string of holiday lights - that's a perfect example of a series circuit! In a series circuit, the current has only one path to follow. It flows through each component (like light bulbs or resistors) one after the other. Think of it as a single-file line where the electricity passes through each element before moving to the next.

Now, what happens in a series circuit? Well, the current is the same throughout the entire circuit. However, the voltage gets divided among the components. Each component causes a voltage drop, and these drops add up to the total voltage of the power source. It's like sharing a pizza - everyone gets a slice, but the more people there are, the smaller each slice becomes.

Series circuits have some advantages. They're simple to design and require less wiring. They're great for applications where you want devices to operate together, like those holiday lights we mentioned. If one goes out, they all do - which can be helpful for identifying problems.

But there are drawbacks too. If one component fails, the whole circuit stops working. Also, as you add more components, the overall resistance increases, which can reduce the current flow and make things like lights dimmer.

Now, let's switch gears and talk about parallel circuits. These are quite different! In a parallel circuit, the current has multiple paths to follow. It's like a highway with several lanes - the electricity can choose different routes to get to its destination.

In a parallel circuit, each component gets the full voltage of the power source. It's like everyone getting their own pizza instead of sharing slices! The current, however, is divided among the different paths. The total current in the circuit is the sum of the currents in each parallel branch.

Parallel circuits have some great advantages. If one component fails, the others keep working - this is why your house lights don't all go out when one bulb burns out. They also maintain a constant voltage across all components, which is crucial for many electronic devices.

The downside? Parallel circuits can be more complex to design and require more wiring. They can also draw more current from the power source, which might require beefier batteries or power supplies.

So, where do we see these circuits in real life? Series circuits are used in battery-powered devices where you need to increase voltage, like in a flashlight with multiple batteries. They're also used in some types of sensors and in old-fashioned Christmas lights.

Parallel circuits, on the other hand, are everywhere in our homes. Your household electrical system is a parallel circuit - that's why you can turn on the TV without affecting the refrigerator. They're also used in complex electronic devices, computer circuits, and even in solar panel arrays.

Understanding the difference between series and parallel circuits is key to grasping how electricity works in our world. Series circuits offer simplicity and are great for specific applications, while parallel circuits provide reliability and consistent power delivery to multiple components.

Remember, in a series circuit, current is constant but voltage drops across components. In a parallel circuit, voltage is constant across components, but current is divided. Both have their place in electrical engineering, and knowing when to use each is a valuable skill.

As you explore more about circuits, you'll find that many real-world applications use a combination of series and parallel configurations to achieve the desired results. It's all about finding the right balance for the specific needs of each device or system.

So next time you flip a light switch or charge your phone, take a moment to appreciate the clever circuit design that makes it all possible. Whether it's series, parallel, or a combination of both, these fundamental principles of electricity are working hard behind the scenes to power our modern world!

## Measuring Electric Current

Understanding how electric current is measured is crucial for anyone working with electrical systems or simply curious about the flow of electricity in everyday devices. At its core, electric current is the rate at which electric charge flows through a conductor, such as a wire. The standard unit for measuring electric current is the ampere, often shortened to "amp."

An ampere is defined as the flow of one coulomb of electric charge per second. To put this into perspective, imagine a steady stream of water flowing through a pipe. The ampere would be equivalent to the rate at which water passes through a specific point in the pipe. This analogy helps visualize the concept of current as a flow rather than a static quantity.

To measure electric current, electricians and technicians use specialized instruments called ammeters. An ammeter is designed to be connected in series with the circuit being measured, allowing the current to flow directly through the device. Modern ammeters are typically digital, providing quick and accurate readings of current flow.

For more versatile measurements, multimeters are commonly used. A multimeter is a multi-function device that can measure not only current but also voltage and resistance. When set to measure current, a multimeter functions as an ammeter. These devices are invaluable tools for both professionals and hobbyists working with electronics.

In household applications, current measurements are essential for understanding the power consumption of various appliances. For example, a typical refrigerator might draw about 1 to 2 amperes during normal operation, while a microwave oven could use 10 to 15 amperes when heating food. Understanding these current draws helps in proper circuit design and can even aid in energy conservation efforts.

To measure the current draw of a household appliance, one would typically use a clamp meter, which is a type of ammeter that can be clamped around a wire without needing to break the circuit. This non-invasive method is safe and convenient for measuring current in live circuits.

It's important to note that when measuring current, safety should always be the top priority. High currents can be dangerous, and improper use of measuring devices can lead to electrical shocks or damage to equipment. Always ensure that the measuring device is rated for the expected current and voltage levels of the circuit being tested.

For those new to electrical measurements, starting with battery-powered circuits or low-voltage DC systems is advisable. As an example, measuring the current draw of a small LED circuit can be a safe and educational exercise. Such a circuit might draw only a few milliamperes (thousandths of an ampere), providing a gentle introduction to current measurement techniques.

As you become more comfortable with current measurements, you can progress to more complex systems. Understanding how different appliances and devices consume electricity can lead to more efficient energy use and even help in troubleshooting electrical problems. Remember that in many household circuits, the current can vary depending on the device's operation mode or settings.

In conclusion, measuring electric current is a fundamental skill in electrical work, relying on the concept of amperes and utilizing tools like ammeters and multimeters. From simple battery-powered circuits to complex household appliances, understanding current flow provides valuable insights into electrical systems' operation and efficiency. As you explore this aspect of electricity, always prioritize safety and gradually build your experience with increasingly complex measurements.

## Ohm's Law and Current Calculations

Welcome to the fascinating world of electrical circuits! Today, we're going to explore Ohm's Law, a fundamental principle that helps us understand the relationship between voltage, current, and resistance in electrical systems. Don't worry if these terms sound intimidating; we'll break everything down step by step.

Ohm's Law, named after the German physicist Georg Ohm, states that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. In simpler terms, it means that as voltage increases, current increases, but as resistance increases, current decreases. This relationship is expressed by the equation: I = V / R, where I is current (measured in amperes), V is voltage (measured in volts), and R is resistance (measured in ohms).

Now, let's focus on how to calculate current using voltage and resistance. The process is straightforward once you understand the equation. Here's a step-by-step guide to help you master current calculations:

1. Identify the given values: Look for the voltage (V) and resistance (R) in the problem.
2. Write down Ohm's Law equation: I = V / R
3. Plug in the known values: Replace V and R with the given numbers.
4. Solve the equation: Divide voltage by resistance to find the current.

Let's walk through an example together. Imagine you have a circuit with a voltage source of 12 volts and a resistance of 4 ohms. To calculate the current:

1. Given: V = 12 volts, R = 4 ohms
2. Equation: I = V / R
3. Plug in values: I = 12 / 4
4. Solve: I = 3 amperes

See? It's not so difficult! The current flowing through this circuit is 3 amperes. Let's try another example to reinforce your understanding. This time, we have a circuit with a voltage of 9 volts and a resistance of 3 ohms. Can you guess the current before we calculate it?

1. Given: V = 9 volts, R = 3 ohms
2. Equation: I = V / R
3. Plug in values: I = 9 / 3
4. Solve: I = 3 amperes

Great job! The current is again 3 amperes. Notice how changing both voltage and resistance proportionally resulted in the same current. This illustrates the beauty of Ohm's Law and how it helps us predict electrical behavior.

As you practice more, you'll become more comfortable with these calculations. Remember, the key to mastering electrical equations is understanding the relationships between variables and applying them consistently. Don't be discouraged if it takes a few tries to get it right that's all part of the learning process!

• Always pay attention to units. Ensure you're using volts for voltage, ohms for resistance, and amperes for current.
• Double-check your math. Even small calculation errors can lead to incorrect results.
• Practice with various scenarios. Try problems with different voltage and resistance values to strengthen your skills.
• Visualize the circuit. Drawing a simple diagram can help you understand the problem better.

As you continue your journey in electrical engineering or physics, you'll find that Ohm's Law is just the beginning. It forms the foundation for understanding more complex electrical concepts and circuits. Keep practicing, stay curious, and don't hesitate to ask questions when you need clarification. With patience and persistence, you'll soon be calculating currents with ease and confidence!

## Safety and Electric Current

Electrical safety is paramount when dealing with electric current, as it can pose serious risks to human life and property. Understanding the dangers associated with high current and implementing proper safety measures are crucial for preventing electrical accidents. This article will explore the importance of electrical safety and provide essential tips for working with electrical devices.

High current poses significant hazards due to its potential to cause severe burns, muscle contractions, and even fatal cardiac arrest. The human body is particularly vulnerable to electrical current, with as little as 50 milliamps capable of causing serious harm. Recognizing these risks is the first step in ensuring electrical safety.

To prevent electrical accidents, it's essential to follow proper safety protocols. Always use insulated tools and wear appropriate personal protective equipment (PPE) when working with electrical systems. Rubber-soled shoes, insulated gloves, and safety glasses are crucial for protecting against electrical hazards. Additionally, ensure that all electrical equipment is properly grounded and regularly inspected for signs of wear or damage.

One of the most critical safety precautions is to always turn off the power source before performing any electrical work. Use a voltage tester to confirm that the circuit is de-energized before beginning any repairs or maintenance. Never assume that a circuit is dead simply because a switch is in the "off" position.

When working with electrical devices, it's important to be aware of your surroundings. Keep work areas dry and free from water or other conductive materials. Avoid using electrical equipment in wet conditions or near flammable substances. If you must work in damp environments, use ground fault circuit interrupters (GFCIs) to provide additional protection against electric shock.

Understanding and respecting the power of electricity is crucial for maintaining a safe work environment. Never overload electrical outlets or use damaged cords, as these can lead to overheating and potential fires. Be cautious of exposed wires and never attempt to repair frayed cords with tape replace them immediately.

In case of an electrical emergency, knowing how to respond quickly can save lives. Familiarize yourself with the location of circuit breakers and how to shut off power to the entire building if necessary. If someone becomes a victim of electric shock, do not touch them directly. Instead, use a non-conductive object to separate them from the electrical source before providing first aid or calling for emergency assistance.

Education and training play a vital role in electrical safety. Regularly update your knowledge of safety procedures and stay informed about new regulations and best practices in electrical work. Encourage a culture of safety in your workplace or home by sharing this information with others and leading by example.

Remember, electrical safety is not just for professionals it's important for everyone who uses electrical devices in their daily lives. By respecting the power of electricity and following proper safety guidelines, we can significantly reduce the risk of electrical accidents and create a safer environment for all.

## Conclusion

Electric current, the lifeblood of our modern world, is a fascinating concept that powers our daily lives. As we've explored in the introduction video, understanding electric current is crucial for grasping the fundamentals of electrical engineering. From the flow of electrons to the intricate dance of circuit components, this knowledge forms the foundation for countless technological advancements. Safety considerations are paramount when working with electricity, emphasizing the importance of proper education and precautions. The journey doesn't end here we encourage you to delve deeper into the world of electrical engineering. Explore advanced concepts, experiment with circuits, and unleash your creativity. The potential for innovation is limitless! Take the next step in your learning journey by engaging with more electrical engineering topics. Who knows? Your newfound knowledge might spark the next groundbreaking invention. Embrace the power of electric current and let it illuminate your path to a brighter, more electrifying future!

### A Review on Electric Circuits So Far

In this section, we will review the key concepts and components of electric circuits, focusing on the topic of current. This review will cover the definition of electric current, the differences between series and parallel circuits, and the tools and methods used to solve current problems in these circuits.

#### Step 1: Understanding Electric Current

Electric current is the flow of electric charge within a circuit. It is measured in amperes (A) and is a fundamental concept in understanding how electric circuits operate. In our previous lessons, we explored the nature of electric current and its behavior in different types of circuits. The main components that influence electric current are voltage (the potential difference) and resistance (the opposition to the flow of current).

#### Step 2: Series and Parallel Circuits

Electric circuits can be classified into two main types: series circuits and parallel circuits. In a series circuit, all components are connected end-to-end, forming a single path for the current to flow. This means that the same current flows through each component, but the voltage is divided among them. In contrast, a parallel circuit has multiple paths for the current to flow. Each component is connected across the same two points, so the voltage across each component is the same, but the current is divided among the different paths.

#### Step 3: Solving Current Problems in Series Circuits

To solve current problems in series circuits, we need to understand the relationship between voltage, current, and resistance, as described by Ohm's Law (V = IR). In a series circuit, the total resistance is the sum of the individual resistances. The current is the same throughout the circuit, so we can calculate the total current by dividing the total voltage by the total resistance. For example, if we have a series circuit with a total voltage of 12V and a total resistance of 6 ohms, the current would be 2A (12V / 6Ω = 2A).

#### Step 4: Solving Current Problems in Parallel Circuits

In parallel circuits, the total current is the sum of the currents through each parallel branch. The voltage across each branch is the same, but the current is divided based on the resistance of each branch. To find the total current, we can use the formula for the total resistance in parallel circuits: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn. Once we have the total resistance, we can use Ohm's Law to find the total current. For example, if we have a parallel circuit with a total voltage of 12V and two branches with resistances of 4 ohms and 6 ohms, the total resistance would be 2.4 ohms, and the total current would be 5A (12V / 2.4Ω = 5A).

#### Step 5: Tools and Methods for Calculating Current

To calculate current in electric circuits, we use several tools and methods. The most common tools are the ammeter, which measures current directly, and the voltmeter, which measures voltage. We also use mathematical methods such as Ohm's Law and Kirchhoff's Laws. Kirchhoff's Current Law (KCL) states that the total current entering a junction equals the total current leaving the junction. Kirchhoff's Voltage Law (KVL) states that the sum of the voltages around a closed loop equals zero. These laws help us analyze complex circuits and determine the current in each branch.

#### Step 6: Practical Applications and Examples

Understanding electric current and how to solve current problems is essential for designing and troubleshooting electric circuits. For example, in a household electrical system, knowing how to calculate the current can help prevent overloading circuits and ensure the safe operation of electrical devices. In electronic devices, precise current calculations are crucial for the proper functioning of components such as resistors, capacitors, and transistors.

#### Step 7: Summary and Key Takeaways

In summary, electric current is a fundamental concept in electric circuits, and understanding how to calculate and analyze current in series and parallel circuits is essential for anyone working with electrical systems. By using tools such as Ohm's Law and Kirchhoff's Laws, we can solve current problems and ensure the safe and efficient operation of electric circuits. Remember to always consider the total resistance, voltage, and current when analyzing circuits, and use the appropriate tools and methods to obtain accurate results.

### FAQs

1. #### What is electric current?

Electric current is the flow of electric charge through a conductor, typically measured in amperes (A). It occurs when electrons move from areas of high potential energy to areas of low potential energy in response to an electric field. This flow of charge is essential for powering electrical devices and systems.

2. #### How is electric current measured?

Electric current is measured using an ammeter or a multimeter set to measure current. These devices are connected in series with the circuit to directly measure the flow of charge. The standard unit of measurement is the ampere (A), which represents one coulomb of electric charge passing a point in a circuit per second.

3. #### What's the difference between AC and DC current?

Direct Current (DC) flows in one direction consistently, such as in batteries. Alternating Current (AC) periodically changes direction, typically used in household electricity. DC is common in low-voltage applications, while AC is efficient for long-distance power transmission and is used in most homes and businesses.

4. #### How does Ohm's Law relate to electric current?

Ohm's Law states that current (I) is equal to voltage (V) divided by resistance (R), expressed as I = V/R. This fundamental relationship helps calculate current when voltage and resistance are known, or determine other electrical properties of a circuit. It's essential for understanding and designing electrical systems.

5. #### What safety precautions should be taken when working with electric current?

Safety is crucial when working with electricity. Always turn off power sources before working on circuits, use insulated tools and wear appropriate protective equipment. Avoid working in wet conditions, never overload outlets, and regularly inspect electrical equipment for damage. Understanding the risks and following proper safety protocols can prevent accidents and injuries.

### Prerequisite Topics

Understanding the concept of current in physics is crucial, but it's equally important to grasp the foundational knowledge that supports it. One of the most significant prerequisite topics for comprehending current is the electric field. This fundamental concept plays a vital role in shaping our understanding of how electric charges interact and move, which is at the heart of current flow.

The electric field is a cornerstone of electromagnetism, providing the framework for understanding how electric charges exert forces on one another. When studying current, which is essentially the flow of electric charge, having a solid grasp of electric fields becomes indispensable. The electric field determines the direction and magnitude of the force acting on charged particles, which directly influences the movement of these charges in a conductor.

Consider a simple electric circuit. The flow of current in this circuit is driven by an electric field created by the voltage source. Without understanding how electric fields are generated and how they interact with charged particles, it would be challenging to fully comprehend why current flows in the direction it does or how its magnitude is determined.

Moreover, the concept of electric field strength is closely related to the potential difference, or voltage, across a conductor. This relationship is fundamental to Ohm's law, which is a cornerstone equation in the study of current. By understanding electric fields, students can more easily grasp how voltage drives current through a circuit and why materials with different resistivities respond differently to the same applied electric field.

The electric field also plays a crucial role in more advanced topics related to current, such as electromagnetic induction. When a conductor moves through a magnetic field, it experiences an induced electric field, which can generate a current. This principle is the basis for many practical applications, including electric generators and transformers.

Furthermore, in semiconductor physics, understanding electric fields is essential for grasping how charge carriers (electrons and holes) move within materials. This knowledge is fundamental to the operation of diodes, transistors, and other electronic components that rely on controlling current flow.

In conclusion, the electric field serves as a critical prerequisite topic for studying current. It provides the necessary foundation for understanding the forces that drive charge movement, the relationships between voltage and current, and the behavior of charged particles in various materials and devices. By mastering this concept, students will find themselves better equipped to tackle more complex aspects of current and electrical phenomena in their physics studies.

In this lesson, we will learn:

• A review on what is an electric circuit and the main components: battery (voltage), closed wire path (current), and devices/resistors that use up electricity (resistance).
• What is current?
• What is the difference between connecting your circuit in series vs. parallel configurations for resistors?
• What is electron flow/ electron current? How is it different from conventional current?
• Kirchhoffs 1st Rule: Junction Rule for solving current questions
• How to solve current problems for both series and parallel circuits by using the concepts of: (a) thinking of electric current as river water current and (b) Kirchhoffs 1st Rule (Junction Rule) for solving current problems

Notes:

• The electric current is the rate that electric charge is flowing through the circuit
• Electric current can be considered as a type of electricity
• Electricity is the energy from charged particles that can be either dynamic (moving) or static (not moving and accumulating in one place)
• The unit for current is the ampere (A), and can be measured with an ammeter connected in series
• In terms of current, the advantage of a parallel configuration is that the circuit will not fail as easily; even if one part of the circuit is faulty, the current can still flow through other pathways to make its way around a complete, closed circuit loop.
• In a series configuration, if one part is faulty, the whole circuit becomes faulty.
• In reality, the conventional current (rate of flow of positive charge from positive to negative battery terminal) is NOT what happens
• The real carrier of charge is the electron, which has negative charge.
• The rate of flow of negative charge is called electron flow or electron current, and it flows in the opposite direction to conventional current (from negative to positive battery terminal)
• Recall electrostatics: like charges repel, opposite charges attract. For conventional current, protons are being repelled away from the positive terminal and move toward the attracting negative terminal; for electron current, electrons are being repelled away from the negative terminal and move toward the attracting positive terminal
• Kirchhoffs 1st Rule, also known as the Junction Rule, states that the sum of currents entering a junction is equal to the sum of currents leaving that junction
• $I_{in} = I_{out}$
• The flow of electric charge within the circuit is conserved
• A junction is where the path of electric flow either splits or converges.
• We will use the water (river current) analogy for electric current
• The same volume of water will stay within the pipes (current within wires of circuit)
• The water can split and come back together (junction rule; the amount entering the split is the same as the amount leaving the split)