Name: capacitor energy and cdi ignition
Uploaded: 2023-09-18T17:11:16.000Z
Duration: 1 min 26 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

High School

Physics

Energy

PHYS.PS3.13

energy-stored-in-a-capacitor-problem-solving

Energy Stored in a Capacitor: Problem Solving

Capacitors act as temporary batteries storing electric potential energy that could be released over a short time.
In small engines, a capacitor-discharge ignition system is used that consists of a charging unit to charge a capacitor completely. Upon receiving a trigger, the capacitor rapidly discharges the stored energy to an ignition coil that, in turn, fires the spark plug to start the engine. 
The amount of energy stored by a capacitor-discharge ignition system depends on the value of the applied voltage and the capacitance of the capacitor.
Consider a fully charged capacitor with a charge of 375 micro coulomb and capacitance of 1.5 micro farad. Here the charge and capacitance are known quantities, and the voltage and energy are unknown quantities.
Using the known quantities, the voltage supplied to the system could be calculated to be 250 volt.
Upon substitution, the voltage and capacitance values give the value of the electric potential energy saved in the capacitor to be 0.047 joules.

energy stored in a capacitor: problem solving

In 1749, Benjamin Franklin coined the word battery for a series of capacitors connected to store energy. Capacitors store electric potential energy that can be released over a short time. This property means capacitors have a wide range of applications.
Capacitor-discharge ignition is a type of ignition system commonly found in small engines where the energy released from a capacitor ignites an induction coil that, in turn, fires the spark plug.
To calculate the energy stored in a capacitor of a typical CDI system, at least two of the following parameters should be known:
<ol>
	<li>The voltage applied across the capacitor</li>
	<li>The charge stored in the capacitor</li>
	<li>The capacitance of the capacitor</li>
</ol>
Since these three parameters are related by the equation given below, the unknown parameter can be calculated if any two parameters are known:
<img alt="Capacitance formula, V=Q/C, equation; electric potential, charge, capacitance relationship." src="/files/ftp_upload/13739/13739_Equation_1.svg" style="text-align: center; height: 40px;" data-altupdatedat="1761830439000" data-alt="Equation1" />
For any given case, the potential energy stored can be calculated using the values of capacitance, voltage, and charge:
<img alt="Capacitor energy equation UC=Q&#178;/2C=&#189;CV&#178;=&#189;QV, physics formula." src="/files/ftp_upload/13739/13739_Equation_2.svg" style="text-align: center; height: 40px;" data-altupdatedat="1761830439000" data-alt="Equation2" />

In 1749, Benjamin Franklin coined the word battery for a series of capacitors connected to store energy. Capacitors store electric potential energy that ...

Education

JoVE Core

Unit 1

Capacitance

KEY TERMS AND CONCEPTS

capacitor energy and cdi ignition

Capacitors store electric potential energy, and that energy can be released over a short time. This makes them useful in a range of applications. Benjamin Franklin coined the word battery in 1749 for a series of capacitors connected to store energy.

One common use is capacitor-discharge ignition, or CDI, in small engines. In a CDI system, the energy from a capacitor ignites an induction coil, which then fires the spark plug. To find the energy stored in a typical CDI capacitor, at least two of three values must be known: the applied voltage, the stored charge, and the capacitance.

These three values are linked by an equation, so the unknown quantity can be calculated when any two are given. The stored electric potential energy can also be found from capacitance, voltage, and charge. This makes capacitor energy problems a useful way to connect key circuit measurements with a real engine example.

Capacitor Energy and CDI Ignition

capacitors and capacitance

Parallel Plate Capacitors and Stored Charge

Parallel plate capacitors store electric charge between two conducting plates. The plates are separated by a distance, and the space between them is either a vacuum or an insulating material called a dielectric. Capacitors are used in many ways, from reducing static in radio reception to storing energy in heart defibrillators. When the two conductors are identical parallel plates, the device is called a parallel plate capacitor. If a battery is connected to an initially uncharged capacitor,...

spherical and cylindrical capacitor

Capacitance in Spheres and Cylinders

A spherical capacitor uses two concentric conducting spherical shells. The inner shell has radius R1, and the outer shell has radius R2. The shells carry equal and opposite charges, +Q and −Q. For an isolated conducting spherical capacitor, the outer shell can be treated as if it were at infinity. By symmetry, the electric field between the shells points radially outward. Using Gauss’s law on a spherical Gaussian surface of radius r gives the field magnitude between the shells. That electric...

capacitors in series and parallel

How Capacitor Networks Combine Charge

Capacitor networks combine charge and voltage in different ways, depending on how the capacitors are connected. When several capacitors act together, they can be treated as one equivalent capacitor. The total capacitance depends on the capacitance of each capacitor and on the connection type. In a series connection, the capacitors are connected one after another. The negative terminal of the first capacitor connects to the positive terminal of the second. When this series group is connected to...

equivalent capacitance

Finding Net Capacitance in Capacitor Networks

Capacitor networks can be arranged in series or parallel, and the connection type changes how charge and voltage are shared. When the network is connected to a battery, the potential drop across each capacitor and the charge stored in each one depend on that arrangement. The full network can then be replaced by one equivalent capacitor that stores the same charge for the same potential difference. To find the net capacitance, a capacitor network is grouped into series and parallel parts. A...

energy stored in a capacitor

Capacitor Charging and Stored Electric Energy

A charged capacitor stores electric potential energy by doing work during charging. This idea is similar to an archer pulling back a bowstring and storing elastic potential energy. When the arrow is released, that stored energy becomes motion. In the same way, the work put into a capacitor is stored as electric potential energy. For a parallel plate capacitor, the process starts when it is connected to a battery. The plate attached to the negative side of the battery gains extra electrons.

Capacitors store electric potential energy, and that energy can be released over a short time. This makes them useful in a range of applications. Benjamin Franklin coined the word battery in 1749 for a series of capacitors connected to store energy. One common use is capacitor-discharge ignition, or CDI, in small engines. In a CDI system, the energy from a capacitor ignites an induction coil, which then fires the spark plug. To find the energy stored in a typical CDI capacitor, at least two of...

capacitor with a dielectric

How Dielectrics Boost Capacitor Storage

A dielectric can help a parallel plate capacitor store more charge. In a basic capacitor, two conducting plates are separated by a set distance. Keeping the plates parallel can be mechanically difficult, especially when the plates are large and cannot touch each other. A dielectric is a non-conducting material with no free or loosely bound electrons. Placing this material between the plates creates a small gap and helps hold the plates together. It also increases the capacitor’s capacitance,...

dielectric polarization in a capacitor

How Dielectrics Change Capacitor Fields

Dielectrics change the electric field, voltage, and capacitance in a capacitor. A dielectric is an insulating material placed between the plates. Its presence affects how the field behaves inside the capacitor. Dielectrics are usually described as polar or nonpolar. In a polar dielectric, positive and negative charges are already separated, so each molecule has a permanent dipole moment. In a nonpolar dielectric, that charge separation is not present until an external electric field acts on...

gauss's law in dielectrics

Dielectric Effects on Electric Fields

Dielectric effects on electric fields explain how an insulating material changes the field between capacitor plates. When a polar dielectric is placed in an external field, its dipoles line up with the field. The opposite charges on nearby dipoles cancel each other, so the dielectric as a whole remains neutral. When the dielectric is inserted between the plates of a capacitor, bound charges appear near the edges of the dielectric and at the metal surface. These induced surface charges create...

potential due to a polarized object

Bound Charges in Polarized Dielectrics

Polarized dielectrics form when charges inside atoms or molecules shift slightly in an electric field. A neutral atom has a positive nucleus and a negative electron cloud. An external electric field pulls them in opposite directions. The pull is balanced by the attraction between the nucleus and electrons, so the atom becomes polarized. Some molecules, such as water, already have separated positive and negative sides. In a uniform electric field, the forces on those sides cancel. Even so, a...

susceptibility, permittivity and dielectric constant

susceptibility-permittivity-and-dielectric-constant

Dielectric Polarization and Capacitance

Dielectric polarization explains how a material responds to an external electric field. When a dielectric is placed in the field, its charges shift so the material becomes polarized. The charge density in the dielectric is the sum of bound and free charge densities, and the total charge density can also be written in terms of the total electric field. The bound charge density can be measured using polarization. This leads to a link between electric displacement and polarization. For linear...

electrostatic boundary conditions in dielectrics

electrostatic-boundary-conditions-in-dielectrics

Field Behavior at Dielectric Interfaces

Field behavior at dielectric interfaces changes when an electric field crosses from one homogeneous medium into another. That change creates a discontinuity, or sudden jump, in the field. The boundary conditions depend on which materials meet at the interface. When the two sides are different dielectric materials, the electric field and the electric displacement are linked through the material’s permittivity. Replacing the electric field with the electric displacement in the boundary...

key terms and concepts

Learn how capacitors store electric potential energy and how CDI ignition uses that energy to fire a spark plug. Solve for voltage, charge, or capacitance.

Capacitor Energy and CDI Ignition | JoVE K12

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Virginia  Standards of Learning

HIgh School

Physical Science

PS.9

PS.9.a

Electrical Current

Electrical current is defined as the rate at which charge flows. When there is a large current present, such as that used to run a refrigerator, a large ...

Drift Velocity

The high speed of electrical signals results from the fact that the force between charges acts rapidly at a distance. Thus, when a free charge is forced ...

Current Density

The total amount of current flowing through one unit value of a cross-sectional area is referred to as current density. If the current flow is uniform, ...

Resistivity

When a voltage is applied to a conductor, an electrical field is generated, and charges in the conductor feel the force due to the electrical field. The ...

Resistance

When a current moves through any conductor, the conductor causes some level of difficulty for the current to flow. The measure of that difficulty is known ...

Ohm's Law

Many materials exhibit a simple relationship between the values of current, voltage, and resistance, known as Ohm&#8217;s law. The current that flows ...

Non-ohmic Devices

In most substances, the current flow is proportional to the voltage applied to it. A simple relationship between the values of current, voltage, and ...

Investigate Ohm’s law (I=V/R) by conducting an experiment to determine the relationships between current and voltage, current and resistance, and voltage and resistance. Investigate Ohm’s law (I=V/R) by conducting an experiment to determine the relationships between current and voltage, current and resistance, and voltage and resistance. EXPLANATION:  Ohm’s law relates the current through a device or portion of a circuit to the voltage drop observed across that device. The voltage drop across a device will increase in a linear fashion as the current through that device is increased. The resistance of the device is given by the ratio of voltage drop to current across the device. In an ohmic device, this ratio will be constant. Simple, single-loop circuits may be analyzed by considering each resistor as part of the total (equivalent) resistance of the circuit. (It may be beneficial to describe non-ohmic devices, but such devices are beyond the scope of this standard.)

PHYS.PS3.11

Kirchhoff's Rules

Gustav Kirchhoff (1824&#8211;1887) devised two rules known as Kirchhoff&#39;s rules to analyze complex circuits, which cannot be analyzed with ...

Kirchoff's Rules: Application

Kirchhoff&#39;s rules quantify the current flowing through a circuit and the voltage variations around the loop in a circuit. Applying Kirchhoff&#39;s ...

Apply the law of conservation of energy and charge to assess the validity of Kirchhoff’s loop and junction rules when algebraically solving problems involving multiloop circuits.  Apply the law of conservation of energy and charge to assess the validity of Kirchhoff’s loop and junction rules when algebraically solving problems involving multiloop circuits.  EXPLANATION:  Analysis of circuits using Ohm’s Law is efficient for small, simple circuits. In more complex circuits, it is beneficial to evaluate the flow of charge and potential drops using Kirchhoff’s Rules. These rules present an excellent opportunity to consider conservation laws. The junction rule reflects a conservation of charge, while the loop rule addresses conservation of energy for a unit of charge. This may be presented by considering the capacity of each charge to either do work or produce heat. In a complete loop, all of that capacity will have been eliminated.

PHYS.PS3.12

Capacitors and Capacitance

A device consisting of two electrical conductors that are separated by a distance and used to store electrical charges is called a capacitor. The space ...

Spherical and Cylindrical Capacitor

A spherical capacitor consists of two concentric conducting spherical shells of radii R1&#160;(inner shell) and R2&#160;(outer shell). The shells ...

Capacitors in Series and Parallel

Multiple capacitors connected serve as electrical components in various applications. These multiple capacitors behave as a single equivalent capacitor, ...

Equivalent Capacitance

Multiple capacitors can be connected in a circuit in series or parallel configuration. When the capacitor combination is connected to a battery, the ...

Energy Stored in a Capacitor

When an archer pulls the string in a bow, he saves the work done in the form of elastic potential energy. When he releases the string, the potential ...

electric-field-of-parallel-conducting-plates

Electric Field of Parallel Conducting Plates

Gauss&#39; law relates the electric flux through a closed surface to the net charge enclosed by that surface. Gauss&#39;s law can be applied to find the ...

Predict the energy stored in a capacitor and how charge flows among capacitors connected in series or parallel. Predict the energy stored in a capacitor and how charge flows among capacitors connected in series or parallel. EXPLANATION:  Parallel plate capacitors provide a means to store an electric potential difference across the two plates. Charges can flow onto or off of the two plates when the poles are connected to a battery, until the potential difference across the plates is equal to the potential difference of the connected battery. When disconnected from the source, the potential difference remains in place across the capacitor. If the two ends are connected the two plates will return to their equipotential state. The flow of charge in capacitors should be explained by considering the point where charge ceases to flow due to the entire circuit having equal potential differences and justifying why current has stopped. A charged capacitor creates an electric field with the capacity to do work.

Conservation of Mechanical Energy

The mechanical energy E of a system is the sum of its potential energy U and the kinetic energy K of the objects within it. What happens to this ...

/files/media/science-education/science-education-thumbs/14702.jpg

Conservation of Energy

The terms &#39;conserved quantity&#39;&#160;and &#39;conservation law&#39;&#160;have specific scientific meanings in physics, which differ from the ...

Conservation of Energy: Application

When solving problems using the energy conservation law, the object (system) to be studied should first be identified. Often, in applications of energy ...

Recognize and communicate information about energy efficiency and/or inefficiency of machines used in everyday life. Recognize and communicate information about energy efficiency and/or inefficiency of machines used in everyday life.   EXPLANATION:  An understanding of conservation of energy should lead to conversations about the efficiency of a device. A well designed device should utilize as much of the available energy as possible for the desired task. Other energy will be converted to forms, such as heat and noise, which may not be immediately useful based on the intended use for the device.

PHYS.PS3.14

Electromagnetic Waves

James Clerk Maxwell formulated a single theory combining all the electric and magnetic effects scientists knew during that time, calling the phenomena his ...

Compare and contrast the process, design, and performance of numerous nextgeneration energy sources (hydropower, wind power, solar power, geothermal power, biomass power etc.). Compare and contrast the process, design, and performance of numerous nextgeneration energy sources (hydropower, wind power, solar power, geothermal power, biomass power etc.).  EXPLANATION: The physics phenomena explored throughout this course are utilized engineers in designing energy capturing systems that are not reliant on non-renewable resources. Students can research these processes and relate them to both the scientific principles underlying the various processes, as well as implications of system design and efficiency behind improvements to these processes over time.

PHYS.PS3.15

Capacitor Energy and CDI Ignition

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