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Cards (42)

Section 1

(42 cards)

References Capacitors

Front

https://en.wikipedia.org/wiki/Capacitor http://www.facstaff.bucknell.edu/mastascu/elessonshtml/lc/capac1.htm https://en.wikipedia.org/wiki/Capacitance http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capac.html https://en.wikipedia.org/wiki/Electric_charge http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecur.html https://en.wikipedia.org/wiki/Voltage http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html http://www.allaboutcircuits.com/textbook/direct-current/chpt-13/factors-affecting-capacitance/ http://physicsmax.com/factors-affecting-capacitance-parallel-plate-capacitor-7596 http://electronics.stackexchange.com/questions/3062/what-are-some-reasons-to-connect-capacitors-in-series http://www.allaboutcircuits.com/textbook/direct-current/chpt-13/series-and-parallel-capacitors/

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Electrostatics Coulomb's Law

Front

The interaction between charged objects is a non-contact force that acts over some distance of separation. Charge, charge and distance. Every electrical interaction involves a force that highlights the importance of these three variables. Whether it is a plastic golf tube attracting paper bits, two like-charged balloons repelling or a charged Styrofoam plate interacting with electrons in a piece of aluminum, there is always two charges and a distance between them as the three critical variables that influence the strength of the interaction. In this section of Lesson 3, we will explore the importance of these three variables.

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The force per unit charges is knows as ______________.

Front

electric flux

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Batteries Series and Parallels Battery Bank

Front

What is a bank of batteries? No, it's not some kind of financial battery establishment. A battery bank is the result of joining two or more batteries together for a single application. What does this accomplish? Well, by connecting batteries, you can increase the voltage or amperage, or both. When you need more power, instead of getting yourself a massive super tanker of a battery, you can construct a battery bank. The first thing you need to know is that there are 2 ways to successfully connect two or more batteries. The first is Series and the second is Parallel. Lets start with Series Series adds the voltage of the two batteries, but keeps the same amperage rating (also known as Amp Hours). For example, these two 6 Volt batteries joined in series now produce 12 Volts, but still have a total capacity of 10 Amps.Jumper Cables To connect batteries in a series, use a jumper wire to connect the negative terminal of the first battery to the positive terminal of the second battery. Use another set of cables to connect the open positive and negative terminals to your application. Never cross the remaining open positive and open negative terminals with each other, as this will short circuit the batteries and cause damage or injury. It is best to be sure the batteries you're connecting have the same voltage and capacity rating. Otherwise, you may end up with charging problems, and shortened battery life. The other type of connection is Parallel. Parallel connections will increase your current rating, but the voltage will stay the same. In the diagram to the left, we're back to 6 Volts, but the Amps increase to 20. It's important to note that because the amperage of the batteries increased, you may need a heavier duty cable to avoid the cables burning out. Alligator ClipsTo join batteries in parallel, use a set of cables to connect both the positive terminals and another set of cables to connect both the negative terminals of both batteries to each other. Negative to negative and positive to positive. You then connect your load to ONE of the batteries, but both drain equally. It is also possible to connect batteries in what is called a Series/Parallel configuration This may sound confusing, but we will explain below. This is the way you can increase your voltage output and current rating. To do this successfully, you need at least 4 batteries. f you have two sets of batteries already connected in parallel, you can join them together to form a series. In the diagram on the left, we have a bank that produces 12 Volts and has 20 Amp Hours. Don't get lost now. Remember, electricity flows through a parallel connection just the same as it does in a single battery. It can't tell the difference. Therefore, you can connect two parallel connections in a series as you would two batteries. Only one cable is needed, a bridge between a positive terminal from one parallel bank to a negative terminal from the other parallel bank. It's alright if a terminal has more than one cable connected to it. It is necessary to successfully construct these kinds of battery banks. In theory, you can connect as many batteries together as you want. But when you start to construct a tangled mess of batteries and cables, it can be very confusing, and confusion can be dangerous. Keep in mind the requirements for your application, and stick to them. Also, use batteries of the same capabilities. Avoid mixing and matching battery sizes wherever possible

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Electrostatics Uniform Electric Field

Front

Set up when there are two straight parallel electrodes (plates) that have a potential difference between them. If a positive charge is placed at a point halfway between the plates then it will move toward the negative electrode (electric attraction) along the electric field lines. The uniform electric field is an approximation that makes for simple calculations that don't require differential calculus. Every field will have at least some irregularity, although some can be very nearly uniform. The equation for magnitude of a uniform electric field is: E=−Δϕdwhere E is the field, Δ is the potential difference between the plates, and d is the distance between the plates. For the case of a positive charge q to be moved from a point A with a certain potential (V1) to a point B with another potential (V2), that equation is: W=−q(V2−V1)The difference (V2-V1) can also be represented as ∆V or VAB. In uniform fields it is also simple to calculate potential difference: VAB=EdIn this case, field strength is E, and distance between points A and B is d.

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Capacitors Basic relationship of Capacitance, Charge, and Voltage Definition of Voltage

Front

Voltage is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against a static electric field to move the test charge between two points and is measured in units of volts (a joule per coulomb). Voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three.[1][2] A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy (electromotive force), or lost, used, or stored energy (potential drop).

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Introducing a non-conducting medium between two charges, the force between them _______?

Front

decreases

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Batteries Voltage and Power Capacity

Front

Power capacity is how much energy is stored in the battery. This power is often expressed in Watt-hours (the symbol Wh). A Watt-hour is the voltage (V) that the battery provides multiplied by how much current (Amps) the battery can provide for some amount of time (generally in hours). Voltage Amps hours = Wh. Since voltage is pretty much fixed for a battery type due to its internal chemistry (alkaline, lithium, lead acid, etc), often only the Amps*hour measurement is printed on the side, expressed in Ah or mAh (1000mAh = 1Ah). To get Wh, multiply the Ah by the nominal voltage. For example, lets say we have a 3V nominal battery with 1Amp-hour capacity, therefore it has 3 Wh of capacity. 1 Ah means that in theory we can draw 1 Amp of current for one hour, or 0.1A for 10 hours, or 0.01A (also known as 10 mA) for 100 hours. The way the power capability is measured is in C's. A C is the Amp-hour capacity divided by 1 hour. So the C of a 2Ah battery is 2A. The amount of current a battery 'likes' to have drawn from it is measured in C. The higher the C the more current you can draw from the battery without exhausting it prematurely. Lead acid batteries can have very high C values (10C or higher) , and lithium coin cells have very low ones (0.01C)

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Batteries Series and Parallels Single-Cell Configuation

Front

The single-cell configuration is the simplest battery pack; the cell does not need matching and the protection circuit on a small Li-ion cell can be kept simple. Typical examples are mobile phones and tablets with one 3.60V Li-ion cell. Other uses of a single cell are wall clocks, which typically use a 1.5V alkaline cell, wristwatches and memory backup, most of which are very low power applications. The nominal cell voltage for a nickel-based battery is 1.2V, alkaline is 1.5V; silver-oxide is 1.6V and lead acid is 2.0V. Primary lithium batteries range between 3.0V and 3.9V. Li-ion is 3.6V; Li-phosphate is 3.2V and Li-titanate is 2.4V. Li-manganese and other lithium-based systems often use cell voltages of 3.7V and higher. This has less to do with chemistry than promoting a higher watt-hour (Wh), which is made possible with a higher voltage. The argument goes that a low internal cell resistance keeps the voltage high under load. For operational purposes these cells go as 3.6V candidates.

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Electrostatics Electric Charge

Front

symbol: q for point charges, Q for charged plates, Unit: Coulombs All objects are charged in some multiple of the fundamental charge (1.6x10^-19 C) because charge is quantized based on either protons or electrons. Charge is also conserved in all interactions.

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When three capacitators are joined in series, the total capacitance is ___________.

Front

less than the value of the minimum capacitance

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Electrostatics Electric Field

Front

Symbol: E, Units: N/C or V/m The effect of a charged object on an area of space. E is defined as the force per Coulomb of charge that would be applied to a test charge IF it is placed at a particular location. It exists whether or not a charge is actually there. E field always goes from + to - and is perpendicular to both isolines of equipotential and surfaces of charged objects. E is constant within parallel plates except at the edges. E = F/q = kq/r^2 for point charges E = ΔV/r for parallel plates

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The unit of capacitance is _______.

Front

Joule - Coulomb called Weber

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Capacitors Physical factors that determine capacitance

Front

There are three basic factors of capacitor construction determining the amount of capacitance created. These factors all dictate capacitance by affecting how much electric field flux (relative difference of electrons between plates) will develop for a given amount of electric field force (voltage between the two plates): PLATE AREA: All other factors being equal, greater plate area gives greater capacitance; less plate area gives less capacitance. Explanation: Larger plate area results in more field flux (charge collected on the plates) for a given field force (voltage across the plates). PLATE SPACING: All other factors being equal, further plate spacing gives less capacitance; closer plate spacing gives greater capacitance. Explanation: Closer spacing results in a greater field force (voltage across the capacitor divided by the distance between the plates), which results in a greater field flux (charge collected on the plates) for any given voltage applied across the plates DIELECTRIC MATERIAL: All other factors being equal, greater permittivity of the dielectric gives greater capacitance; less permittivity of the dielectric gives less capacitance. Explanation: Although its complicated to explain, some materials offer less opposition to field flux for a given amount of field force. Materials with a greater permittivity allow for more field flux (offer less opposition), and thus a greater collected charge, for any given amount of field force (applied voltage).

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Batteries Series and Parallels Series/Parallel Connection

Front

The series/parallel configuration shown in Figure 6 enables design flexibility and achieves the desired voltage and current ratings with a standard cell size. The total power is the product of voltage-times-current; four 1.20V cells multiplied with 1000mAh produce 4.8Wh. Four 18650 Energy Cells with 3,000mAh each can be connected in series and parallel as shown to get 7.2V and 12Wh. The slim cell allows flexible pack design but a protection circuit is needed. Li-ion lends well to serial/parallel configurations but the cells need monitoring to stay within voltage and current limits. Integrated circuits (ICs) for various cell combinations are available to supervise up to 13 Li-ion cells. Larger packs need custom circuits, and this also applies to the Tesla Model 85 that devours over 7000 18650 cells to make up the 90kWh pack.

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Electrostatics The Principle of Superposition

Front

The net electric force on a charge (q) due to a collection of other charges (Q's) is equal to the sum of the individual forces that each of the Q's alone exerts on q.

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Capacitors Reasons for connecting capacitors in series or in parallel

Front

Usually you either combine capacitors in parallel because you want to increase the total capacitance while fitting the components in a certain shape/position, or you just combine capacitors by buying a single capacitor of a larger value. Combining capacitors in series reduces the total capacitance, and isn't very common, but what are some possible uses for it? It shouldn't be used to increase the voltage rating, for instance, since you can't guarantee that the middle will be at half the DC voltage of the total, without using bleeder resistors.

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Capacitors

Front

A passive two-terminal electrical component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While capacitance exists between any two electrical conductors of a circuit in sufficiently close proximity, a capacitor is specifically designed to provide and enhance this effect for a variety of practical applications by consideration of size, shape, and positioning of closely spaced conductors, and the intervening dielectric material. A capacitor was therefore historically first known as an electric condenser.

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Capacitors Basic relationship of Capacitance, Charge, and Voltage Definition of Capacitance

Front

Capacitance is the ability of a body to store an electric charge. There are two closely related notions of capacitance: self capacitance and mutual capacitance, that are usually both designated by the same term capacitance. A material with a large self capacitance holds more electric charge at a given voltage, than one with low capacitance. Any object that can be electrically charged exhibits self capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three fundamental electronic components (along with resistors and inductors). The capacitance is a function only of the geometry of the design (e.g. area of the plates and the distance between them) and the permittivity of the dielectric material between the plates of the capacitor. For many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them. The SI unit of capacitance is the farad (symbol: F), named after the English physicist Michael Faraday. A 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates.

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References Batteries

Front

https://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations http://www.zbattery.com/Connecting-Batteries-in-Series-or-Parallel http://www.enerdrive.com.au/connecting-batteries-in-series-or-parallel/

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Electrostatics Coulomb's Law: Force as a Vector Quantity

Front

The electrical force, like all forces, is typically expressed using the unit Newton. Being a force, the strength of the electrical interaction is a vector quantity that has both magnitude and direction. The direction of the electrical force is dependent upon whether the charged objects are charged with like charge or opposite charge and upon their spatial orientation. By knowing the type of charge on the two objects, the direction of the force on either one of them can be determined with a little reasoning. In the diagram below, objects A and B have like charge causing them to repel each other. Thus, the force on object A is directed leftward (away from B) and the force on object B is directed rightward (away from A). On the other hand, objects C and D have opposite charge causing them to attract each other. Thus, the force on object C is directed rightward (toward object D) and the force on object D is directed leftward (toward object C). When it comes to the electrical force vector, perhaps the best way to determine the direction of it is to apply the fundamental rules of charge interaction (opposites attract and likes repel) using a little reasoning. Electrical force also has a magnitude or strength. Like most types of forces, there are a variety of factors that influence the magnitude of the electrical force. Two like-charged balloons will repel each other and the strength of their repulsive force can be altered by changing three variables. First, the quantity of charge on one of the balloons will affect the strength of the repulsive force. The more charged a balloon is, the greater the repulsive force. Second, the quantity of charge on the second balloon will affect the strength of the repulsive force. Gently rub two balloons with animal fur and they repel a little. Rub the two balloons vigorously to impart more charge to both of them, and they repel a lot. Finally, the distance between the two balloons will have a significant and noticeable effect upon the repulsive force. The electrical force is strongest when the balloons are closest together. Decreasing the separation distance increases the force. The magnitude of the force and the distance between the two balloons is said to be inversely related.

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Electrostatics Electric Potential

Front

k = Q/r Q= point source charge r = distance from Q Positive charges want to move to regions of lower potential Negative charges want to move to regions of higher potential Symbol: V, Units: volts Electrical potential energy per Coulomb of charge (based on location in an electric field) When conductors touch, the distribute charge until potential is equal.

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Total potential difference across the combination of three battery cells becomes maximum when?

Front

all three cells are connected in parallel Two cells are connected in parallel and third cells in series with combination

Back

The presence of a dielectric between the plates of a capacitor results in _____________?

Front

the sum of capacitance any two capacitors

Back

The unit of electric intensity is ____.

Front

N C/m

Back

Battery cells are connected in parallel to _________.

Front

increase the current capacity

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Electrostatics Potential Difference

Front

Symbol: ΔV, Units voltage, Difference in electrical potential between two locations. ΔV = zero within a conductor ΔU = qΔV for all situations E = ΔV/r and U = 1/2QΔV for parallel plates

Back

One joule per coulomb is called

Front

one Sauss

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Electrostatics Coulomb's Law: Equation

Front

Back

Batteries Series and Parallels Series Connection

Front

Portable equipment needing higher voltages use battery packs with two or more cells connected in series. Figure 2 shows a battery pack with four 1.2V nickel-based cells in series, also known as 4S, to produce 4.8V. In comparison, a six-cell lead acid string with 2V/cell will generate 12V, and four Li-ion with 3.6V/cell will give 14.4V. If you need an odd voltage of, say, 9.50 volts, connect five lead acid, eight NiMH or NiCd, or three Li-ion in series. The end battery voltage does not need to be exact as long as it is higher than what the device specifies. A 12V supply might work in lieu of 9.50V; most battery-operated devices can tolerate some over-voltage but quit on low voltage, but don't go too high. High voltage batteries keep the conductor size small. Cordless power tools run on 12V and 18V batteries; high-end models use 24V and 36V. Most e-bikes come with 36V Li-ion, some are 48V. The car industry wanted to increase the starter battery from 12V (14V) to 36V, better known as 42V, by placing 18 lead acid cells in series. Logistics of changing the electrical components and arcing problems on mechanical switches derailed the move. Some mild hybrid cars run on 48V Li-ion and use DC-DC conversion to 12V for the electrical system. Starting the engine is often done by a separate 12V lead acid battery. Early hybrid cars ran on a 148V battery; electric vehicles have packs with 450-500V. Such a battery needs more than 100 Li-ion cells connected in series. High-voltage batteries require careful cell matching, especially when drawing heavy loads or when operating at cold temperatures. With multiple cells connected in a string, the possibility of one cell failing is real and this would cause a failure. To prevent this from happening, a solid state switch in some large packs bypasses the failing cell to allow continued current flow, albeit at a lower sting voltage. Cell matching is a challenge when replacing a faulty cell in an aging pack. A new cell has a higher capacity than the others, causing an imbalance. Welded construction adds to the complexity of the repair, and this is why battery packs are replaced as a unit. High-voltage batteries in electric vehicles, in which a full replacement would be prohibitive, divide the pack into modules, each consisting of a specific number of cells. If one cell fails, only the affected module is replaced. A slight imbalance might occur if the new module is fitted with new cells. (See BU-910: How to Repair a Battery Pack.) Figure 3 illustrates a battery pack in which "cell 3" produces only 0.6V instead of the full 1.20V. With depressed operating voltage, this battery reaches the end-of-discharge point sooner than a normal pack. The voltage collapses and the device turns off with a "Low Battery" message. Batteries in drones and remote controls for hobbyist requiring high load current often exhibit an unexpected voltage drop if one cell in a string is weak. Drawing maximum current stresses frail cells, leading to a possible crash. Reading the voltage after a charge does not identify this anomaly; examining the cell-balance or checking the capacity with a battery analyzer will.

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Electrostatics

Front

The study of stationary electric charges or fields as opposed to electric currents.

Back

The change in potential energy of a unit charge between two points in an electrical field is called

Front

potential difference

Back

Batteries Series and Parallels Parallel Connection

Front

If higher currents are needed and larger cells are not available or do not fit the design constraint, one or more cells can be connected in parallel. Most battery chemistries allow parallel configurations with little side effect. Figure 4 illustrates four cells connected in parallel in a P4 arrangement. The voltage of the illustrated pack remains at 1.20V, but the current handling and runtime are increased fourfold. A cell that develops a high resistance or opens is less critical in a parallel circuit than in series configuration, but a failing cell will reduce the total load capability. It's like an engine only firing on three cylinders instead of on all four. An electrical short, on the other hand, is more serious as the faulty cell drains energy from the other cells, causing a fire hazard. Most so-called electrical shorts are mild and manifest themselves as elevated self-discharge. A total short can occur through reverse polarization or dendrite growth. Large packs often include a fuse that disconnects the failing cell from the parallel circuit if it were to short. Figure 5 illustrates a parallel configuration with one faulty cell.

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References Electrostatics

Front

https://en.wikipedia.org/wiki/Electrostatics https://www.khanacademy.org/science/electrical-engineering/ee-electrostatics https://www.khanacademy.org/science/physics/electric-charge-electric-force-and-voltage http://www.physicsclassroom.com/class/estatics/Lesson-3/Coulomb-s-Law http://www.physics4kids.com/files/elec_coulomb.html https://www.boundless.com/physics/textbooks/boundless-physics-textbook/electric-potential-and-electric-field-18/overview-139/uniform-electric-field-501-6060/ http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/Web/Forces_and_fields_creative_commons/7304/7304_06.htm https://www.reference.com/science/uniform-electric-field-102d62b606b3eabb

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Capacitors Basic relationship of Capacitance, Charge, and Voltage Definition of Charge

Front

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charges: positive and negative. Like charges repel and unlike attract. An object is negatively charged if it has an excess of electrons, and is otherwise positively charged or uncharged. The SI derived unit of electric charge is the coulomb (C). In electrical engineering, it is also common to use the ampere-hour (Ah), and, in chemistry, it is common to use the elementary charge (e) as a unit. The symbol Q often denotes charge. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that don't require consideration of quantum effects.

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Electrostatics Uniform Electric Field (continued)

Front

A uniform field is that in which the electric field is constant throughout. Just like the so-called "frictionless surface" in mechanics, the uniform field is an ideal but unreal situation that makes for simpler calculations. Equations involving non-uniform electric fields require use of differential calculus. Uniformity in an electric field can be approximated by placing two conducting plates parallel to one another and creating a potential difference between them. In such a case there will be slight variations in the field near its edges, but it will be approximately constant throughout every other area. The equation for magnitude of a uniform electric field is: E=−Δϕd where E is the field, Δ is the potential difference between the plates, and d is the distance between the plates. The coefficient of -1 arises from the fact that positive charges repel, and thus a positive charge will be pushed away from the positive plate and in a direction opposite that of the increasing voltage. Uniformity of an electric field allows for simple calculation of work performed when a test charge is moved across it. For the case of a positive charge q to be moved from a point A with a certain potential (V1) to a point B with another potential (V2), that equation is: W=−q(V2−V1) The difference (V2-V1) can also be represented as ∆V or VAB. In uniform fields it is also simple to relate ∆V to field strength and distance (d) between points A and B: VAB=Ed

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Electrostatics Coulomb's Law: Equation (continued)

Front

The quantitative expression for the effect of these three variables on electric force is known as Coulomb's law. Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. Where Q1 represents the quantity of charge on object 1 (in Coulombs), Q2 represents the quantity of charge on object 2 (in Coulombs), and d represents the distance of separation between the two objects (in meters). The symbol k is a proportionality constant known as the Coulomb's law constant. The value of this constant is dependent upon the medium that the charged objects are immersed in. In the case of air, the value is approximately 9.0 x 109 N • m2 / C2. If the charged objects are present in water, the value of k can be reduced by as much as a factor of 80. It is worthwhile to point out that the units on k are such that when substituted into the equation the units on charge (Coulombs) and the units on distance (meters) will be canceled, leaving a Newton as the unit of force. The Coulomb's law equation provides an accurate description of the force between two objects whenever the objects act as point charges. A charged conducting sphere interacts with other charged objects as though all of its charge were located at its center. While the charge is uniformly spread across the surface of the sphere, the center of charge can be considered to be the center of the sphere. The sphere acts as a point charge with its excess charge located at its center. Since Coulomb's law applies to point charges, the distance d in the equation is the distance between the centers of charge for both objects (not the distance between their nearest surfaces). The symbols Q1 and Q2 in the Coulomb's law equation represent the quantities of charge on the two interacting objects. Since an object can be charged positively or negatively, these quantities are often expressed as "+" or "-" values. The sign on the charge is simply representative of whether the object has an excess of electrons (a negatively charged object) or a shortage of electrons (a positively charged object). It might be tempting to utilize the "+" and "-" signs in the calculations of force. While the practice is not recommended, there is certainly no harm in doing so. When using the "+" and "-" signs in the calculation of force, the result will be that a "-" value for force is a sign of an attractive force and a "+" value for force signifies a repulsive force. Mathematically, the force value would be found to be positive when Q1 and Q2 are of like charge - either both "+" or both "-". And the force value would be found to be negative when Q1 and Q2 are of opposite charge - one is "+" and the other is "-". This is consistent with the concept that oppositely charged objects have an attractive interaction and like charged objects have a repulsive interaction. In the end, if you're thinking conceptually (and not merely mathematically), you would be very able to determine the nature of the force - attractive or repulsive - without the use of "+" and "-" signs in the equation.

Back

A charge Q exerts a 12 N force on another charge q. If the distance between the charges is doubled, what is the magnitude of the force exerted on Q by q?

Front

3 N

Back

Batteries Series and Parallels

Front

Battery packs achieve the desired operating voltage by connecting several cells in series; each cell adds its voltage to the total terminal voltage. Parallel connection attains higher capacity for increased current handling; each cell adds to the ampere-hour (Ah) count. Some packs may consist of a combination of series and parallel connections. Laptop batteries commonly have four 3.6V Li-ion cells in series to achieve 14.4V and two in parallel to boost the capacity from 2,400mAh to 4,800mAh. Such a configuration is called 4S2P, meaning four cells in series and two in parallel. Insulating foil between the cells prevents the conductive metallic skin from causing an electrical short. Most battery chemistries lend themselves to series and parallel connection. It is important to use the same battery type with equal voltage and capacity (Ah) and never to mix different makes and sizes. A weaker cell would cause an imbalance. This is especially critical in a series configuration because a battery is only as strong as the weakest link in the chain. An analogy is a chain in which the links represent the cells of a battery connected in series A weak cell may not fail immediately but will get exhausted more quickly than the strong ones when on a load. On charge, the low cell fills up before the strong ones because there is less to fill and it remains in over-charge longer than the others. On discharge, the weak cell empties first and gets hammered by the stronger brothers. Cells in multi-packs must be matched, especially when used under heavy loads.

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Electrostatics Electrical Potential Energy

Front

Symbol: U, Units: J or 1 eV = 1.6x10^-19 J, Energy due to position within an electric field. Energy is conserved, so changes in potential energy often result in changes in either kinetic energy or work done. ΔU = qΔV for all situations U = 1/2QΔV for parallel plates

Back

Which of the following cannot be the units of electric intensity? A. N/C B. I/C-m C. 1/C D. V/m

Front

A. N/C

Back

Energy can be expressed in terms of which unit?

Front

volt

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