If the reaction was to occur without this separation, energy in the form of heat would be released and the battery would not be effective. Figure 1: A Zinc-Copper Voltaic cell. The voltaic cell is providing the electricity needed to power the light-bulb. Types of Batteries Figure 2: Primary versus Secondary Batteries. Primary batteries (left) are non-rechargeable and disposable. Secondary batteries (right) are rechargeable, like this cellular phone battery. Primary Batteries Primary batteries are non-rechargeable and disposable. The electrochemical reactions in these batteries are non-reversible. Primary batteries can lose around 8% to 20% of their charge over the course of a year without any use. This is caused by side chemical reactions that do not produce current. The rate of side reactions can be slowed by lowering temperature. Warmer temperatures can also lower the performance of the battery, by speeding up Current, as the name implies, is the flow of electrical charge. Voltage is how much current can potentially flow through the system. Figure 4 illustrates the difference between current and voltage. Figure 4: The difference between voltage and current. Water is flowing out of a hose and onto a waterwheel, turning it. Current can be thought of as the amount of water flowing through the hose. Voltage can be thought of as the pressure or strength of water flowing through the hose. The first hose does not have much water flowing through it and also lacks pressure, and is consequently unable to turn the waterwheel very effectively. The second hose has a significant amount of water flowing through it, so it has a large amount of current. The third hose does not have as much water flowing through it, but does have something blocking much of the hose. This increases the pressure of the water flowing out of the hose, giving it a large voltage and allowing the water to hit the waterwheel with more force than the first hose. Standard reduction potential, E o , is a measurement of voltage. Standard reduction potential can be calculated with the knowledge that it is the difference in energy potentials between the cathode and the anode : E o cell = E o cathode − E o anode . Different Sizes of Batteries and Some Additional Facts Batteries vary both in size and voltage due to the chemical properties and contents within the cell. However, batteries of different sizes may have the same voltage. The reason for this phenomenon is that the standard cell potential does not depend on the size of a battery but rather on its internal content. Therefore, batteries of different sizes can have the same voltage (Figure 5). Additionally, there are ways in which batteries can amplify their voltages and current. When batteries are lined up in a series of rows it increases their voltage, and when batteries are lined up in a series of columns it can increases their current. Figure 5: Four batteries of different sizes all of 1.5 voltage Hazards Batteries can explode through misuse or malfunction. By attempting to overcharge a rechargeable battery or charging it at an excessive rate, gases can build up in the battery and potentially cause a rupture. A short circuit can also lead to an explosion. A battery placed in a fire can also lead to an explosion as steam builds up inside the battery. Leakage is also a concern, because chemicals inside batteries can be dangerous and damaging. Leakage emitted from the batteries can ruin the device they are housed in, and is dangerous to handle. There are numerous environmental concerns with the widespread use of batteries. The production of batteries consumes many resources and involves the handling of many dangerous chemicals. Used batteries are often improperly disposed of and contribute to electronic waste. The materials inside batteries can potentially be toxic pollutants, making improper disposal especially dangerous. Through electronic recycling programs, toxic metals such as lead and mercury are kept from entering and harming the environment. Consumption of batteries is harmful and can lead to death. Homemade Batteries Any liquid or moist object that has enough ions to be electrically conductive can be used to make a battery. It is even possible to generate small amounts of electricity by inserting electrodes of different metals into potatoes, lemons, bananas, or carbonated cola. A voltaic pile can be created using two coins and a paper dipped in salt water. Stacking multiple coins in a series can results in an increase in current. Practice Problems Problems 1. Yes/No Will adding batteries that are lined up in a row amplify the overall voltage of the batteries? Do electrolytic cells undergo non-spontaneous chemical reactions? Are rechargeable batteries also known as disposable batteries? Can batteries of different sizes have the same voltage? 2.

[2] Polystyrene film capacitors This type of capacitor is not for use in high frequency circuits, being made with a coil inside. They can charge and discharge even more quickly than other capacitors. They are used in filter circuits or timing circuits which run at several hundred KHz or less. Electrolytic capacitors Electrolytic capacitors use a conducting surface inside a liquid electrolyte. They do not charge and discharge as rapidly as film capacitors do. They have polarity and so they have to be attached correctly. There are two leads; one will have a + and the other a -. This means one lead is positive and one is negative. There are two different styles: axial, where the leads are connected to each end, and radial, where the leads are connected to one end. Electrolytic capacitors are printed with capacitance and voltage rating. Since the voltage rating can be low, it is important to check that the electrolytic capacitor is not overcharged. Capacitors can be separated from a battery, then connected in series. Because the capacitor is polarized, the positive terminal must be connected to a negative terminal. Capacitors are combined in series to achieve a higher working voltage, for example for smoothing a high voltage power supply. The voltage ratings, which are based on plate separation, add up, if capacitance and leakage currents for each capacitor are identical. In such an application, on occasion, series strings are connected in parallel, forming a matrix. The goal is to maximize the energy storage of the network without overloading any capacitor. For high-energy storage with capacitors in series, some safety considerations must be applied to ensure one capacitor failing and leaking current does not apply too much voltage to the other series capacitors. Series connection is also sometimes used to adapt polarized electrolytic capacitors for bipolar AC use. Electrolytic capacitors use an aluminum or tantalum plate with an oxide dielectric layer. The second electrode is a liquid electrolyte, connected to the circuit by another foil plate. Electrolytic capacitors offer very high capacitance but suffer from poor tolerances, high instability, gradual loss of capacitance especially when subjected to heat, and high leakage current. Poor quality capacitors may leak electrolyte, which is harmful to printed circuit boards. The conductivity of the electrolyte drops at low temperatures, which increases equivalent series resistance. While widely used for power-supply conditioning, poor high-frequency characteristics make them unsuitable for many applications. Electrolytic capacitors suffer from self-degradation if unused for a period (around a year), and when full power is applied may short circuit, permanently damaging the capacitor and usually blowing a fuse or causing failure of rectifier diodes. For example, in older equipment, this may cause arcing in rectifier tubes. They can be restored before use by gradually applying the operating voltage, often performed on antique vacuum tube equipment over a period of thirty minutes by using a variable transformer to supply AC power. The use of this technique may be less satisfactory for some solid state equipment, which may be damaged by operation below its normal power range, requiring that the power supply first be isolated from the consuming circuits. Such remedies may not be applicable to modern high-frequency power supplies as these produce full output voltage even with reduced input. Tantalum capacitors offer better frequency and temperature characteristics than aluminum, but higher dielectric absorption and leakage. Polymer capacitors (OS-CON, OC-CON, KO, AO) use solid conductive polymer (or polymerized organic semiconductor) as electrolyte and offer longer life and lower ESR at higher cost than standard electrolytic capacitors. A feedthrough capacitor is a component that, while not serving as its main use, has capacitance and is used to conduct signals through a conductive sheet. Several other types of capacitor are available for specialist applications. Supercapacitors store large amounts of energy. Supercapacitors made from carbon aerogel, carbon nanotubes, or highly porous electrode materials, offer extremely high capacitance (up to 5 kF as of 2010) and can be used in some applications instead of rechargeable batteries. Alternating current capacitors are specifically designed to work on line (mains) voltage AC power circuits. They are commonly used in electric motor circuits and are often designed to handle large currents, so they tend When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay. If the inductance is large enough, the energy may generate a spark, causing the contact points to oxidize, deteriorate, or sometimes weld together, or destroying a solid-state switch. A snubber capacitor across the newly opened circuit creates a path for this impulse to bypass the contact points, thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance. Similarly, in smaller scale circuits, the spark may not be enough to damage the switch but may still radiate undesirable radio frequency interference (RFI), which a filter capacitor absorbs. Snubber capacitors are usually employed with a low-value resistor in series, to dissipate energy and minimize RFI. Such resistor-capacitor combinations are available in a single package. Capacitors are also used in parallel with interrupting units of a high-voltage circuit breaker to equally distribute the voltage between these units. These are called "grading capacitors". In schematic diagrams, a capacitor used primarily for DC charge storage is often drawn vertically in circuit diagrams with the lower, more negative, plate drawn as an arc. The straight plate indicates the positive terminal of the device, if it is polarized (see electrolytic capacitor).