Transcript Batteries
Batteries • • • • • • 3 Parts: Cathode (positive charge), anode (negative charge) and an electrolyte (substance with free ions (positively charged atoms) Reactions occur at the anode which release electrons, they want to flow toward the cathode. But the electrolyte keeps the electrons from flowing to the cathode. If you create a closed circuit, and provide the electrons an alternate path to flow to the cathode, then they will follow that path. Now the chemical reactions at the anode change the anode and the electrolyte chemical composition, and eventually they can no longer occur. So the battery no longer produces electrons and current. When you recharge a battery ,you reverse the flow of electrons through the battery and reverse the the chemical process, restoring the battery to almost its original chemical state. Earliest batteries-Baghdad battery • Also called the Parthian Battery • Artifacts discovered in 1936 near Baghdad. • Terracotta jar 5 inches tall, containing a copper rolled up copper sheet housing a single iron rod. • If it were filled with an acidic liquid, it could produce a current • Use as a battery is uncertain, many different interpretations exist. Leyden Jars • Device that stores static electricity • Earliest form of what we now call a capacitor • Glass jar with metal foil coating the inner and outer surfaces. A rod is connected to the inner foil and sticks out of the mouth of the jar. • Need to be initially charged Galvanic Cells • First attempt to derive energy from chemical reactions • Consists of two metals (often copper and zinc) in a solution of a salt of the metal, connected by a salt bridge (really just a porous plate) • Also called voltaic cells or electrochemical cells Voltaic pile • First true electric battery • Alessandra Volta first showed that when copper and zinc discs are separated by cardboard soaked in brine, they act as a galvanic cell. • He further showed that if you stack several pairs of these, you get a current to flow. Inside a modern battery Leaky batteries • • • • • • Alkaline batteries-popular form of battery for many devices Uses potassium hydroxide, which is an alkaline as the electrolyte, instead of ammonium chloride or zinc chloride. All three are acids and can corrode the outer steel shell and leak. In addition, as a battery is discharged, Hydrogen as is formed, which increases the pressure inside the battery. This can rupture the seals on the ends of the battery or the battery canister itself. They create a crystalline structure on the outside of the battery. It can cause oxidation on copper leads and damages circuits. A solution of water and baking soda or vinegar can be used to attempt to clean corroded contacts. Lithium ion batteries • In these batteries, lithium ions are extracted from the anode and inserted into the cathode to create a current. • The electrolyte is often a lithium salt in a solution of ethylene carbonate • Note: a lithium battery is a different battery, it has a lithium anode-these have a longer lifetime and can produce higher currents and voltages. Heat Energy Energy associated with the random motions of the molecules in a medium. Measured by temperature • Temperature Scales: • Fahrenheit – based on the height of liquid (often mercury or alcohol) in a glass tube. • Celsius – another scale using height of liquid in a tube • Kelvin-absolute scale – True measure of energy Fahrenheit temperature scale • Freezing point of water set at 32 and boiling point set at 212, so there is 180 degrees between them and each degree is 1/180 of the difference between these two points. Celsius temperature scale • Freezing point of water set at 0 and boiling point set at 100, so there is 100 degrees between them and each degree is 1/100 of the difference between these two points. Kelvin temperature scale • O k is absolute zero. All molecular motion stops. • Interval set so that 1 k = 1 c • So to convert from c to k k=c+273 Mass Energy • E = mc2 • Energy and mass are equivalent • C = 3 x 108 m/s. • A big number and its squared! So even if m is small, E is big. • A small mass, converted to energy, gives a lot of energy! Example Electromagnetic energy •Light displays properties of both waves and particles. •Light is an electromagnetic wave-a wave created by alternating electric and magnetic fields. •“Light” is more than just visible light, it covers wavelengths from radio thru Gamma rays •Light is also a “particle” called a photon. •Photons have energy given by E=hν or E=hc/λ. H is constant, c is the speed of light , ν is the frequency of light and λ is the wavelength of the light. Conservation of Energy • The principle of conservation of energy states that energy cannot be created or destroyed. But it can be converted from one form to another • This idea of energy transformation is at the heart of energy generation. Energy Sources renewable vs nonrewnewable • Renewable – can’t be exhausted • Solar • Geo-thermal • Tidal • Wind • Hydro • Non-renewable-can be exhausted • Fossil fuels (oil, coal etc) uranium How much do we use? • World energy consumption • US energy consumption How much do we use? How much do we use? • Almost 95% of the energy we use comes from non-renewble energy sources! • One of these days we will run out, and then what? • What are some short and long term answers to this question?