Kinetic and Potential Energy
Investigation 2 – Concept Day
Kinetic and Potential Energy: Investigation 2
- In this Investigation we will continue to study the Law of Conservation of Energy: energy is neither created nor destroyed; it simply changes form.
- We will focus on the concept of changing forms of energy by exploring the conversion of electrical energy to light and thermal energy.
Note: The basic experiment in the Lab for Investigation 2 is to use several different wattage incandescent light bulbs and determine the amount of light and heat they produce. In the process of conducting these experiments, however, you should appreciate that electrical, light, and thermal energy are all forms of kinetic energy, the energy of movement. This will be summarized for you in the second to last slide (KINETIC-2-8) below.
Note: Finally, since you may not know how an incandescent light bulb works, we take this opportunity to introduce you to this simple and magnificent invention that changed the world. It is also important for you to understand how the light bulb works for you to appreciate the energy conversions involved in its operation.
- There is extreme power associated with electrical kinetic energy.
Note: Lightning is perhaps the most powerful, regularly occurring natural phenomena recognized by most people.
- The electrical energy of lightning is converted to three very obvious other forms of energy, light, heat, and sound (thunder).
Note: This slide is included to remind you of what electrons are and that they exhibit kinetic energy in a completed circuit.
- Batteries are a storehouse of electrical energy as they are a source of electrons that can leave and enter a circuit they are attached to.
Note: The electrons in batteries are generated by controlled chemical reactions within the battery. When the chemicals required to produce the electrons are used up, no more electrons are produced and the battery is said to be “dead”.
- Notice that the electrons leave the battery at the minus (-) terminal and are redirected back to the positive (+) terminal.
- The negatively charged electrons always move toward positive and away from negative charges.
Note: In the experiments you will perform in Lab in Investigation 2, you will not use batteries but rather wall current. Nonetheless, you will still be working with a current of negatively charged electrons.
- This slide shows the anatomy of an incandescent light bulb. The very thin and long tungsten wire gets incredibly hot (over 2,000oC!) because of the flow of electrons through it.
- The more electrons that flow through a light bulb in a period of time, the hotter and brighter it will get.
- For example, a dimmer switch controls the amount of electrons that flow through a light bulb. As the switch is turned up, more electrons flow through the tungsten coil and it gets hotter and brighter.
Note: In the Lab for Investigation 2, you will directly measure these differences. Not by using a dimmer switch, but by using several different wattage incandescent light bulbs, each of which has differing amounts of electrons that flow through the tungsten wire.
- Finally, notice that while the tungsten metal does not melt at operating temperatures, it would burst into flames if heated so high outside the bulb, in the presence of oxygen.
- To avoid this combustion, in the “old days” light bulbs were manufactured to hold a vacuum, thus eliminating oxygen from the area around the glowing metal.
- This created its own problems and more modern light bulbs are not produced with a vacuum but rather the air (containing ~21% oxygen) is replaced with an “inert” gas like argon (element 18 in the Periodic Table of the Elements).
- Argon can not substitute for oxygen in a combustion reaction. This allows the tungsten metal to glow at exceedingly high temperatures but not ignite and burst into flames.
- Anyone that has witnessed the breaking of a burning light bulb may recall a small puff of smoke when the bulb shatters. This is from the combustion of the tungsten wire in the presence of atmospheric oxygen.
- This slide simply shows the flow of electrons from a light socket into, through, and out of an incandescent light bulb.
- Looking at the two terminals in the empty socket (center), one can easily see the danger involved in placing one’s finger into this area.
- Skin contact made between the two terminals causes a complete circuit, just as if a bulb were screwed into the socket. Thus, the kinetic energy of moving electrons will move through the body in much the same way as they would through a bulb, causing significant tissue damage in the process.
- Electrons must come from somewhere.
- In experiments using batteries, the source of electrons is often easier to visualize.
- Insert the battery, electrons begin to flow and a light bulb glows.
- Remove the battery and the light bulb goes out because there are no longer any electrons flowing to make it glow.
- Most electricity we use in our houses is produced at a distance from us. Nonetheless, it is nothing more than a source of electrons.
- When we plug an appliance into the wall at home, we create a circuit and permit electrons to flow through the device.
- The electrons flow through a wire and into the appliance.
- In a similar manner, electrons flow through a wire from their source of production at a power plant.
- Regardless of how the power is harnessed (solar, gas, coal, hydroelectric, wind, nuclear, etc.), the power reaches our homes and schools as a current of electrons and becomes available in a controlled manner from electrical “outlets”. When we plug an electrical cord into an outlet, we cause electrons to move and use their kinetic energy.
Note: Now that you understand how a light bulb produces light and heat from electrical energy, we can begin to focus on the lab experiment for Investigation 2.
Note: This slide introduces the units in which you will record/report energy measurements.
- Electrical energy will be measured in watts.
- A watt is defined as one joule per second.
- We will not measure wattage, but rather use the wattage designation stamped on the light bulbs.
- Light will be measured in a unit known as the lux.
- This is a measure of the amount of illumination per unit of surface area.
- We can measure lux with a light meter.
- Finally, we will measure temperature, as usual, in degrees Celsius (oC) with a glass thermometer.
- All kinetic energy is the energy of movement.
- Electrical kinetic energy represents the movement of electrons.
- Light kinetic energy is the movement of photons.
- Heat or thermal kinetic energy represents the movement of molecules.
Note: you are unlikely to have a good understanding of photons at this point. They are exceeding small particles and you will learn more about them in time.
- This slide depicts some of the potential dangers in the Lab for Investigation 2.