Science and Confidence

(Courtesy of NTDTV)

This video has a lot of good information about some Nobel prize-winning research and talks about how he became interested in science and some of the bumps along the way.

Football? That's physics, too!

In honor of this weekend's Super Bowl, here are a few videos about the physics of football.

(Courtesy of Yale University)

Courtesy of University of Minnesota

Courtesy of SEC Digital Network

Have a great weekend!

Doh! What is doping? Why do we "dope" semiconductors?

Doping is when you intentionally add impurities to a material. Why, then, after going to the trouble to purify the material do you purposely undo your good work? Dopants change the electronic properties of a material. In any material, you can only have electrons at certain energies. These energies, in condensed matter (liquids and solids), are typically found in bands, or ranges, of allowed energies.

In a semiconductor, you have a gap between energy states that likely have electrons in them (valence band) and energy states that likely don't have electrons in them (conduction band). Thermal energy makes it so that there is a likelihood (relatively small) of finding an electron in the conduction band although, if all states were filled from the lowest energy on up, there would be no electrons in the conduction band. Dopants add or remove electrons from the mix, either increasing or decreasing the likelihood of finding electrons in the conduction band. P-type dopants make there be fewer electrons than a semiconductor (like silicon) without these dopants. N-type dopants make there be more electrons than a semiconductor without these dopants. The electrons in the conduction band and the missing charges, or holes, in the valence band allow charge to flow when a voltage (electric potential) is applied. Check out this interactive demonstration to see how doping changes carrier concentrations and allows charge to flow! If you have difficulty viewing this, download this software (http://www.wolfram.com/cdf-player/).

Doped Silicon Semiconductors from the Wolfram Demonstrations Project by S. M. Blinder

The energy above and below which you are equally likely to find an electron at temperatures above absolute 0 K is called the Fermi level. This can be found within the energy gap or within a band although, in semiconductors, it is typically somewhere in the gap.

Brr, It's Cold Outside. What is temperature and how do we measure it?

Intuitively, temperature is a scale that describes how hot things are. According to thermodynamics and math, however, it is a bit more complicated. I will mention this definition in the comments section. We will go with the working definition: how much heat is in an object, or the amount of kinetic energy of particles in that object. When you see a weather forecast, you typically see temperature measured in Fahrenheit (°F). Water freezes at 32 °F and boils (at atmospheric pressure) at 212 °F. Another commonly used temperature scale is the Celsius scale (°C). In this system, water freezes at 0 °C and boils (at atmospheric pressure) at 100 °C. These are both relative temperature scales. You may have heard of absolute 0. Absolute 0 is the lowest energy possible, period. This isn't the 0 that your weatherman talks about. A more useful scale would begin at this temperature. Some examples of these scales include the Rankine (R) and Kelvin (K) scales, related to the Fahrenheit and Celsius scales, respectively. 459.67 R is equivalent to 0  R and 0 °F, with the same scale interval, and 273 K is equivalent to 0 °C, with the same scale interval.

How do we measure temperature? There are many ways. Many thermometers that you may have seen work by enclosing a liquid in a glass bulb and measuring the expansion of that liquid volume with temperature by seeing how far up a narrow tube the liquid volume extends. Such a liquid should expand significantly when heated. A pyrometer measures temperature (typically high-temperatures) by investigating the electromagnetic radiation (visible and invisible light) that is given off by all matter. This is called black-body radiation. This power given off by the material is absorbed by a material in the detector. Knowing the geometry of the setup, it is possible to relate the absorbed power to the object temperature by the following equation, where P_radiated is the power radiated, ε is a material constant called emissivity, σ_S is a constant, A is the radiating area, and T is temperature:

P_radiated=εσ_SAT⁴

This technique has the added bonus that you do not need anything to touch the thing that you are measuring.

Thermocouples can also measure temperature. A thermocouple has 2 wires made of different metals, attached together. One junction (where the 2 wires come together) is placed at the place that you want to measure the temperature and the other junction is placed at a known temperature. The voltage is measured (in series) at a point between the hot and cold ends. That voltage can be related to the temperature of the unknown junction. Try playing with this applet to see how the Seebeck coefficient and temperature affect the voltage measured. The Seebeck coefficient is a proportionality constant that relates the voltage developed across the wires to temperature. If you are having difficulty using this applet, download the player here.

Seebeck Effect in a Thermocouple from the Wolfram Demonstrations Project by Andrew Tuzhykov

Meet the Researchers: Professor Lisa McElwee-White

Have you ever wanted to talk to and meet a scientist? We wanted to introduce ourselves to our readers. Please ask us a question/share ideas using the form on the left side of the page.

Professor McElwee-White recently was interviewed by ACS. Check it out by following this link.

Goal!!! Hockey Science: It's Just Physics

Comic from XDCD comic 669 (Link not included, since not all comics contain language appropriate for children)

Skaters race around the rink, colliding while trying to make goals. It is hard to find a more exciting fast-paced sport than hockey (maybe I'm biased). At a match, physics is often the last thing on your mind. However, the game really is just physics. The ice nearly becomes that infamous frictionless surface. Hockey is a physics playground. Check out this (the San Francisco Exploratorium) site to learn more about the physics of hockey.

This video also talks about the physics of hockey. It also talks about ice thermodynamics, a topic related (the thermodynamics part) to what we study. Thermodynamics is the study of how energy is transferred.

Video from University of Michigan News Service

Puzzlers: Let's not go into that other wild blue yonder. Save the planes!

Microsoft Clip Art Image 

Note: This post takes its inspiration from a puzzler on the radio show Car Talk on NPR aired 8/21/06. Car Talk hosts weekly puzzlers that are often car or math-related.

Your country is at war and your planes keep on being shot down. You are called in to determine what parts of the plane to reinforce and make impenetrable to bullets. You can look at all the planes that have been shot at and returned to base. Assuming shots at the plane were distributed evenly around the plane, what do you look for to tell you where to reinforce?

How is this relevant? Engineers are called in to both design things and fix them when they break. We must be able to target parts of a product for improvement and balance the cost of that improvement with the benefit that the improvement provides. Science researchers also must first identify a problem and look at evidence that may lead to a solution.

Similarly to this problem, sometimes scientists study things that they cannot directly see. They can only see the effects of the phenomena on a limited set of data. It is important to be able to make sense of the data and obtain from it all that is possible.

Note: the answer is in the comments.