added new edits from Irina

1 files changed, 10 insertions, 23 deletions

diff --git a/blackbody_new.tex b/blackbody_new.tex
index 56b3a35..1066c1a 100644
--- a/blackbody_new.tex
+++ b/blackbody_new.tex
@@ -70,10 +70,11 @@ where $c$ is the speed of light and $h=6.626076\times 10^{-34} J\cdot s$ is the
 
 \section*{Radiation sensor operation principle}
 
-\includegraphics[height=2.5in]{./pdf_figs/thermopile} \\
-
-Imagine a metal wire connected to a cold reservoir at one end and a hot reservoir at the other.  Heat will flow between the ends of the wire, carried by the electrons in the conductor, which will tend to diffuse from the hot end to the cold end.  Vibrations in the conductor's atomic lattice can also aid this process. This diffusion causes a potential difference between the two ends of the wire. The size of the potential difference depends on the temperature gradient and on details of the conductive material, but is typically in the few 10s of $\mu V/ K$. A thermocouple, shown on the left, consists of two different conductive materials joined together at one end and connected to a voltmeter at the other end. The potential is, of course, the same on either side of the joint, but the difference in material properties causes $\Delta V=V_1 - V_2 \neq 0$. This $\Delta V$ is measured by the voltmeter and is proportional to $\Delta T$.  Your radiation sensor is a thermopile, simply a ``pile'' of thermocouples connected in series, as shown at the right. This is done to make the potential difference generated by the temperature gradient easier to detect. 
-\\
+Imagine a metal wire connected to a cold reservoir at one end and a hot reservoir at the other.  Heat will flow between the ends of the wire, carried by the electrons in the conductor, which will tend to diffuse from the hot end to the cold end.  Vibrations in the conductor's atomic lattice can also aid this process. This diffusion causes a potential difference between the two ends of the wire. The size of the potential difference depends on the temperature gradient and on details of the conductive material, but is typically in the few 10s of $\mu V/ K$. A thermocouple, shown on the left, consists of two different conductive materials joined together at one end and connected to a voltmeter at the other end. The potential is, of course, the same on either side of the joint, but the difference in material properties causes $\Delta V=V_1 - V_2 \neq 0$. This $\Delta V$ is measured by the voltmeter and is proportional to $\Delta T$.  Your radiation sensor is a thermopile, simply a ``pile'' of thermocouples connected in series, as shown at the right. This is done to make the potential difference generated by the temperature gradient easier to detect.
+\begin{figure}
+\includegraphics[height=1.5in]{./pdf_figs/thermopile}
+\caption{\label{sensor}\emph{Left}: thermocouple construction; \emph{right}: thermopile - an array of thermocouples connected in series.}
+\end{figure} \\
 \textbf{Important}: When using the thermal radiation sensor, make each reading quickly to keep the sensor from heating up. Use sheets of white isolating foam (with the silvered surface facing the lamp) to block the sensor between measurements.
 \\
 \textbf{Sensor calibration}: To obtain the radiation sensor readings for radiated power per unit area $S$ in the correct units ($W/m^2$), you need to use the voltage-to-power conversion factor $22~V/W$, and the area of the sensor $2mm\times2mm$:
@@ -90,7 +91,6 @@ Lamp, Power supply.
 
 Before starting actual experiment take some time to have fun with the thermal radiation sensor. Can you detect your lab partner? What about people across the room? Point the sensor in different directions and see what objects affect the readings. \textbf{These exercises are fun, but you will also gain important intuition about various factors which may affect the accuracy of the measurements!}
 
-
 \begin{enumerate}
 \item  \textbf{Before turning on the lamp}, measure the resistance of the filament of the Stefan-Boltzmann lamp at room temperature. Record the room temperature, visible on the wall thermostat.
 
@@ -100,26 +100,13 @@ Before starting actual experiment take some time to have fun with the thermal ra
 % Resistance of filament (room temperature)=&$\underline{\hskip .7in}$
 %\end{tabular}
 
-\item Connect a multimeter as voltmeter to the output of the power supply.
-	{\bf Important:} make sure it is in the {\bf voltmeter mode}.
-	Compare voltage readings provided by the power supply and the multimeter and verify that their readings are reasonably close. 
-	Which one is the correct one? Think about your measurement
-	uncertainties.
-
-\item Set up the equipment as shown in Fig. \ref{bbht}. VERY IMPORTANT:
-	make all connections to the lamp when the power is off. Turn the
-	power off before changing/removing connections. The voltmeter
-	should be directly connected to the binding posts of the
-	Stefan-Boltzmann lamp. In this case the multimeter voltmeter has
-	direct access to the voltage drop across the bulb, while the power
-	supply voltmeter reads an extra voltage due to finite resistance of
-	the current meter. Compare readings on the multimeter and the power
-	supply current meters. Are they reasonably close? 
+\item To indirectly measure the temperature of the filament, we will use the known dependence of its resistance on the temperature, given in Table.\ref{w_res:fig}. To ensure the accurate measurement, we will again use the four-point probe method (review the video on the course web site, if you need a refresher) by measuring the voltage drop across the lamp. VERY IMPORTANT:
+	make all connections to the lamp when the power is off, and ask the instructor to check your connections before proceeding.
 
 \item Place the thermal sensor at the same height as the filament, with the front face of the sensor approximately 5~cm away from the filament and fix their relative position. Make sure no other objects are viewed by the sensor other than the lamp.
 %
 \item  Turn on the lamp power supply. Set the voltage, $V$, in steps of 1-2
-	volt from 1-12 volts. At each $V$, record the current running through the lamp and the voltage from the radiation sensor.
+	volt from 1-6 volts. At each $V$, record the current running through the lamp and the voltage from the radiation sensor.
 	Calculate the resistance of the lamp using Ohm's Law and determine
 	the temperature $T$ of the lamp from the table shown in Fig.
 	\ref{w_res:fig}. Don't forget to convert the measured temperatures to Kelvin scale: $T[K]=T[^oC]+273$.
@@ -190,10 +177,10 @@ S(r)=\frac{P}{2\pi r^2}
 \newpage
 
 \section*{Universal thermometer}
-Blackbody radiation gives us an ability to measure the temperature of remote objects. Have you ever asked yourself how do astronomer know the temperature of stars or other objects many light years away? The answer - by measuring the light they emit and analyzing it using the expressions for the blackbody radiation spectrum. Wein's law Eq.(\ref{weins}) links the wavelength at which the most radiation is emitted to the inverse of the object's temperature, thus the colder stars emit predominantly in red (hence the name ``red giants''), while emission pick for hot young stars  is shifted to the blue, making them emit in all visible spectrum.
+Blackbody radiation gives us an ability to measure the temperature of remote objects. Have you ever asked yourself how do astronomer know the temperature of stars or other objects many light years away? The answer - by measuring the light they emit and analyzing its spectrum conposition using the expressions for the blackbody radiation spectrum. Wein's law Eq.(\ref{weins}) links the wavelength at which the most radiation is emitted to the inverse of the object's temperature, thus the colder stars emit predominantly in red (hence the name ``red giants''), while emission pick for hot young stars  is shifted to the blue, making them emit in all visible spectrum.
 \includegraphics[height=2.5in]{./pdf_figs/blackbody_radn_curves} 
 
-The human bodies, of course, are much cooler than stars, and emit in infrared range. This radiation is invisible for human eye, but using proper detection method it is possible to create thermal maps of the surroundings with the accuracy better than $1/10$th of a degree. Forward-looking infrared (FLIR) cameras have wide range of applications, from surveillance and military operations to building inspection and repairs, night-time navigation and hunting.  As I write this in Fall 2020, in the middle of COVID19 pandemic, more and more locations use such sensors to measure visitors' temperature at the entrance of a building or a check points in the airports.  
+The human bodies, of course, are much cooler than stars, and emit in infrared range. This radiation is invisible for human eye, but using proper detection methods it is possible to create thermal maps of the surroundings with accuracy better than $1/10$th of a degree. Forward-looking infrared (FLIR) cameras have wide range of applications, from surveillance and military operations to building inspection and repairs, night-time navigation and hunting.  As I write this in Fall 2020, in the middle of COVID19 pandemic, more and more locations use such infrared sensors to measure visitors' temperature at the building entrances or the check points in airports.  
 
 \end{document}