Heat & Thermodynamics
Heat is more than just a sensation—it is energy in motion. In this chapter, we explore how thermal energy is transferred, stored, and transformed in the world around us. Using smartphone tools like thermal cameras, barometers, and infrared sensors, students can visualize the invisible: from convection currents and radiant heat to the cooling power of evaporation and the surprising thermodynamics of stretched rubber. Through real-world materials and clever digital tools, abstract thermodynamic principles become not only tangible but measurable. This chapter invites students to engage directly with the physics of energy—revealing the hidden patterns behind temperature, transformation, and equilibrium.
Temperature, Heat, and Energy Transfer
Infrared Thermography (HEAT-01)
Sensors Used: Infrared camera (far-infrared), smartphone camera (modified for near-infrared)
What’s Measured: Apparent surface temperature distribution through infrared imaging
Description
Infrared thermography allows us to see heat directly, and some smartphones—such as the CAT S60—come equipped with thermal imaging cameras capable of detecting far-infrared radiation emitted by warm objects. When aimed at a stovetop, this camera reveals the burner heating up well before it begins to glow visibly red. A lingering handprint on a tabletop, the warm breath on a window, or the comparison between heat emitted by a toaster and a hairdryer—these are all made visible through thermographic imaging, offering a striking visualization of heat transfer. Thermal cameras detect radiation in the far-infrared region of the spectrum, which is associated with the actual temperature of surfaces and objects.
This contrasts with standard smartphone cameras, which are sensitive only to visible and near-infrared light. In fact, most phone cameras include infrared-blocking filters to prevent image distortion. However, when these filters are removed—as demonstrated in DIY projects like the one in Reference [1]—a modified webcam or smartphone camera can detect near-infrared light, such as that emitted by TV remotes or sunlight just beyond the red part of the spectrum. Though not sensitive to thermal radiation in the same way as true infrared thermography, these modified cameras offer another route into the hidden world beyond the visible.
References:
[1] “Make an Infrared Camera,” https://www.thenakedscientists.com/get-naked/experiments/make-infrared-camera
Thermal Radiation and Color Absorption (HEAT-02)
Sensors Used: Infrared camera, smartphone camera, thermometer
What’s Measured: Surface temperature differences due to radiation and color-based absorption
Description
This experiment explores how different materials and colors absorb, emit, and reflect thermal radiation—insights that are easily captured using a smartphone equipped with an infrared camera. Begin by observing warm objects such as your hand, a heated mug, or a patch of sunlight on the floor. You’ll notice that matte surfaces tend to glow more brightly in thermal imaging than shiny or reflective ones. This is because matte materials generally have higher emissivity, allowing them to radiate heat more effectively, while shiny metals reflect infrared radiation and appear cooler in thermal images—even if they’re just as hot.
To explore how color affects heat absorption, place black and white sheets of paper side by side in direct sunlight and leave them for a few minutes. Using the infrared camera or a thermometer, measure their surface temperatures. You’ll observe a noticeable difference: the black surface absorbs more sunlight and warms significantly faster than the white one. This phenomenon, rooted in the principles of absorptivity and reflectivity, is not only a staple of thermodynamics but also explains everyday phenomena—such as why white roofs help keep buildings cool or why penguins sport their distinctive tuxedo look for thermal efficiency.
This experiment can be extended further by introducing additional colors or materials—such as aluminum foil, which reflects both visible and infrared light—to compare how their thermal profiles vary under identical lighting conditions. The results offer a vivid, real-world illustration of energy transfer and heat retention, and connect directly to environmental and engineering applications such as solar panel design, passive cooling strategies, and clothing technology.
References:
[1] “Compare different colors’ abilities to absorb light energy,” https://www.youtube.com/watch?v=tATuo3HnCWM
Radiative vs. Convective Heat: Toaster vs. Hairdryer (HEAT-03)
Sensors Used: Infrared camera, thermometer, mirror
What’s Measured: Temperature profiles of objects and air
Description
This experiment is designed to help students distinguish between two major modes of heat transfer: radiation and convection. Using a toaster and a hairdryer—two common household appliances—you can see these principles in action, especially when visualized through a smartphone equipped with an infrared (IR) camera.
Start by turning on the toaster and observing its heating elements. You’ll notice they glow visibly red, but even before this glow becomes apparent to the naked eye, the IR camera reveals a sharp increase in emitted thermal radiation. This radiant heat travels in straight lines and warms only the surfaces directly facing the toaster—this can be tested by placing your hand or a piece of paper at various angles relative to the toaster’s front. The heating is directional and unaffected by air currents, illustrating the line-of-sight nature of thermal radiation.
Now compare this to the hairdryer. Unlike the toaster, the hairdryer emits almost no infrared radiation directly from its nozzle when viewed with an IR camera. Instead, it warms surrounding objects through moving air—convective heat transfer. Hold your hand in the airstream or blow over a surface, and you’ll feel warmth spreading in a more diffused and enveloping manner. The heated air flows around barriers and fills spaces that radiant heat would not reach unless directly exposed. The IR camera will show a gentle warming of the surfaces over time, rather than an immediate glow.
To further distinguish the two modes of heat transfer, try directing both appliances at a surface behind a transparent barrier. Glass, which is transparent to visible light, is opaque to most infrared wavelengths. You’ll find that radiant heat from the toaster is largely blocked by the glass, while the warm air from the hairdryer passes through it with ease. Conversely, plastic wrap or certain acrylics—often transparent to infrared—may allow some radiative heating through, providing a compelling test of material properties.
By combining direct sensation, observation with an IR camera, and simple shielding experiments, students can build a vivid understanding of how heat moves through radiation and convection. The activity not only reinforces abstract textbook concepts but also encourages critical thinking about the everyday thermal environments we live in—from the design of household appliances to architectural insulation.
References:
[1] “Transmitting and absorbing radiant energy,” http://practicalphysics.org/transmitting-and-absorbing-radiant-energy.html
[2] “Conduction, convection and radiation,” http://practicalphysics.org/conduction-convection-and-radiation.html
Evaporation, Capillarity, and Surface Cooling (HEAT-04)
Sensors Used: Thermal (infrared) camera, stopwatch or time-lapse camera
What’s Measured: Temperature variation, evaporation rate, liquid front position
Concepts: Evaporative cooling, capillary action, surface area dependence
Description
This experiment offers a hands-on exploration of how water behaves as it evaporates, spreads, and cools — processes central to thermodynamics, meteorology, and even biology. By combining thermal imaging with time-lapse recording and simple kitchen materials, students can visualize both the physics of phase change and the dynamics of liquid transport through porous media.
Begin with a shallow plate and pour a small, even layer of water onto it. Use a thermal camera — such as the one found in the CAT S60 smartphone — to monitor the surface temperature over time. You’ll notice that the water-covered area is consistently cooler than its dry surroundings. As evaporation proceeds, the temperature can drop by a few degrees due to latent heat loss. Blowing gently over the plate with a fan or hairdryer (set to cool air) will accelerate this process and enhance the temperature gradient. The effect is even more pronounced when the water layer is thin and spread over a large area, highlighting the importance of surface area in evaporation rate.
To explore this relationship more systematically, place identical volumes of water into containers with different surface areas—such as a narrow cup, a wide saucer, and a shallow tray. Record the evaporation progress using a smartphone time-lapse or periodic measurements with a thermal camera. The container with the largest surface area will lose water the fastest, reinforcing the connection between exposed area and evaporation.
Now turn your attention to capillary action and liquid absorption. Dip one end of a paper towel into water and watch as the liquid climbs upward through the fibers. A thermal camera makes this motion even more dramatic: the liquid front appears as a distinct cooler zone advancing through the towel. Compare this with thicker or less porous materials, such as cardstock or a coffee filter. The rate of liquid rise and cooling differs depending on the structure and absorbency of the material. You may also want to try different liquids such as alcohol, for instance.
You can take this one step further by soaking a paper towel in water and holding it vertically. Over time, the water will both rise (via capillary action) and evaporate (from the surface), creating a dynamic balance between transport and cooling. Thermal imaging will show cooler areas near the wet zones, offering real-time insight into heat transfer during evaporation.
Together, these observations paint a vivid picture of how liquids move and cool, revealing the interplay between surface area, phase change, and material properties. From drying laundry to the design of cooling towers, the physics at play here underlies many phenomena in the real world.
References:
[1] “Dependence of Evaporation Rate of Liquid on Liquid Surface Area,” physicsexperiments.eu/1774/dependence-of-evaporation-rate-of-liquid-on-liquid-surface-area
Heating Effects and Transformations
Heating and Cooling Curves with a Thermal Camera (HEAT-05)
Sensors Used: Smartphone thermal (infrared) camera
What’s Measured: Temperature over time
Concepts: Heat transfer, thermal equilibrium, specific heat, phase transitions
Description
With a thermal camera-equipped smartphone like the CAT S60, students can vividly observe how objects heat up and cool down. Place a small item (such as a metal spoon or plastic lid) in hot water or near a radiant heat source for a short time, then move it to a cooler environment and record the temperature change using the thermal camera. The color gradient reveals the temperature profile in real time.
Students can capture images or videos and, with the help of ChatGPT or spreadsheet tools, plot heating and cooling curves to see how temperature approaches equilibrium. Comparing materials highlights differences in thermal conductivity and heat capacity. As an extension, melting ice reveals a temperature plateau during phase change — a direct observation of latent heat.
References:
[1] “Heating and cooling curves,” http://practicalphysics.org/heating-and-cooling-curves.html
Mixing Hot and Cold Water: Exploring Thermal Equilibrium (HEAT-06)
Sensors Used: Infrared (thermal) camera or thermometer
What’s Measured: Final equilibrium temperature
Concepts: Conservation of energy, specific heat capacity, thermal mixing
Description
In this classic experiment, students mix measured quantities of hot and cold water and observe the resulting temperature change. Using a smartphone with a thermal camera (like the CAT S60) or a digital thermometer, they can measure the initial and final temperatures and compare the outcome with theoretical predictions based on conservation of energy.
The thermal camera provides a striking visual representation of the mixing process: warm and cool regions blend into a uniform temperature field, reinforcing the concept of thermal equilibrium. This hands-on activity also invites discussion of heat capacity, thermal energy transfer, and real-world deviations due to heat loss or container insulation.
References:
[1] “Mixing hot and cold water,” http://practicalphysics.org/mixing-hot-and-cold-water.html
Converting Motion into Heat: Impact and Friction Visualized with Infrared (HEAT-07)
Sensors Used: Infrared (thermal) camera
What’s Measured: Temperature increase at point of impact or friction
Description
This experiment demonstrates the transformation of mechanical energy into thermal energy using simple tools and a smartphone with a thermal camera (e.g., CAT S60). Students drop a heavy object such as a book, iron weight, or mallet repeatedly onto a cushion, mattress, or block of jello, and use the camera to observe the temperature increase at the impact site. This visual evidence of localized heating reveals how gravitational potential energy is dissipated as internal energy in the material.
To explore frictional heating, students can walk barefoot on a smooth surface, rub their hands together, or slide a block across a table and immediately capture thermal images of the contact area. In both scenarios, the rise in temperature vividly demonstrates how motion is converted into heat — a core idea in thermodynamics and a tangible introduction to the First Law of Thermodynamics.
References:
[1] “Conversion of Kinetic Energy into Internal Energy: Blow with a Mallet,” physicsexperiments.eu/1706/conversion-of-kinetic-energy-into-internal-energy:-blow-with-a-mallet
Pressure, Temperature, and Boiling in Sealed Systems (HEAT-08)
Sensors Used: Smartphone thermal camera (e.g., CAT S60), onboard pressure and temperature sensors
What’s Measured: Temperature changes, boiling onset, internal pressure variations
Description
This experiment explores how pressure and temperature interact in sealed environments, revealing surprising behavior in gases and liquids. Begin by placing hot water in a vacuum-sealable food container and sealing it tightly. As you use a manual pump to reduce the internal pressure, you’ll observe the water begin to boil — even though it isn’t at 100°C. This striking demonstration shows how the boiling point of a liquid decreases as external pressure drops, a direct consequence of vapor pressure and molecular motion.
In a related setup, place a smartphone equipped with pressure and temperature sensors inside a sealed container. After chilling the container in the fridge, remove it and allow it to warm up in the sun or in a warm water bath. Watch the internal pressure and temperature readings climb as the air inside expands. This offers a direct and intuitive application of the ideal gas law (PV = nRT).
Students can also observe the cooling effect from rapid expansion in aerosol cans — a real-world example of how gases absorb heat as they expand, reinforcing thermodynamic concepts. These simple setups reveal the hidden dynamics of pressure and temperature with clarity and immediacy.
References:
[1] “Vakuum Behälter-Set von VACU NO.1,” https://www.amazon.de/gp/product/B07NNXLCVJ/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Thermal Conductivity and Specific Heat
Exploring Thermal Conductivity with Ice, Metal, and Infrared (HEAT-09)
Sensors Used: Smartphone thermal camera (e.g. CAT S60), video camera
What’s Measured: Melting rate, surface cooling, temperature decay
Description
Thermal conductivity — the ability of a material to transmit heat — can be dramatically visualized with a simple but elegant set of experiments. Begin with the classic “melting race”: place identical ice cubes on slabs of different materials — such as copper, aluminum, ceramic, and wood — and observe which melts the ice the fastest. Your smartphone camera can record a time-lapse video, capturing the changing sizes of the cubes. The rate of melting directly reflects the thermal conductivity of each material, with metals generally leading the race and insulators lagging behind.
To take the investigation further, use your smartphone’s infrared camera to examine how materials retain or shed heat. Heat two wires, one copper and one iron, in hot water or briefly in a flame to equalize their initial temperatures. After removing them from the heat source, observe their cooling behavior with the thermal camera. The copper wire, with its higher thermal conductivity, will shed heat faster than the iron. Similarly, you can place your finger on a mystery surface — metal or plastic — and then remove it. If it’s metal, the heat vanishes rapidly with no lingering “afterglow” on the IR image; if it’s plastic, the warmth lingers, hinting at its poor conductivity.
You can also test more passive heat conduction. Pour hot water into a glass or metal cup, place it on different surfaces (metal foil, cork, ceramic), and after a few minutes, remove it. Watch with the thermal camera to see how the surface below has changed. Some materials will reveal a clear heat imprint — others almost nothing.
Students interested in comparing actual thermal conductivity values can ask ChatGPT for a full table of materials with their respective values in watts per meter-kelvin. This opens the door to not just qualitative observation but quantitative analysis — and the development of real scientific intuition.
References:
[1] “Comparing Thermal Conductivity of Copper, Aluminium and Brass,” physicsexperiments.eu/1769/comparing-thermal-conductivity-of-copper,-aluminium-and-brass
[2] “Ice Cubes Cutting,” physicsexperiments.eu/1943/ice-cubes-cutting
Comparing Heat Capacity of Liquids and Metals (HEAT-10)
Sensors Used: Infrared camera (e.g., CAT S60), thermometer, smartphone timer
What’s Measured: Temperature change over time
Description
Heat capacity — a material’s ability to store thermal energy — plays a crucial role in everything from home insulation to computer cooling systems. In this experiment, students explore and compare the heat capacities of both liquids and solids using smartphone sensors and simple kitchen tools.
Start with two identical containers filled with equal volumes of water and vegetable oil. Expose both to the same heat source — such as placing them under identical lamps or in a warm water bath — and monitor the temperature rise over time using an infrared camera or thermometer. You’ll observe that water heats more slowly than oil. This is a direct manifestation of water’s higher specific heat capacity: it takes more energy to raise its temperature.
Next, shift focus to metals. Select small objects of equal mass — such as screws or nails made of iron, copper, or brass — and immerse them in boiling water until they reach thermal equilibrium (about 100 °C). Then quickly transfer each metal into identical volumes of room-temperature water and measure the temperature increase of the water. The greater the temperature jump, the more energy the metal transferred — indicating it had stored more heat per gram. With guidance or assistance from AI tools like ChatGPT, students can compare their results with tabulated values of specific heat and estimate relative heat capacities.
This experiment illustrates why materials with high heat capacity, like water, are ideal for thermal energy storage, while materials with low heat capacity and high conductivity — like copper — are better suited for transferring heat rapidly, as in radiators or CPU cooling pipes.
This experiment offers both qualitative insights—such as observing that water heats more slowly than oil—and quantitative opportunities. By carefully measuring temperature changes and using known values for mass and specific heat, students can attempt real calculations of heat capacity and energy transfer. While smartphone sensors may introduce some uncertainty, thoughtful experimental design and repeated measurements can yield surprisingly accurate results. Advanced students are encouraged to model the energy exchange and compare their findings to reference data, with support from tools like spreadsheets, graphing apps, or AI-based tutors such as ChatGPT.
Understanding heat capacity is particularly important in real-world contexts: materials with high heat capacity are ideal for thermal storage, while those with low thermal conductivity are better suited for insulation—whether in building design or managing heat flow inside a computer.
References:
[1] Comparing Specific Heat of Water and Vegetable Oil, physicsexperiments.eu/1770/comparing-specific-heat-of-water-and-vegetable-oil
Phase Transitions
Ice and Salt (HEAT-11)
Sensors Used: Thermal camera (e.g., CAT S60)
What’s Measured: Temperature drop, visual change in phase behavior
Description
This classic experiment vividly demonstrates freezing point depression, a key concept in phase transitions. Begin by placing two identical ice cubes side by side and observing them through a thermal camera. Then sprinkle a small amount of salt on one of the cubes. Within seconds, you’ll observe a dramatic temperature drop on the salted cube—often reaching below −20 °C—as the salt dissolves into the surface water and disrupts the lattice structure of the ice. This process lowers the freezing point of water, effectively forcing the ice to melt even as its temperature drops. The same principle is used in de-icing roads in winter. Students can further explore by repeating the test with saltwater mixtures or observing the thermal signature of dry ice (frozen CO₂), which sublimates directly from solid to gas. This hands-on activity provides a striking introduction to colligative properties and energy transfer during phase change.
References:
[1] Cooling Mixture of Water, Ice and Salt, physicsexperiments.eu/2047/cooling-mixture-of-water,-ice-and-salt
Exploring Supercooling and Instant Freezing with Carbonated Beverages (HEAT-12)
Sensors Used: Thermal camera (optional), thermometer
What’s Measured: Onset of freezing, latent heat release
Description
This eye-catching experiment brings supercooling and nucleation to life using nothing more than bottles of carbonated drinks and a salted ice bath. Carefully chill unopened bottles of lemonade, soda, or beer in a slurry of ice and salt. After approximately 90 minutes—just before they begin to freeze—gently remove one bottle. As you twist open the cap, the release of carbon dioxide acts as a nucleation trigger. In an instant, the supercooled liquid crystallizes into a slushy mixture before your eyes. The transformation is not only dramatic but thermodynamically rich: it shows how liquids can exist below their freezing point in a metastable state and how phase transitions can be initiated by mechanical or chemical disturbances. This experiment highlights the concepts of latent heat, nucleation sites, and energy storage in phase change, and is particularly effective for sparking classroom curiosity.
References:
[1] “Freezing lemonade bottles,” https://www.thenakedscientists.com/get-naked/experiments/freezing-lemonade-bottles
Entropy
Heating and Cooling Rubber Bands: Entropy and Elastic Energy (HEAT-13)
Sensors Used: Smartphone infrared camera (e.g., CAT S60)
What’s Measured: Temperature increase during stretching; temperature drop during relaxation
Description
This dual experiment allows students to investigate how rubber bands convert mechanical energy into heat and, inversely, how their relaxation can lead to cooling — a surprising and elegant demonstration of entropy in action. Begin by stretching a rubber band rapidly several times while observing it with a thermal camera. The temperature increase is caused by internal friction and molecular alignment, revealing how mechanical work is transformed into thermal energy. Then, move to the second phase: anchor a rubber band in a stretched position and let it come to thermal equilibrium with the environment. When the rubber band is suddenly released or cut, the molecules return to a more disordered state. This increase in entropy draws thermal energy from the surroundings, creating a localized drop in temperature. Captured via thermal imaging, this cooling effect mimics a solid-state refrigerator and vividly demonstrates the link between elasticity, heat flow, and entropy. This experiment brings to life the surprising thermal behavior of polymers and offers an entry point to non-linear thermodynamics and entropy-driven processes.
Advanced Concepts
Thermal Expansion of Water During Heating (HEAT-14)
Sensors Used: Smartphone camera
What’s Measured: Apparent volume change of water during heating
Description
When a pot of water is heated on the stove, the increase in temperature doesn’t just bring the water to a boil — it causes the liquid itself to expand. Although water is often regarded as incompressible, it does in fact expand measurably with heat, and this expansion can be observed with nothing more than a smartphone and some careful setup.
To begin, fill a transparent container (like a glass measuring cup or tall beaker) with cold water, ideally around room temperature (∼20 °C). Mark the water level with tape or a ruler placed behind the container. Begin heating the water gradually and film the process using your smartphone, either in time-lapse or regular video mode. As the water nears boiling (∼100 °C), you’ll notice the water level rising due to thermal expansion. Avoid stirring during heating to minimize convective distortion, and ensure the container is wide and tall enough to produce a visible rise.
This simple yet striking demonstration makes the concept of thermal expansion tangible and visible, while also reinforcing broader principles of fluid dynamics, temperature, and energy transfer.
Bonus: Estimating the Thermal Expansion Coefficient of Water The volumetric thermal expansion coefficient (β) of water quantifies how much its volume changes with temperature. From the above data this can be calculated.
Bonus: Anomalous Expansion of Water Below 4 °C Unlike most substances, water behaves unusually between 0 °C and 4 °C — it actually contracts as it warms. Water reaches its maximum density at approximately 4 °C; cooling it further causes it to expand again. This anomaly explains why ice floats and why lakes freeze from the top down. While difficult to observe directly in this setup, it’s a fascinating contrast to the expansion behavior demonstrated during heating and a great entry point into discussions of hydrogen bonding, molecular structure, and environmental physics.
Measuring Thermal Expansion of Metals Using Laser Interference (HEAT-15)
Sensors Used: Laser Pointer, Smartphone Camera (or photodiode), Optional Interferometer
What’s Measured: Change in Length via Fringe Shift (micron-scale)
Description
This advanced experiment showcases how laser interferometry can be used to detect extremely small changes in length — such as those caused by heating a metal rod. By incorporating the rod into one arm of a Michelson interferometer, and gently increasing its temperature (for example, using a nearby heat source or resistive wire), students can observe the resulting shift in interference fringes. Each fringe shift corresponds to a specific change in optical path length, allowing for precise quantification of the rod’s expansion down to the micron or even sub-micron scale.
The principle hinges on the fact that, as a material heats up, it expands linearly with temperature according to its thermal expansion coefficient. When this expansion alters the physical length of one of the interferometer arms, it changes the phase relationship between the two beams — producing a visible shift in the interference pattern. By carefully recording the number of fringe shifts and knowing the laser wavelength, students can calculate the change in length and, from there, derive the coefficient of linear expansion for the material under test.
This experiment beautifully unites optics, thermodynamics, and materials science. It reveals not just how materials respond to heat, but also how light can be used as a ruler to detect changes that are otherwise far too small to measure with standard tools. It is ideal for illustrating the sensitivity of interferometry and the practical challenges of high-precision measurement in thermal physics.
Hint: A full Michelson interferometer requires careful optical alignment, but there are clever ways to approximate thermal expansion measurements using a smartphone and a laser pointer. Try asking ChatGPT for help designing a simpler setup!
References:
[1] “Expansion of a solid rod,” http://practicalphysics.org/expansion-solid-rod.html
[2] “Using a Michelson Interferometer to Measure Coefficient of Thermal Expansion of Copper,” https://physlab.org/wp-content/uploads/2016/04/Scholl_liby.pdf
Exploring Blackbody Radiation Through a Dual-Filament Bulb (HEAT-16)
Sensors Used: Smartphone Camera, Lux Meter App, Infrared Camera (optional)
What’s Measured: Luminous Intensity vs. Voltage; Qualitative Heat Transfer
Description
This experiment provides a vivid demonstration of blackbody radiation and its temperature dependence using a simple dual-filament incandescent bulb. In this setup, one filament is actively heated by applying a variable voltage, while the second filament, which remains unpowered, is positioned to receive thermal radiation from the first. As the current through the heated filament increases, its temperature rises, and its emission shifts visibly from a dull red glow to a bright yellow-white light — a direct illustration of Wien’s displacement law.
Using a lux meter app, students can measure the luminous intensity of the emitted light as a function of applied voltage. The light output does not increase linearly, but rather accelerates dramatically at higher temperatures — reflecting the T⁴ dependence of radiated energy described by the Stefan-Boltzmann law. If an infrared camera is available, one can also monitor how the second filament passively warms up due to radiation alone, offering an elegant example of radiative heat transfer between two bodies.
This experiment connects multiple foundational ideas: thermal emission as a function of temperature, the nature of blackbody curves, and the interplay between electrical energy input and radiant output. It also helps clarify the difference between visible light and total radiated energy — a key concept in understanding how different objects “glow” at various temperatures.
The dual-filament bulb setup thus becomes more than a novelty; it transforms into a compact laboratory for exploring radiation, heat, and energy transfer — all visible through the eye of a smartphone.
Blackbody Radiation and Emission Spectra (HEAT-17)
Sensors Used: Smartphone Camera, Diffraction Grating
What’s Measured: Emission Spectra of Light Sources; Qualitative Distribution of Radiated Energy
Description
This experiment explores the principles of blackbody radiation by observing the emission spectra of various common light sources using a smartphone and a simple diffraction grating. In a darkened room, a fragment of a DVD or a dedicated grating is mounted in front of the smartphone camera. Light from sources such as an incandescent bulb, halogen lamp, LED, or a candle flame is directed at the grating, and the resulting spectrum is captured on camera.
When viewing the incandescent and halogen lamps, one should observe a smooth, continuous spectrum, characteristic of blackbody emitters—these sources radiate across a broad range of wavelengths, with intensity depending on temperature. By contrast, LED lights display discrete spectral lines, revealing that they emit at specific wavelengths and are not thermal emitters. A candle flame offers an interesting hybrid: a largely continuous spectrum due to its glowing soot particles, combined with some distinct emission features from excited gas molecules.
Students can analyze the spectral images and qualitatively compare them, relating the observed patterns to the temperature and emission mechanism of each source. These observations offer a hands-on demonstration of Planck’s law and Wien’s displacement law, showing how hotter objects shift their peak emission toward shorter wavelengths. Although not quantitative, the smartphone-based setup vividly illustrates the physical principles behind blackbody radiation and highlights the rich visual differences between thermal and non-thermal light sources.
This simple experiment is an excellent bridge between thermodynamics and optics, demonstrating how temperature governs the light we see—and how even a smartphone can reveal the hidden structure of electromagnetic radiation.
References:
[1] “Black Body Emission,” https://physicsopenlab.org/2015/12/04/black-body-emission/
Capstone / Research Extension
Measuring Boiling Point and Altitude Across Locations (HEAT-18)
Sensors Used: Thermometer, Camera (optional), Barometer (if available)
What’s Measured: Boiling point at different altitudes; atmospheric pressure variation
Description
Boiling water might seem like one of the simplest physical processes — but in fact, it opens a door to a powerful and collaborative investigation of how physics varies across the globe. In this experiment, students measure the boiling point of water at their own location, compare their results with theoretical predictions based on altitude and pressure, and share data with peers from different regions. Together, they build a real-world picture of how environmental conditions influence a supposedly “universal” quantity.
The procedure is simple: bring a small amount of pure water to a rolling boil and record the temperature using a digital thermometer. If your smartphone includes a barometric pressure sensor, you can also log the ambient pressure directly. For comparison, use an online tool such as the Omni Boiling Point Calculator to predict the expected boiling point based on local altitude or pressure. The closer you are to sea level, the nearer your measurement should be to 100 °C; higher altitudes will result in noticeably lower boiling points.
By gathering measurements from classrooms, kitchens, or labs across different cities or countries, students can collaboratively map how boiling point correlates with geography. This experiment doesn’t just make abstract thermodynamic concepts concrete — it also turns science into a shared, distributed effort. With enough participants, even global trends become visible. And best of all, it reminds students that scientific inquiry thrives on communication, comparison, and curiosity that crosses borders.
References:
[1] “Boiling Point Calculator”, https://www.omnicalculator.com/chemistry/boiling-point
Negative Temperatures and Population Inversion: A Conceptual Exploration (HEAT-19)
Sensors Used: None directly; recommended use of videos, animations, and AI tools for simulation
What’s Measured: Not empirical — conceptual understanding
Description
This advanced, discussion-based experiment dives into the counterintuitive realm of negative temperatures and thermodynamic inversion. Students explore how population inversion—where higher energy states are more populated than lower ones—leads to the conditions necessary for laser action and the appearance of “negative Kelvin” temperatures. Using videos and simulations, such as those showing laser excitation or magnetic spin systems, learners engage with the statistical definition of temperature and entropy. This experiment emphasizes that negative temperature does not mean “colder than absolute zero,” but rather, a system where adding energy decreases entropy—flipping the normal thermodynamic rules. Though not a hands-on activity in the traditional sense, this exploration ties beautifully into laser physics, entropy, and the boundaries of classical thermodynamics, offering rich ground for interdisciplinary discussion.