Schlieren imaging is a fascinating technique that lets us see tiny differences in the air, like changes in temperature, pressure, and composition. This method can reveal cool things, like the heat waves from a lit match. In this article, we’ll clear up some common questions about the Schlieren setup and share some exciting experiments inspired by viewer suggestions.
A big point of confusion was about the type of mirror used in the setup. I called it a parabolic mirror, but also mentioned it could be part of a sphere. While a parabolic shape isn’t part of a sphere, the small size of the mirror makes the two shapes quite similar. So, a parabolic concave mirror works well as an approximation for a spherical concave mirror in this context.
Another common question was about the light source used in Schlieren imaging. Some shots were captured at an impressive 2,000 frames per second using just a tiny LED. Initially, I was worried about generating enough light, so I used powerful flashlights as my main light source. The focal length of my mirror is 1.8 meters, meaning light converges at the center of curvature, which is 3.6 meters back. This setup allows the reflected light to form a bright spot, even in daylight.
To show the Schlieren effect, I placed an object in front of the mirror. The initial image wasn’t great, so I covered the light source with tin foil and made a small hole to reduce its size. This adjustment decreased brightness but enhanced the flaring effect, making it easier to capture a bright image.
A key part of the Schlieren setup is the razor blade, which helps increase image contrast. The differences in refractive index we observe are tiny, causing light to deflect slightly. By using the razor blade to cut off part of the bright spot, we can enhance the visibility of the deflected light, improving image quality.
Some viewers suggested using colored filters instead of a razor blade. I tried two different colors of cellophane, positioning them so the focal point was in the middle. This setup allowed some light to pass through one color while other light passed through the second color. When I placed a transparent helium balloon in front of the mirror, the slight deflection of light made the balloon appear a different color. After popping the balloon, the helium remained visible in the shape of the balloon for a brief moment.
One viewer suggested lighting a barbecue lighter with a match. I demonstrated this by releasing gas and allowing the flame to travel through it, capturing the Schlieren effect as the flame ignited.
Another intriguing idea was to light a ping-pong ball on fire. High-quality ping-pong balls are quite flammable, so I tried it out. The result was visually striking, showcasing the flames in action.
Many viewers were interested in visualizing sound, like the shock wave from a clap. Despite multiple attempts, capturing the shock wave was challenging, even at high frame rates. The speed of sound is over 300 meters per second, making it hard to capture more than a couple of frames that include the shock wave. However, I did manage to observe the air being pushed out from between my fingers during a clap, although this wasn’t the actual sound wave.
Thanks to everyone who contributed suggestions for Schlieren imaging experiments. If you have more ideas, feel free to leave them in the comments. I look forward to exploring these concepts further, although it may take some time to respond as I will be traveling to Australia soon. This journey will provide an opportunity to reflect on the fascinating intersection of science and creativity that Schlieren imaging represents.
Gather materials to create a basic Schlieren imaging setup. Use a concave mirror, a light source, and a razor blade. Experiment with different objects to observe the Schlieren effect. Document your observations and explain how the setup reveals changes in air density.
Test various light sources, such as LEDs and flashlights, in your Schlieren setup. Compare the clarity and brightness of the images produced. Discuss how the choice of light source affects the visibility of Schlieren patterns and the importance of focal length in your setup.
Use your Schlieren setup to visualize temperature changes. Hold a lit match or a warm object in front of the mirror and observe the heat waves. Record your findings and explain how Schlieren imaging can be used to study temperature variations in different environments.
Try using colored filters instead of a razor blade in your Schlieren setup. Experiment with different colors and observe how they affect the visibility of Schlieren patterns. Discuss the advantages and limitations of using colored filters compared to the traditional razor blade method.
Attempt to visualize sound waves using your Schlieren setup. Clap your hands or use a small speaker to generate sound waves. Record your attempts and analyze the challenges of capturing sound waves with Schlieren imaging. Discuss the speed of sound and its impact on your observations.
Schlieren – A technique used to visualize changes in fluid density, often used to observe airflows and shock waves. – In the physics lab, we used schlieren imaging to study the airflow patterns around a model airplane wing.
Imaging – The process of creating visual representations of objects or phenomena, often using specialized equipment. – The imaging system allowed us to capture high-resolution images of the diffraction patterns produced by the laser.
Light – Electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. – The experiment demonstrated how light can be refracted when it passes through different media.
Mirror – A reflective surface that redirects light, often used in optical experiments to manipulate light paths. – By adjusting the angle of the mirror, we were able to focus the laser beam precisely onto the target.
Contrast – The difference in luminance or color that makes an object distinguishable from others within the same field of view. – The high contrast in the thermal imaging allowed us to clearly see the heat distribution across the surface.
Deflection – The change in direction of a wave or particle due to a force or obstacle. – The deflection of the electron beam in the magnetic field was measured to determine the charge-to-mass ratio of the electron.
Temperature – A measure of the average kinetic energy of the particles in a substance, indicating how hot or cold the substance is. – As the temperature of the gas increased, its volume expanded according to Charles’s Law.
Pressure – The force exerted per unit area on the surface of an object, often measured in pascals (Pa). – The pressure inside the container was calculated using the ideal gas law, $PV = nRT$.
Sound – A type of wave that is created by vibrating objects and propagates through a medium such as air. – The speed of sound in air was determined by measuring the time it took for an echo to return from a distant wall.
Experiments – Scientific procedures undertaken to test a hypothesis, demonstrate a known fact, or discover new phenomena. – The physics experiments conducted in the lab provided valuable insights into the principles of electromagnetism.
