Investigate infrared electromagnetic radiation by using your television remote control as a source and a digital camera as a detector.
Use the infrared remote control to turn the television on and off. How far to the side of the television can you point the remote control and still have it work?
Go into a dark room and point the remote control at your eye. Press the button that turns the television on and off. Can you see the light coming from the bulb in the remote?
Point the remote control at a digital camera and press a button on the remote. Notice that you can see light coming from the bulb on the screen of the camera, but you can’t see it with your naked eye.
Note: You may not see anything if your camera has an infrared light filter. If you are using a mobile device with two cameras and don't see a light, try the front-facing camera, which is less likely to have a filter.
Place a clear piece of glass or plastic between the remote and the camera. Use the camera to look at the remote while you press the buttons. Does the glass block the camera from detecting the light?
Point the remote toward a mirror and look at the image through the camera while you press the buttons. Does the light from the remote bounce off the mirror into the camera?
Try to change channels on the television while pointing the remote control through a single layer of material from a black plastic trash bag. Did it work? Try the same thing through two or more layers, and then do the same experiment with the digital camera.
Is there an image in the digital camera when you push buttons on the plastic-covered remote?
The human eye is not sensitive to the infrared light used by television remote controls. Our eyes can only see a portion of the electromagnetic spectrum, and infrared light—which has lower frequency, longer wavelengths, and less energy per photon than red light—is just outside the range of the light we can see.
Infrared light is often divided into the near infrared, which is closest to the visible spectrum, and far infrared, which is emitted by warm objects. To send a signal to a television, remote controls often use a diode that emits light at around 940 nanometers in wavelength, which falls into the range of near-infrared light.
Some digital cameras have filters to block near-infrared light, but most can detect it. It shows up on the screen as if it were visible light. When you press a button on the remote control, the camera may show a pulsing light emitted by the remote. The pulses are coded to control the television.
Infrared light and visible light interact with materials in different ways. Near-infrared light passes through clear glass and will reflect off metal surfaces, including mirrors. Infrared light passes through most black plastic trash bags, so you should be able to control your television even with the remote covered in plastic.
Astronomers use infrared light to look through dust clouds because it passes through dust better than visible light, just as it passes through a black plastic trash bag.
Thermal cameras like the ones you see in science museums work in the far infrared. They show the infrared light emitted by warm objects. Far-infrared light is not detected by digital cameras and will not pass through clear plastic or water.