In this laboratory session, we will use a water droplet to turn a smartphone camera into a macro camera allowing us to take pictures of things that would normally be too close to focus on.
This page will give you some useful information about how the lab works, and what you will need to complete it. Once you are done reading, scroll to the bottom to enter the lab!
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(Optional) These can be used to change how the water droplet affects the image.
(Optional) If you want to take some pictures, the headphones can be used as a shutter button.
(Optional) A second phone or torch can be used to back-light your sample and improve the images.
If you are using the front camera of your phone you can use a clear plastic bottle to hold the water droplets. This should minimise spillage on to the phone, and makes it easier to change the size of the droplets:
Using the back camera of your phone will be a little more difficult, because you will need to keep the droplet from falling off, but it does give a more pronounced magnification effect because gravity helps to curve the surface of the droplet. Applying clingfilm helps the droplet to stick to your camera and protects your phone:
This experiment works because light rays move at different speeds in different substances.
Light rays slow down and change direction when they enter materials that have a higher density than air. The amount that a substance will bend light rays is called a substance’s refractive index. While this may sound technical, you’ve seen refraction at work many times. Have you ever noticed that your legs look strangely bent when you’re dangling them in a pool? This is because the light is being refracted when it hits the water.
When a light passes through a curved surface the light will bend by different amounts, which results in the light rays converging or diverging. This is how a magnifying glass works. Magnifying glasses are convex lenses, which cause light to refract and converge. This means that the object seen through the magnifying glass appears to be larger.
The lenses in a mobile phone are set to focus at a certain distance. Any object that is closer than the camera's minimum focus distance will be out of focus.
It's easy to test this, if you hold a leaf close to the phone, the phone will not be able to focus on it closer than 5 or 6cm. By adding a water droplet above the lens, we reduce the minimum focus distance.
The water droplet acts similarly to how a magnifying glass would work, bending the light rays and causing them to converge closer. This means that objects that are closer to the camera remain in focus.
