Why do pencils appear to bend in water

Share your ideas with us! Put the pencil in the water. Look at it from the top. Look at it from the side. Bending a Pencil Science Explained Light refraction occurs when something gets in the way of the light waves.

More fun science for kids:. Search for:. Many birds hunt by flying over the surface of water, then diving in once they see a fish. The bird has to adjust where it dives in order to catch the fish.

This effect is also caused by the refraction of light once it hits the water. Draw an arrow on a piece of paper and hold it up behind the glass of water, about 30 cm from your eyes. What do you observe? The round outside of the glass forces the water into a rounded shape, which acts as a convex lens.

This lens bends the incoming light towards the middle. Here, the light rays meet at what is called the focal point. Because the glass is so thin and because the light starts and finished in air, the refraction into and out of the glass causes little deviation in the light's original direction.

As you sight at the portion of the pencil that was submerged in the water, light travels from water to air or from water to glass to air. This light ray changes medium and subsequently undergoes refraction. As a result, the image of the pencil appears to be broken. Furthermore, the portion of the pencil that is submerged in water appears to be wider than the portion of the pencil that is not submerged.

These visual distortions are explained by the refraction of light. In this case, the light rays that undergo a deviation from their original path are those that travel from the submerged portion of the pencil, through the water, across the boundary, into the air, and ultimately to the eye.

At the boundary, this ray refracts. The eye-brain interaction cannot account for the refraction of light. As was emphasized in Unit 13, the brain judges the image location to be the location where light rays appear to originate from. This image location is the location where either reflected or refracted rays intersect. The eye and brain assume that light travels in a straight line and then extends all incoming rays of light backwards until they intersect. Light rays from the submerged portion of the pencil will intersect in a different location than light rays from the portion of the pencil that extends above the surface of the water.

For this reason, the submerged portion of the pencil appears to be in a different location than the portion of the pencil that extends above the water.

The diagram at the right shows a God's-eye view of the light path from the submerged portion of the pencil to each of your two eyes. Only the left and right extremities edges of the pencil are considered. The blue lines depict the path of light to your right eye and the red lines depict the path of light to your left eye. Observe that the light path has bent at the boundary. Dashed lines represent the extensions of the lines of sight backwards into the water. Observe that these extension lines intersect at a given point; the point represents the image of the left and the right edge of the pencil.