Nearly all natural surfaces other than liquid produce diffuse reflections. The interpretation that it was liquid, rather than very smooth sands for example, was confirmed when specular reflection of sunlight was imaged by cameras on the Cassini spacecraft. Radar and other sensors had discovered large areas that looked smooth and could be liquid methane. Scientists studying Saturn’s satellite Titan have used specular reflection to prove that liquids exist on that moon. The reason we see most objects is because light strikes and reflects off their rough surfaces in several directions.
This type of reflection is called diffuse reflection. Tiny irregularities in surfaces of paper and other objects will reflect light in many directions. The Law of Reflection works for smooth surfaces, but irregular surfaces are another story. The reflection off smooth surfaces is called specular reflection – light bounces off the surface like it does off mirrors (which used to be called specula, singular speculum). Rollover the blue area to see the degrees of reflection.This is the easiest equation in physics! If light strikes a surface at an angle of 30° from the vertical or normal, it bounces off at 30°. The angle of incident, i = the angle of reflection, r i = r
This Law of Reflection can be written as: The incoming angle is called the angle of incidence, and the angle of the outgoing ray is the angle of reflection. A beam of light striking a smooth flat surface such as a mirror is strongly reflected off the mirror, with the angle that the light ray bounces off the surface being identical to the angle it hit. We think of light as rays, thin beams of light that travel in straight lines. For this situation, all wavelengths of light are equally scattered in all directions.If you see something, it is reflecting light. This means that a lot of the blue light has been scattered out well before the light arrives at us, so the sky appears redder.Ĭlouds appear white because the water droplets are much larger than the wavelengths of light. This is similar to the question: “Why are sunsets red?” When the Sun appears lower in the sky, the light that reaches us has already travelled through a lot more of the atmosphere. When we look at the sky, we see all the places that the blue light has been scattered from. Blue light has a smaller wavelength than red light, so it is scattered much more than red light. As this light hits the particles of nitrogen and oxygen in our atmosphere, it is scattered in all directions. Light from the sun is made of all the colours of the rainbow. “Why is the sky blue?” is a common question. The amount of scattering depends on how big the particle is compared to the wavelength of light that is hitting it. Some light is scattered in all directions when it hits very small particles such as gas molecules or much larger particles such as dust or droplets of water. If imaginary lines are traced back, they appear to come from a focal point behind the mirror.Ĭonvex mirrors are useful for shop security and rear-view mirrors on vehicles because they give a wider field of vision. Parallel rays of light strike the mirror and are reflected outwards. The inside curve of a spoon is an example of a concave mirror It is possible to make mirrors that behave like humps or troughs, and because of the different way they reflect light, they can be very useful. This is because the reflecting surface is no longer flat and may have humps and troughs caused by the wind. However, if there are ripples or waves in the water, the reflection becomes distorted. When the water in a lake or sea is very still, the reflection of the landscape is perfect, because the reflecting surface is very flat. With a flat mirror, it is easy to show that the angle of reflection is the same as the angle of incidence. If you measure the angle of incidence and the angle of reflection against the normal, the angle of incidence is exactly the same as the angle of reflection. If you want to measure these angles, imagine a perfectly straight line at a right angle to the reflective surface (this imaginary line is called ‘normal’).