For a light ray traveling from air into water, for example, the critical angle is 48.5° If a ray of light’s angle of incidence is 50° (measured from the perpendicular), it will be completely reflected. Total internal reflection occurs when the angle of incidence is greater than the critical angle for a given transition between materials. You may have encountered this phenomenon when swimming underwater and looking up to see a “reflection” of the pool or ocean bottom. Geometrically, it is as if the light bends so much that the reflective angle is more than 90° from vertical. Total internal reflection occurs when light crosses from a material of high refractive index to a material of low refractive index. The component pointing parallel to the wall stays the same. After the reflection, the component pointing perpendicular to the wall reverses its direction. To understand this, decompose the initial vector of light into two components. When light is shone at an angle, the same concept is at work. After it hits the surface, it is reflected back in the same direction it came from. The simplest form of specular reflection occurs when light is shone perpendicularly at a surface. Specular reflection occurs when light reflects off a smooth surface at a definite angle. There are two types of reflection: specular reflection and diffuse reflection. Reflection occurs when light bounces off of a surface. Light interacts with solids and objects in different ways. c) Reflection, refraction, and Snell’s law The resulting diffraction pattern from a single slit appears to be more generally dispersed than the pattern resulting from a double slit. The waves of light passing through this slit are still able to constructively and destructively interfere with each other. Since there is only one slit, only one beam of light is allowed through. In contrast to the double-slit experiment, in the single-slit experiment, light is shone through a single slit. The bright spots are relatively narrow, while the dark spots are wider. The bright spots and dark spots from a diffraction grating are more intense, and the transition between them is more abrupt. Wave superposition occurs when two or more waves are travelling through the same medium at. What happens when we change the orientation of these two slits? A screen with many slits evenly spaced and placed close together is called a diffraction grating. Diffraction is the bending of waves around obstacles and openings. The other condition for interference is that the light must be monochromatic, meaning it consists of only one frequency or color. This is satisfied in the double-slit experiment because the light coming through each slit is generated by the same source and therefore must maintain the same phase relationship and amplitude. Note that for any interference to occur, the light sources must be coherent, meaning the waves are in-phase. While you won’t be expected to apply this equation on the MCAT, it’s useful to understand each variable. Take a moment to match the different terms in the equation to the image above it. Practicing with these questions will not only test your knowledge of light and optics but also show you how the AAMC likes to ask questions. At the end of this guide, you will also find an MCAT-style practice passage and standalone questions. Be sure to understand these terms and use them to create your own examples. However, understanding the fundamentals of this field will make understanding light and optics in relation to biology much smoother.īelow, the most important terms are in bold font. In all likelihood, when it does come up on the MCAT, it will be in a strictly biological context as opposed to the physics and mathematical contexts in the sections below. For this reason, it is considered to be a medium-yield topic on the MCAT. Light and optics are important for light-related reactions and many precision instruments you might find in a lab. When the aperture is larger than the wavelength most waves pass through and little diffraction occurs and when the aperture is much smaller than the wavelength most waves are blocked.In this guide on light and optics, we will study the characteristics of light: including its trajectory and propagation. The size of the aperture (or object) determines the extent of diffraction, with the most significant diffraction occurring when the aperture is of the same order of magnitude as the wavelength of the wave. Diffractionĭiffraction is the spreading out of a wave when it passes through an aperture (gap/hole) or around an object. IMPORTANT NOTE: If a wave enters a medium at 90º to the surface (parallel to the normal) it is not refracted.
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