Gravity bends light. One can argue this by reasoning that a beam of light should travel in a curved path when viewed from within an accelerating frame of reference, and then invoking Einstein's principle of equivalence, which asserts that the effects observed in an accelerating frame of reference are indistinguishable from the effects observed in…

Nearly everyone, including physics students, finds rainbows to be fascinating and much has been written about them. For example, in a 2020 paper, Kenneth Ford sets forth the basic theory of rainbows created by water droplets at the level of geometric optics and uses a graphical approach to address the question of the relative intensities of the…

In introductory texts, some "special" rays are selected to draw the image produced by lenses and mirrors. After teaching special rays, students usually ask how to draw an arbitrary ray. One method for drawing an arbitrary ray is the "tilted principal axis." As an example, the tracing of an arbitrary ray in diverging lens is…

This experiment demonstrates that copper(II) chloride dihydrate (CuCl[subscript 2]·2H[subscript 2]O) in different solvents (acetone, isopropyl alcohol, or water) displays divergent colors and visible-near IR spectra. Both the reactions of these solutions with 2 equiv of sodium hydroxide (NaOH) and the direct solid-state reaction of CuCl[subscript…

The refractive index is a number that governs how light changes its direction of propagation as it enters one material medium from another. This phenomenon is known as refraction and the angles of incidence and refraction of light, referred to the normal to the interface of the two media at the point of incidence, are related by Snell's law. The…

The interference pattern between two harmonic oscillations with slightly different frequencies are called beats. The beats, as a combined motion, have two different periods, one approximately equal to the period of the original oscillations, and another that is significantly longer and is related to the variable amplitude of the motion. The main…

Student misconceptions of the double-slit experiment (Fig. 1) are abundant. The most common ones that we observe include: (1) belief that constructive interference requires both pathlengths to be integer multiples of the wavelength ("L[subscript 1] = n[subscript 1][lambda]" and "L[subscript 2] = n[subscript 2][lambda]") rather…

The falling temperature of the photosphere with height is responsible for the effect known as limb darkening. The Sun is not equally bright all over the disc. When we observe the Sun towards the limbs, it appears to get darker. Light from the photosphere travels through an absorptive medium. Therefore, one can see only so far into the photosphere.…

Although it originates from the ancient Greeks, optics still arouses a lot of scientific interest, mainly due to the technological innovation associated with it. One of its most interesting applications is related to optical metrology and the characterization of materials through optical techniques. While some of these processes can be explained…

Sometimes it takes little to keep this physicist happy on an airplane. A window seat, where the plane's shadow is visible or has disappeared into the distance, provides the opportunity to observe a variety of phenomena associated with sunlight that is reflected, refracted or scattered back towards the Sun. The term "backscattering" is…

Two misconceptions about the mechanism of image formation in the human eye are common among students and even in textbooks and other teaching materials. The first attributes all refraction to the eye lens; the second treats the eye as a pinhole camera. To reduce these persistent conceptions of students, a series of simple experiments is presented…

The laser pointer has been widely used to demonstrate some simple optics phenomena, like reflection, refraction, total reflection, and diffraction. However, the rays of laser light cannot be seen in the air because the scattered light is too weak. Many physics teachers use milk or smoke to visualize rays of laser light in physics labs, but it is…

This paper proposes a simple method to design experiments for drawing the light paths at a lens to find its effective focal length and principal planes. In the designed experiments, long-exposure photography was used to record the light scattered using a moving sheet of paper, thus revealing the light path. According to the proposed experimental…

White light refracted by a glass edge or a prism might be split into the colors of the rainbow but, when restricted by a suitable arrangement of edges, might also yield a sequence of colors complementary to the rainbow. We studied the creation of these color fields experimentally with a setup consisting of RGB light-emitting diodes that cover all…

Solar limb darkening is a prominent feature seen in white images of the Sun: the brightness of the solar disk is greatest at the solar center and decreases radially outward towards the limb. White light images can be used to examine and even model limb darkening; however, the limb-darkening effect is, in fact, wavelength dependent. Limb darkening…