When do waves reflect

The normal is an imaginary line at right angles to the plane mirror. Make sure that you can label the normal, angle of incidence and angle of reflection on a diagram of reflection. Waves change speed when they pass across the boundary between two different substances, such as light waves refracting when they pass from air to glass.

This causes them to change direction and this effect is called refraction. Water waves refract when they travel from deep water to shallow water or vice versa. Refraction happens because the speed of the wave changes. The wavelength is equal to linear distance between repetitions of transverse disturbance or phase. Clearly, the displacement in y-direction is described by the bounded sine or cosine function. The important point here is to realize that oscillatory attributes like time period, angular and linear frequency of wave motion is same as that of vibration of a particle in transverse direction.

We know that time period in SHM is equal to time taken by the particle to complete one oscillation. Thus, speed of wave is given by:. Refraction is a surface phenomenon that occurs as the change in direction of a wave due to a change in its medium. Refraction is the change in direction of a wave due to a change in its medium. Essentially, it is a surface phenomenon—mainly in governance to the law of conservation of energy and momentum.

Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium e. In optics, refraction is a phenomenon that often occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle.

For example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index. A ray traveling along the normal perpendicular to the boundary will change speed, but not direction.

Refraction still occurs in this case. Understanding of refraction led to the invention of lenses and the refracting telescope. Refraction can be seen when looking into a bowl of water, as illustrated in. Air has a refractive index of about 1. This is due to the bending of light rays as they move from the water to the air. Once the rays reach the eye, the eye traces them back as straight lines lines of sight.

The lines of sight shown as dashed lines intersect at a higher position than where the actual rays originated causing the pencil to appear higher and the water to appear shallower than they actually are. Refraction in Water : An object in this case a pencil partially immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.

More accurately, for any angle of view, Y should be vertically above X, and the pencil should appear shorter, not longer as shown. Diffraction refers to various phenomena such as the bending of waves around obstacles and the spreading out of waves past small openings.

Diffraction refers to various phenomena which occur when a wave encounters an obstacle. In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.

Similar effects occur when a light wave travels through a medium with a varying refractive index, or a sound wave travels through one with varying acoustic impedance.

Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays and radio waves. As physical objects have wave-like properties at the atomic level , diffraction also occurs with matter and can be studied according to the principles of quantum mechanics. Diffraction effects are generally most pronounced for waves whose wavelengths are roughly similar to the dimensions of the diffracting objects.

If the obstructing object provides multiple, closely-spaced openings, a complex pattern of varying intensity can result. This is due to the superposition, or interference, of different parts of a wave that travel to the observer by different paths. A good example would be diffraction gratings. Intensity Pattern : Intensity pattern formed on a screen by diffraction from a square aperture.

The effects of diffraction are often seen in everyday life. The most striking examples of diffraction are those involving light. For example, the closely spaced tracks on a CD or DVD act as a diffraction grating to form the familiar rainbow pattern seen when looking at a disk. This principle can be extended to engineer a grating with a structure such that it will produce any diffraction pattern desired, like the hologram on a credit card.

Diffraction in the atmosphere by small particles can cause a bright ring to be visible around a bright light source like the sun or the moon. A shadow of a solid object, using light from a compact source, shows small fringes near its edges. The speckle pattern which is observed when laser light falls on an optically rough surface is also a diffraction phenomenon. All these effects are a consequence of the fact that light propagates as a wave.

In this atom, we will obtain a general mathematical form of a traveling wave. In the middle, we used the equation 1 along with the fact that partial derivatives are interchangeable.

From the chain rules,. Therefore, we see that. Converting back to the original variables of x and t, we conclude that the solution of the original wave equation is. In other words, solutions of the 1D wave equation are sums of a left traveling function f and a right traveling function g. The wave function is further determined by taking additional information, usually given as boundary conditions and some others.

Also, the shape of the function at an instance can be provided to determine the function. Wave Equation in Two Dimensions : A solution of the wave equation in two dimensions with a zero-displacement boundary condition along the entire outer edge. Diffraction can be demonstrated by placing small barriers and obstacles in a ripple tank and observing the path of the water waves as they encounter the obstacles.

The waves are seen to pass around the barrier into the regions behind it; subsequently the water behind the barrier is disturbed. The amount of diffraction the sharpness of the bending increases with increasing wavelength and decreases with decreasing wavelength. In fact, when the wavelength of the waves is smaller than the obstacle, no noticeable diffraction occurs.

Diffraction of water waves is observed in a harbor as waves bend around small boats and are found to disturb the water behind them. The same waves however are unable to diffract around larger boats since their wavelength is smaller than the boat.

Diffraction of sound waves is commonly observed; we notice sound diffracting around corners, allowing us to hear others who are speaking to us from adjacent rooms. Many forest-dwelling birds take advantage of the diffractive ability of long-wavelength sound waves. Owls for instance are able to communicate across long distances due to the fact that their long-wavelength hoots are able to diffract around forest trees and carry farther than the short-wavelength tweets of songbirds.

Diffraction is observed of light waves but only when the waves encounter obstacles with extremely small wavelengths such as particles suspended in our atmosphere. Diffraction of sound waves and of light waves will be discussed in a later unit of The Physics Classroom Tutorial. Reflection, refraction and diffraction are all boundary behaviors of waves associated with the bending of the path of a wave. The bending of the path is an observable behavior when the medium is a two- or three-dimensional medium.

Reflection occurs when there is a bouncing off of a barrier. Reflection of waves off straight barriers follows the law of reflection. Reflection of waves off parabolic barriers results in the convergence of the waves at a focal point. Refraction is the change in direction of waves that occurs when waves travel from one medium to another. Refraction is always accompanied by a wavelength and speed change.

Diffraction is the bending of waves around obstacles and openings. The amount of diffraction increases with increasing wavelength. Typical values for the index of refraction of glass are between 1. The distance between wave fronts will therefore be shorter in the glass than in air, since the waves travel a smaller distance per period T. Now consider wave fronts and their corresponding light rays approaching the surface at an angle. We can see that the rays will bend as the wave passes from air to glass.

The bending occurs because the wave fronts do not travel as far in one cycle in the glass as they do in air.

As the diagram shows, the wave front halfway into the glass travels a smaller distance in glass than it does in air, causing it to bend in the middle. Thus, the ray, which is perpendicular to the wave front, also bends. The situation is like a marching band marching onto a muddy field at an angle to the edge of the field.

The rows bend as the speed of the marchers is reduced by the mud. The amount of bending depends on the angle of incidence and on the indices of refraction of glass and air, which determine the change in speed.