Can you reflect a wave completely

The normal is an imaginary line at right angles to the plane mirror. Smooth surfaces produce strong echoes when sound waves hit them, and they can act as mirrors when light waves hit them. The waves are reflected uniformly and light can form images. The waves can:. Rough surfaces scatter sound and light in all directions. But what if the original medium were attached to another rope with different properties?

How could the reflected pulse and transmitted pulse be described in situations in which an incident pulse reflects off and transmits into a second medium? Let's consider a thin rope attached to a thick rope, with each rope held at opposite ends by people. And suppose that a pulse is introduced by the person holding the end of the thin rope. If this is the case, there will be an incident pulse traveling in the less dense medium the thin rope towards the boundary with a more dense medium the thick rope.

The reflected pulse will be found to be inverted in situations such as this. During the interaction between the two media at the boundary, the first particle of the more dense medium overpowers the smaller mass of the last particle of the less dense medium.

This causes an upward displaced pulse to become a downward displaced pulse. The more dense medium on the other hand was at rest prior to the interaction. The first particle of this medium receives an upward pull when the incident pulse reaches the boundary. Since the more dense medium was originally at rest, an upward pull can do nothing but cause an upward displacement.

For this reason, the transmitted pulse is not inverted. In fact, transmitted pulses can never be inverted. Since the particles in this medium are originally at rest, any change in their state of motion would be in the same direction as the displacement of the particles of the incident pulse.

The Before and After snapshots of the two media are shown in the diagram below. Comparisons can also be made between the characteristics of the transmitted pulse and those of the reflected pulse. Once more there are several noteworthy characteristics.

One goal of physics is to use physical models and ideas to explain the observations made of the physical world. So how can these three characteristics be explained? First recall from Lesson 2 that the speed of a wave is dependent upon the properties of the medium. In this case, the transmitted and reflected pulses are traveling in two distinctly different media. Waves always travel fastest in the least dense medium. Thus, the reflected pulse will be traveling faster than the transmitted pulse.

Second, particles in the more dense medium will be vibrating with the same frequency as particles in the less dense medium. Since the transmitted pulse was introduced into the more dense medium by the vibrations of particles in the less dense medium, they must be vibrating at the same frequency.

So the reflected and transmitted pulses have the different speeds but the same frequency. Since the wavelength of a wave depends upon the frequency and the speed, the wave with the greatest speed must also have the greatest wavelength. Finally, the incident and the reflected pulse share the same medium.

Since the two pulses are in the same medium, they will have the same speed. Since the reflected pulse was created by the vibrations of the incident pulse, they will have the same frequency. And two waves with the same speed and the same frequency must also have the same wavelength. Finally, let's consider a thick rope attached to a thin rope, with the incident pulse originating in the thick rope. If this is the case, there will be an incident pulse traveling in the more dense medium thick rope towards the boundary with a less dense medium thin rope.

Once again there will be partial reflection and partial transmission at the boundary. The reflected pulse in this situation will not be inverted. Similarly, the transmitted pulse is not inverted as is always the case. Since the incident pulse is in a heavier medium, when it reaches the boundary, the first particle of the less dense medium does not have sufficient mass to overpower the last particle of the more dense medium. The result is that an upward displaced pulse incident towards the boundary will reflect as an upward displaced pulse.

For the same reasons, a downward displaced pulse incident towards the boundary will reflect as a downward displaced pulse. Comparisons between the characteristics of the transmitted pulse and the reflected pulse lead to the following observations. These three observations are explained using the same logic as used above. Once this pulse strikes the thicker string, some of it transmits, without any change in phase, while the remaining part reflects with a full phase change totally flipped.

When the incident pulse at the interface moves from the thick string, as shown by the lower two drawings with red arrows, neither the reflected nor the transmitted pulses change phase.

When light travels from a higher index material into a lower one, as, for example, from water to air, it bends outward from the perpendicular. Of course it also partially reflects off the interface. The larger the angle of incidence, the more it will bend out. But there is a limit to this, since the maximum angle that the beam can bend out in the lower index medium is 90 degrees.

If the incident angle gets larger, then the transmitted beam would not be able to bend out any further. This angle of incidence, for which the transmitted beam goes along the interface and does not enter the lower index side, is called the critical angle. When the incident angle gets any larger than the critical angle, then the beam will no longer transmit though the interface, but it will fully reflect!

This phenomena is called total internal reflection. Notice that all rays with larger angle of incidence than the red colored ray, such as the blue colored one, do not transmit into the lower index medium. This red colored ray's angle of incidence is the critical angle. Total internal reflection is the phenomena that allows wave guides to deliver waves from one point in space to another with little or no attenuation. In the visible region of electromagnetic spectrum a wave guide is called an optical fiber.

More on this later. Questions on Reflection and Refraction. As we have already studied, interference and diffraction are two wave properties that make waves very different from "non-wave" material objects. When two waves reach a point in space at the same time, they can produce a disturbance that is larger or smaller than the disturbance each one of them separately can produce. The strength of the "sum" disturbance depends on the relative phase of the two waves at that point in space.

If the two waves have equal wavelength, and if their relative phase does not change in time, then the value of the disturbance at the fixed point in space remains the same and does not change with time. Two waves that possess these features are said to be coherent. So, the interference of two waves that are coherent with each other results in a disturbance pattern that may vary from one point in space to the next, but for any fixed point it does not change with time; i. The simplest way of forming two waves that have the same wavelength and that produce phase differences that do not change with time is to reflect a wave from an interface that does not absorb any of the wave's energy.

Then the reflected wave will not only have the same wavelength, but it will also have the same amplitude. The resulting interference produces a disturbance that has twice the wave amplitude of the original wave at some points in space points of interference maxima to no disturbance or amplitude at all for other points in space points of interference minima and everything in between.

For a vibrating string, when the frequency of vibration is such that an integer multiple of half-wavelengths fit on the string, then a standing wave is established, as we now will see. In the above picture the string is made to vibrate with three separate frequencies, each resulting in a wavelength just right to set up a standing wave. Notice that there are many, many frequencies that cannot form a wavelength that results in a standing wave. Please recall that the speed of the wave depends on the material that the string is made of and the tension of the string.

Once we leave these parameters fixed, the speed is fixed. Then as the frequency increases, the wavelength decreases. So, each frequency of vibration leads to a corresponding wavelength value. Only very special values of the frequency result in wavelengths that produce a standing wave.

These special frequencies that result in standing waves are referred to as resonant frequencies. Standing waves on a string. The mechanical driver at the right is made to oscillate up and down at a resonant frequency of the string producing standing waves. Mapping of the "nodes," or stationary lines, on the surface of a "violin" made to oscillate at two different resonant frequencies.

In the case of light, of course the way to generate a reflection is by using mirrors. One instrument that uses a single source of light and generates standing waves is called a Michelson interferometer , after its American inventor.

This very cleverly designed and sensitive instrument uses a partially reflecting mirror, called a beam-splitter, to break a beam of light into two separate beams. These beams are each retro-reflected and combined to interfere at a screen. One of the two retro-reflecting mirrors is fixed, but the other can be moved to shorten or extend its distance from the beam-splitter.

By changing the position of this mirror, the interference on the screen can be varied from a totally constructive one when the beams form interference maxima to a totally destructive one. In changing from a maximum to a minimum in this way, the beam from the moving mirror has traveled an extra half of its wavelength, i.

On the top is a Michelson interferometer; in the middle is a schematic of its operation; below is the pattern observed on a screen when a He-Ne laser beam is used - as the movable mirror is scanned one-quarter of a wavelength the center varies from dark to light.

Another way to generate two coherent beams is to place two very small openings in front of a single beam. These openings are often in the form of very thin slits, so the interference that they produce is called "double-slit Interference". The interference pattern that the double-slit produces depends on the slit dimensions as well as on the wavelength of the light used. Specifically, to observe any interference effects at all we need slits that are comparable in size to the wavelength of the light.

In addition, we need light that is in phase at the two slits, i.