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Suppose you put on two pairs of Polaroid sunglasses with their axes at an angle of 15.0o. How much longer will it take the light to deposit a given amount of energy in your eye compared with a single pair of sunglasses? Assume the lenses are clear except for their polarizing characteristics.

Plane polarizedlight

Polaroid sunglasses are familiar to most of us. They have a special ability to cut the glare of light reflected from water or glass as shown in the figure below. Polaroids have this ability because of a wave characteristic of light called polarization. What is polarization? How is it produced? What are some of its uses? The answers to these questions are related to the wave character of light.

Combination lasers project both lines and spots simultaneously or independently. These lasers are great for professionals who complete a wide range of projects as they allow the user to switch between lines, spots, or both depending on the job at hand. Electricians and plumbers will find these lasers to be extremely helpful for countless applications such as installing lighting, outlets, running wires, and pipes.

If a polarizing filter reduces the intensity of polarized light to 50.0 % of its original value, by how much are the electric and magnetic fields reduced?

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Light is one type of electromagnetic (EM) wave. As noted earlier, EM waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation (see Figure 2). There are specific directions for the oscillations of the electric and magnetic fields. Polarization is the attribute that a wave’s oscillations have a definite direction relative to the direction of propagation of the wave. (This is not the same type of polarization as that discussed for the separation of charges.) Waves having such a direction are said to be polarized. For an EM wave, we define the direction of polarization to be the direction parallel to the electric field. Thus we can think of the electric field arrows as showing the direction of polarization, as in Figure 2.

DEWALT offers spot lasers in both 3-spot and 5-spot. A 3-spot provides plumb and forward-facing dots whereas the 5-spot adds a right and left dot for transfer of points from wall to wall. A suggested SKU is our Green Beam 3 Spot Laser (DW083CG) with a high-visibility green beam. This laser includes a single lever power switch that locks the pendulum in the off position, as well as a built-in magnetic pivoting bracket to easily mount the laser onto metal surfaces.

From an accuracy standpoint, DEWALT offers a rotary laser that works up to 2,200 feet with an accuracy of 1/16 inch at 100 feet. This laser is the 20V MAX* Tool Connect™ Green Tough Rotary Laser (DW080LGS). This rotary laser is extremely durable with the ability to withstand up to a 6-foot drop, and an IP67 rating for water and dust protection. Connect it to the Tool Connect™ app via Bluetooth® technology for features including tool tracking, bump notifications, fall and drop indications, and changes in slope and line detection.

DEWALT offers combination lasers in both red and green variations. Our newest combination lasers are offered in the 12V MAX* system and include 2-spot cross and 5-spot cross models. A suggested SKU is our 12V MAX* 5 Spot + Cross Line Green Laser. This laser includes an integrated bracket to easily mount onto metal surfaces. It also offers a 165-foot range with a detector for the line, and a 150-foot range for the spot.

Polarisationmeaningin Physics

3: If you have completely polarized light of intensity 150 W/m2 what will its intensity be after passing through a polarizing filter with its axis at an 89.0o angle to the light’s polarization direction?

12: Light reflected at 55.6o from a window is completely polarized. What is the window’s index of refraction and the likely substance of which it is made?

Meaning of polarization of lightin physics

Let’s begin with the most common laser found on a jobsite, the line laser. A line laser projects an accurate horizontal or vertical illuminated line onto the surface at which the laser is pointed. Use line lasers indoors when installing cabinetry, tile, a drop ceiling, or for basic leveling. They can also be used outdoors when framing or installing a deck.

Many crystals and solutions rotate the plane of polarization of light passing through them. Such substances are said to be optically active. Examples include sugar water, insulin, and collagen (see Figure 13). In addition to depending on the type of substance, the amount and direction of rotation depends on a number of factors. Among these is the concentration of the substance, the distance the light travels through it, and the wavelength of light. Optical activity is due to the asymmetric shape of molecules in the substance, such as being helical. Measurements of the rotation of polarized light passing through substances can thus be used to measure concentrations, a standard technique for sugars. It can also give information on the shapes of molecules, such as proteins, and factors that affect their shapes, such as temperature and pH.

1: What angle is needed between the direction of polarized light and the axis of a polarizing filter to cut its intensity in half?

**With respect to 20V MAX* - Maximum initial battery voltage (measured without a workload) is 20 volts. Nominal voltage is 18.

Polarized and unpolarizedlight

where Io is the intensity of the polarized wave before passing through the filter. (The above equation is known as Malus’s law.)

2: The angle between the axes of two polarizing filters is 45.0 degrees. By how much does the second filter reduce the intensity of the light coming through the first?

4: Explain what happens to the energy carried by light that it is dimmed by passing it through two crossed polarizing filters.

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Light reflected at these angles could be completely blocked by a good polarizing filter held with its axis vertical. Brewster’s angle for water and air are similar to those for glass and air, so that sunglasses are equally effective for light reflected from either water or glass under similar circumstances. Light not reflected is refracted into these media. So at an incident angle equal to Brewster’s angle, the refracted light will be slightly polarized vertically. It will not be completely polarized vertically, because only a small fraction of the incident light is reflected, and so a significant amount of horizontally polarized light is refracted.

A fairly large angle between the direction of polarization and the filter axis is needed to reduce the intensity to 10.0% of its original value. This seems reasonable based on experimenting with polarizing films. It is interesting that, at an angle of 45o, the intensity is reduced to 50% of its original value (as you will show in this section’s Problems & Exercises). Note that 71.6o is 18.4o from reducing the intensity to zero, and that at an angle of 18.4o the intensity is reduced to 90.0% of its original value (as you will also show in Problems & Exercises), giving evidence of symmetry.

Figure 8 illustrates what happens when unpolarized light is reflected from a surface. Vertically polarized light is preferentially refracted at the surface, so that the reflected light is left more horizontally polarized. The reasons for this phenomenon are beyond the scope of this text, but a convenient mnemonic for remembering this is to imagine the polarization direction to be like an arrow. Vertical polarization would be like an arrow perpendicular to the surface and would be more likely to stick and not be reflected. Horizontal polarization is like an arrow bouncing on its side and would be more likely to be reflected. Sunglasses with vertical axes would then block more reflected light than unpolarized light from other sources.

Since the part of the light that is not reflected is refracted, the amount of polarization depends on the indices of refraction of the media involved. It can be shown that reflected light is completely polarized at a angle of reflection θb, given by

To examine this further, consider the transverse waves in the ropes shown in Figure 3. The oscillations in one rope are in a vertical plane and are said to be vertically polarized. Those in the other rope are in a horizontal plane and are horizontally polarized. If a vertical slit is placed on the first rope, the waves pass through. However, a vertical slit blocks the horizontally polarized waves. For EM waves, the direction of the electric field is analogous to the disturbances on the ropes.

(a) On a day when the intensity of sunlight is 1.00 kW/m2, a circular lens 0.200 m in diameter focuses light onto water in a black beaker. Two polarizing sheets of plastic are placed in front of the lens with their axes at an angle of 20.0o. Assuming the sunlight is unpolarized and the polarizers are 100% efficient, what is the initial rate of heating of the water in oC/s, assuming it is 80.0% absorbed? The aluminum beaker has a mass of 30.0 grams and contains 250 grams of water. (b) Do the polarizing filters get hot? Explain.

6: Show that if you have three polarizing filters, with the second at an angle of 45o to the first and the third at an angle of 90.0o to the first, the intensity of light passed by the first will be reduced to 25.0% of its value. (This is in contrast to having only the first and third, which reduces the intensity to zero, so that placing the second between them increases the intensity of the transmitted light.)

Polarizationdefinition in Chemistry

Spot lasers differ from line lasers in that they project a small circle of light onto the surface your laser is focused on. They are intended for transferring points from one surface to another. This could be for making sure a joist or wall is plumb (vertical) or to ensure pipes traveling from floor to floor are plumb. Spot lasers are most commonly used for plumbing installation, electrical work, HVAC, and framing applications.

Line lasers are offered with a red beam or a green beam. A green beam is easier to see with the human eye because the green wavelength is larger than red. Green is also more visible in sunlight, so it is easier to see outside. When it comes to the visibility range, it depends on the lighting conditions. In dim, dusk-like conditions, it is possible to see a green beam for over 100 feet. One thing to keep in mind is that green beams do require more battery power than red beam lasers.

where n1 is the medium in which the incident and reflected light travel and n2 is the index of refraction of the medium that forms the interface that reflects the light. This equation is known as Brewster’s law, and θb is known as Brewster’s angle, named after the 19th-century Scottish physicist who discovered them.

There is a range of optical effects used in sunglasses. Besides being Polaroid, other sunglasses have coloured pigments embedded in them, while others use non-reflective or even reflective coatings. A recent development is photochromic lenses, which darken in the sunlight and become clear indoors. Photochromic lenses are embedded with organic microcrystalline molecules that change their properties when exposed to UV in sunlight, but become clear in artificial lighting with no UV.

Rotary lasers are used to kick off nearly every professional construction job. Their applications range from grade work (digging foundations), to layout and masonry. Both dual-slope and single-slope rotary lasers are used to continue a desired pitch across a large area. The desired pitch might be level for finding grade or when using a reference line. Dual-slope means that the line will move along both the X axis and Y axis. X mode is used often to “walk” the line in vertical mode for aligning metal track. Y is used to angle the line in horizontal mode for setting slope or setting pitch on a driveway.

Grade rods are used in conjunction with rotary lasers for digging or leveling earth. You must move the detector up or down on the grade rod while the rotary is spinning until you identify the laser line. When that laser line is found you have then established “grade” or level. If you are looking to dig a hole that is 3 inches deep, for example, you would move the detector 3 inches up the grade rod. After you dig 3 inches down and place the grade rod in the hole, you should hear a beep and read that the laser is hitting the detector. This is verification that you have dug the 3 inches deep.

By now you can probably guess that Polaroid sunglasses cut the glare in reflected light because that light is polarized. You can check this for yourself by holding Polaroid sunglasses in front of you and rotating them while looking at light reflected from water or glass. As you rotate the sunglasses, you will notice the light gets bright and dim, but not completely black. This implies the reflected light is partially polarized and cannot be completely blocked by a polarizing filter.

*With respect to 12V MAX* - Maximum initial battery voltage (measured without a workload) is 12 volts. Nominal voltage is 10.8.

(a) At what angle will light traveling in air be completely polarized horizontally when reflected from water? (b) From glass?

Polarizing filters have a polarization axis that acts as a slit. This slit passes electromagnetic waves (often visible light) that have an electric field parallel to the axis. This is accomplished with long molecules aligned perpendicular to the axis as shown in Figure 9.

What ispolarization ofwaves in Physics

As you can see, DEWALT offers a robust line of lasers including spot, line, combination, and rotary, as well as laser accessories to go with them. With the professional in mind, we will continue to evolve and innovate these products to accommodate needs on the jobsite. Keep checking back to see what new products DEWALT has to offer.

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Choosing the right laser can be hard. With such a wide offering, how do you know which one to choose for your job? In this article, we’ll dive into each type of laser and for which applications each is most commonly used. We’ll also outline a few key products offered by DEWALT for each category.

3: No light passes through two perfect polarizing filters with perpendicular axes. However, if a third polarizing filter is placed between the original two, some light can pass. Why is this? Under what circumstances does most of the light pass?

When the intensity is reduced by 90.0% it is 10% or 0.100 times its original value. That is, I = 0.100 I0. Using this information, the equation I = I0 cos2θ can be used to solve for the needed angle.

Glass and plastic become optically active when stressed; the greater the stress, the greater the effect. Optical stress analysis on complicated shapes can be performed by making plastic models of them and observing them through crossed filters, as seen in Figure 14. It is apparent that the effect depends on wavelength as well as stress. The wavelength dependence is sometimes also used for artistic purposes.

17: (a) 2.07 x10-2 o C/s (b) Yes, the polarizing filters get hot because they absorb some of the lost energy from the sunlight.

Polarization of lightnotes PDF

5: At the end of Example 1, it was stated that the intensity of polarized light is reduced to 90.0% of its original value by passing through a polarizing filter with its axis at an angle of 18.4 degrees to the direction of polarization. Verify this statement.

Polarizationby reflection

What angle is needed between the direction of polarized light and the axis of a polarizing filter to reduce its intensity by 90.0 %?

14: If θb is Brewster’s angle for light reflected from the top of an interface between two substances, and θb‘ is Brewster’s angle for light reflected from below, prove that θb + θb‘ = 90o..

The Sun and many other light sources produce waves that are randomly polarized (see Figure 4). Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization. Polaroid materials, invented by the founder of Polaroid Corporation, Edwin Land, act as a polarizing slit for light, allowing only polarization in one direction to pass through. Polarizing filters are composed of long molecules aligned in one direction. Thinking of the molecules as many slits, analogous to those for the oscillating ropes, we can understand why only light with a specific polarization can get through. The axis of a polarizing filter is the direction along which the filter passes the electric field of an EM wave (see Figure 5).

We'll dive into each type of laser and for which applications each is most commonly used. We'll also outline a few key products offered by DEWALT for each category.

If you hold your Polaroid sunglasses in front of you and rotate them while looking at blue sky, you will see the sky get bright and dim. This is a clear indication that light scattered by air is partially polarized. Figure 11 helps illustrate how this happens. Since light is a transverse EM wave, it vibrates the electrons of air molecules perpendicular to the direction it is traveling. The electrons then radiate like small antennae. Since they are oscillating perpendicular to the direction of the light ray, they produce EM radiation that is polarized perpendicular to the direction of the ray. When viewing the light along a line perpendicular to the original ray, as in Figure 11, there can be no polarization in the scattered light parallel to the original ray, because that would require the original ray to be a longitudinal wave. Along other directions, a component of the other polarization can be projected along the line of sight, and the scattered light will only be partially polarized. Furthermore, multiple scattering can bring light to your eyes from other directions and can contain different polarizations.

All we need to solve these problems are the indices of refraction. Air has n1 = 1.00, water has n2 = 1.333, and crown glass has n’2 = 1.520. The equation can be directly applied to find θb in each case.

Photographs of the sky can be darkened by polarizing filters, a trick used by many photographers to make clouds brighter by contrast. Scattering from other particles, such as smoke or dust, can also polarize light. Detecting polarization in scattered EM waves can be a useful analytical tool in determining the scattering source.

While you are undoubtedly aware of liquid crystal displays (LCDs) found in watches, calculators, computer screens, cellphones, flat screen televisions, and other myriad places, you may not be aware that they are based on polarization. Liquid crystals are so named because their molecules can be aligned even though they are in a liquid. Liquid crystals have the property that they can rotate the polarization of light passing through them by 90o. Furthermore, this property can be turned off by the application of a voltage, as illustrated in Figure 12. It is possible to manipulate this characteristic quickly and in small well-defined regions to create the contrast patterns we see in so many LCD devices.

DEWALT offers these lasers on a 12V MAX* battery platform as well as with Alkaline batteries. Plus, our line lasers offer an integrated magnetic bracket to make them easy to mount during use. Suggested SKUs include our 12V MAX* 3 X 360 Green Line Laser (DW089LG) and our Green Cross Line Laser (DW088CG).

13: (a) Light reflected at 62.5o from a gemstone in a ring is completely polarized. Can the gem be a diamond? (b) At what angle would the light be completely polarized if the gem was in water?

There are two types of projections, a forward projection and a 360 projection. The forward projection does just what it sounds like, it projects a line directly onto the surface where the laser is pointed. Similarly, the 360 projection will project a line 360 degrees surrounding the laser. For example, when using a line laser in a room, the forward projection would provide you with a line on one wall whereas the 360 would project that line on all four walls of the room.

7: When light is reflected at Brewster’s angle from a smooth surface, it is 100% polarized parallel to the surface. Part of the light will be refracted into the surface. Describe how you would do an experiment to determine the polarization of the refracted light. What direction would you expect the polarization to have and would you expect it to be 100 %?

Only the component of the EM wave parallel to the axis of a filter is passed. Let us call the angle between the direction of polarization and the axis of a filter θ. If the electric field has an amplitude E, then the transmitted part of the wave has an amplitude Ecosθ (see Figure 7). Since the intensity of a wave is proportional to its amplitude squared, the intensity I of the transmitted wave is related to the incident wave by

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5: When particles scattering light are much smaller than its wavelength, the amount of scattering is proportional to 1/ λ4. Does this mean there is more scattering for small λ than large λ? How does this relate to the fact that the sky is blue? Hint: red light has a wavelength of about 650 nm while blue light has a wavelength of about 400 nm.

Another interesting phenomenon associated with polarized light is the ability of some crystals to split an unpolarized beam of light into two. Such crystals are said to be birefringent (see Figure 15). Each of the separated rays has a specific polarization. One behaves normally and is called the ordinary ray, whereas the other does not obey Snell’s law and is called the extraordinary ray. Birefringent crystals can be used to produce polarized beams from unpolarized light. Some birefringent materials preferentially absorb one of the polarizations. These materials are called dichroic and can produce polarization by this preferential absorption. This is fundamentally how polarizing filters and other polarizers work. The interested reader is invited to further pursue the numerous properties of materials related to polarization.

There are 2 types of detectors used in the construction industry: Line and Rotary. Since line lasers and rotary lasers work on different wavelengths, they require specific detectors. The detectors are also color-specific. This means a red line laser requires a red line detector. For both rotary lasers and line lasers, detectors are not a requirement, but they do come in handy when the beam is no longer visible. For DEWALT, the standard visibility range on our line laser levels is 50 to 100 feet. While using the detector that range is extended out to 165 feet. Rotary laser detectors allow for detection up to 2,200 feet with the DW079 and DW080 series.

Find Polaroid sunglasses and rotate one while holding the other still and look at different surfaces and objects. Explain your observations. What is the difference in angle from when you see a maximum intensity to when you see a minimum intensity? Find a reflective glass surface and do the same. At what angle does the glass need to be oriented to give minimum glare?

Figure 10 illustrates how the component of the electric field parallel to the long molecules is absorbed. An electromagnetic wave is composed of oscillating electric and magnetic fields. The electric field is strong compared with the magnetic field and is more effective in exerting force on charges in the molecules. The most affected charged particles are the electrons in the molecules, since electron masses are small. If the electron is forced to oscillate, it can absorb energy from the EM wave. This reduces the fields in the wave and, hence, reduces its intensity. In long molecules, electrons can more easily oscillate parallel to the molecule than in the perpendicular direction. The electrons are bound to the molecule and are more restricted in their movement perpendicular to the molecule. Thus, the electrons can absorb EM waves that have a component of their electric field parallel to the molecule. The electrons are much less responsive to electric fields perpendicular to the molecule and will allow those fields to pass. Thus the axis of the polarizing filter is perpendicular to the length of the molecule.

In flat screen LCD televisions, there is a large light at the back of the TV. The light travels to the front screen through millions of tiny units called pixels (picture elements). One of these is shown in Figure 12 (a) and (b). Each unit has three cells, with red, blue, or green filters, each controlled independently. When the voltage across a liquid crystal is switched off, the liquid crystal passes the light through the particular filter. One can vary the picture contrast by varying the strength of the voltage applied to the liquid crystal.

Figure 6 shows the effect of two polarizing filters on originally unpolarized light. The first filter polarizes the light along its axis. When the axes of the first and second filters are aligned (parallel), then all of the polarized light passed by the first filter is also passed by the second. If the second polarizing filter is rotated, only the component of the light parallel to the second filter’s axis is passed. When the axes are perpendicular, no light is passed by the second.

4: What angle would the axis of a polarizing filter need to make with the direction of polarized light of intensity 1.00 kW/m2 to reduce the intensity to 10.0W/m2?