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Intensity

Measurements of light refer to the intensity. These measurements are obtained by dividing either a power or a luminous flux by a solid angle, a planar area or a combination of the two. Intensity is the power transferred per unit area. When intensity is measuring waves the average power transfer over one period of the wave is used.

Intensity is found by taking the energy density at an arbitrary point in space and multiplying it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area. In the SI system, the unit is watts per meter squared.

For a point source of radiating energy in three dimensions where there is no energy lost to the medium, the intensity decreases in proportion to the distance from the object squared. Applying the law of conservation of energy we obtain the following equation

P = ∫I * dA

Where

P is the net power radiated

I is the intensity as a function of position

In photometry and radiometry, intensity has different meanings. It is the luminous or radiant power per unit solid angle. This can cause confusion in optics where intensity can mean any of radiant intensity, luminous intensity or irradiant. This depends on the background of the person using the term. 

Categories within Intensity

Inverse Square Law

Postings: 6

The inverse-square law is any physical law stating that a specified physical quantity is inversely proportional to the square of the distance from the source.

A Hypothetical X-ray

** Please see the attached file for the complete solution ** See the attached file for a question about a hypothetical x-ray burst from an x-ray tube, and answer questions regarding the total number of x-ray photons, x-ray intensity, and the optical density profile.

X-ray Intensity

In figure 1.40 (see attachment), calculate the X-ray intensity, as a function of the incident intensity I_o, that reaches the film for each of the three X-ray beams. The dark-shaded area represents bone and the light-shaded area represents tissue. The linear attenuation coefficients at the effective X-ray energy of 68 KeV are

Relative intensities

In Figure 1.41, calculate the relative intensities of the signals S1, S2, and S3 produced by each crystal. The value of u_tissue is 0.5 cm^-1, u_bone is 1cm^-1, and u_crystal is 2cm^-1. ** Please the attached file for the complete problem description **

Environmental Factors in Everyday Life

As this chapter deals with "environmental factors," you can apply this material to your everyday life. Spend some time in thought, and identify a situation in your life, which is affected by noise, vibration, illumination, climate, and chemical substances. Your choice must include all of these conditions. Work through Checkli

Write a summary of the issues presented in this article. The case is attached Wireless Radiation Frying Your Brains? Radio waves, microwaves, and infrared all belong to the Electromagnetic radiation spectrum. These terms reference ranges of radiation frequencies we use every day in our wireless networking environments. However, the very word radiation strikes fear in many people. Cell towers have sprouted from fields all along highways. Tall rooftops harbor many more cell stations in cities. Millions of cell phone users place microwave transmitters/receivers next to their heads each time they make a call. Computer network wireless access points have become ubiquitous. Even McDonald's customers can use their machines to browse the Internet as they eat burgers. With all this radiation zapping about, should we be concerned? The electromagnetic spectrum ranges from ultra-low frequencies to radio waves, microwaves, infrared, visible light, ultraviolet, x-ray, and up to gamma ray radiation. Is radiation dangerous? The threat appears to come from two different directions, the frequency and the intensity. A preponderance of research has demonstrated the dangers of radiation at frequencies just higher than those of visible light, even including the ultraviolet light used in tanning beds, x-rays, and gamma rays. These frequencies are high (the wavelengths are small enough) to penetrate and disrupt molecules and even atoms. The results range from burns to damaged DNA that might lead to cancer or birth defects. However, radiation's lower frequencies ranging from visible light (the rainbow colors you can see), infrared, microwave, and radio waves have long waves unable to penetrate molecules. Indeed, microwave wave lengths are so long that microwave ovens employ a simple viewing screen that can block these long waves and yet allow visible light through. As a result, we can watch our popcorn pop without feeling any heat. Keep in mind that visible light consists of radiation frequencies closer to the danger end of the spectrum than microwave light. Lower radiation frequencies can cause damage only if the intensity is strong enough, and that damage is limited to common burns. Microwave ovens cook food by drawing 800 or more watts and converting them into a very intense (bright) microwave light. Cellular telephones, by comparison, draw a very tiny amount of current from the phone's battery and use the resulting microwaves to transmit a signal. In fact, the heat you feel from the cell phone is not from the microwaves but rather from its discharging battery. It is extremely unlikely that either device can give the user cancer, though a microwave oven could cause serious burns if the operator disables its safety features.

Write a summary of the issues presented in this article. The case is attached Wireless Radiation Frying Your Brains? Radio waves, microwaves, and infrared all belong to the Electromagnetic radiation spectrum. These terms reference ranges of radiation frequencies we use every day in our wireless networking environments. How

Light Attenuation Under Water

When the light penetrates through the water in a lake, the light intensity decreases with depth. Light intensity f (x) is given by f (x) = 100*(a)^x Where x is the depth measured in meters below the lake's surface. For a certain pure and kalr lake, the light intensity 16 of 5.0 meters. a) Determine the number a b) Deter

Light: Variation in Intensity and Axis of Polarization

4. Light is reflected off the rear windshield of a car. When the Polaroid is rotated so that the 0 degree or 360 degree mark is at the top, the transmitted intensity is minimum, while at 90 degrees and 27- degrees it is maximum. Explain why this variation in intensity occurs. 5. What is the direction for the axis of pola

Polarization of Light: Intensity Variation

3. You view light from a flashpoint through a Polaroid. Describe any intensity variation as the Polaroid is rotated. Explain your answer. Describe any intensity variation as the flashlight is rotated. 4. Unpolarized light travels through two pieces of Polaroid as shown below. When the two Polaroids are rotated to 0 d

Determining the Intensity of a Light Bulb: Example Question

Intensity of a Light Bulb The farther a person is from a light bulb, the less intense its light is. The equation I = 19 / 4d^2 approximates the intensity of light from a 60-watt light bulb at a distance of d meters, where I is measured in watts per square meter. (a) Find I for D = 2 meters and interpret the result. (b) T

Physics: Beam of vertically polarized light impinges on two polarizers

See attached file. Please answer the following true and false questions and provide explanations for each. A beam of vertically polarized light impinges on two polarizers, in each of three different cases. Which of the following statements are true about these cases? 1. (T/F) transmitted intensity is lowest in both Cases

Interference of light: Double slit experiment.

When green light passes through a double slit arrangement in air, the interference pattern in Figure (a) above is observed on a distant screen. It is possible to alter the interference pattern to look like Figure (b) by changing specific parameters. Which of the following changes would result in obtaining the pattern shown in Fi

Intensity transmitted by the other polarizing eye of the spider

Experiments show that the ground spider Drassodes cupreus uses one of its several pairs of eyes as a polarization detector. In fact, the two eyes in this pair have polarization directions that are at right angles to one another. Suppose linearly polarized light with an intensity of 844 W/m2 shines from the sky onto the spider, a

Uses one pair of eyes as a polarization detector

Part 1 Experiments show that the ground spider Drassodes cupreus uses one of its several pairs of eyes as a polarization detector. In fact, the two eyes in this pair have polarization directions that are at right angles to one another. Suppose linearly polarized light with an intensity of 844 W/m2 shines from the sky onto the

Reduction of Light Intensity with Distance: Example Question

Inverse Square Law of Light - Intensity = Power / Area The law states that everytime the distance light travels is doubled, the intensity of that light is reduced to 1/4. Question: Demonstrate the reduction of light intensity with distance beginning with 1D equals 10 feet. What is the light density at 14 feet and at 20 fe

Ratio of intensity and amplitude

(a) What is the ratio of the intensity of an earthquake wave as it passes a point 28 km from the source to the intensity as it passes a point 7 km from the source? (b) What is the ratio of the amplitude of an earthquake wave as it passes a point 28 km from the source to the amplitude as it passes a point 7 km from the source?

Sound intensity example question

A ten-year exposure to the sound of a riveting machine will cause your threshhold of hearing to shift from 0 dB to 30 dB. What is the sound intensity corresponding to 30 dB? The normal lowest detectable intensity is 1.0 X 10 -12 W/m squared.

Intensity of Earthquake

(a) What is the ratio of the intensity of an earthquake wave as it passes a point 21 km from the source to the intensity as it passes a point 7 km from the source? (b) What is the ratio of the amplitude of an earthquake wave as it passes a point 21 km from the source to the amplitude as it passes a point 7 km from the source?

Diffraction of light: maximums by Grating

Please solve and explain An array of many identical slits placed close together with uniform spacing is called a grating. In a particular grating the slits are narrow enough to diffract the light passing through into a broad wavefront. The waves coming from the many slits interfere, producing bright spots on the screen wh

Interference Through Thin Films: Thickness of Soap Film

What is the thinnest soap film (excluding the case of zero thickness) that appears black when illuminated with light with a wavelength of 480nm? The index of refraction of the film is 1.33 and there is air on both sides of the film.

Intensity of Polarized Light

9 of 25 An FM radio station emits an electromagnetic wave which is received by a circuit containing a 3.33 x 10-7H inductor and a variable capacitor set at 7.31 x 10-12F. What is the frequency of the radio wave? 1.02 x 108 Hz 8.80 x 107 Hz 1.58 x 108 Hz 9.40 x 107 Hz 9.8 x 107 Hz 22 of 25 Linearly polarized ligh

Michelson iInterferometer

Draw a schematic diagram of a Michelson interferometer. Describe a setup that allows a pattern of circular interference fringes, localised at infinity, to be observed. For monochromatic light, derive an expression for the intensity of the interference fringes as a function of the angle θ of observation to the optical axi

Interference of Sound Waves: Destructive or Constructive

Two loudspeakers, A and B are driven by the same amplifier and emit sinusoidal waves in phase. Speaker B is 2.00 m to the right of speaker A. The frequency of the sound waves produced by the loudspeakers is 206 Hz. Consider point P between the speakers and along the line connecting them, a distance x to the right of speaker A. B

Interference of sound waves

Two loudspeakers emit sound waves along the x-axis. The sound has maximum intensity when the speakers are 20 cm apart. The sound intensity decreases as the distance between the speakers is increased, reaching zero at a separation of 60 cm. What is the wavelength of the sound? The answer is not 20 or 60.

Neurobiology

Describe what happens in the retina (at the cellular level) when you "get used to the dark. Why is it not possible to see color at night? Background: This question involves neurotransmitters and channels. Text for course is "from neuron to brain" if you have access.

Diffraction Grating: Example Problem

Light is incident on a diffraction grating that has 2750 lines/cm. The second-order spectrum over the visible range (400-700 nm) is to be limited to 1.75 cm along a screen that is at a distance L from the grating. What is the required value of L? The second order maximum is corresponding to m=2.

Waves/Superposition

Three identical loudspeakers play a 170 Hz tone in a room where the speed of sound is 340 m/s. You are standing 4 m in front of the middle speaker. At this point, the amplitude of the wave from each speaker is "a". a) What is the amplitude at this point? b) How far must speaker 2 be moved to the left to produce a maximum a

Lingt: Intensity and energy

You are standing 2.2 m from a 150 W light bulb. (a) If the pupil of your eye is a circle 5.1 mm in diameter, how much energy enters your eye per second? [Assume that 5.0% of the light bulb's power is converted to light.] (b) Repeat part (a) for the case of a 2.2 mm diameter laser beam with a power of 0.66 mW.