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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.

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

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: 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

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

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.

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

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

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.

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.

Interference intensity by spherical waves

Two 1.0M-Hz radio antennas emitting in-phase are separated by 600m along a north-south line. A radio receiver placed 2.0 km east is equidistant from both the transmitting antennas and picks up a fairly strong signal. How far north should that receiver by moved if it is again to detect a signal nearly as strong. non-paraxial

Intensity of sound

By what amount does the intensity level decrease when you triple your distance from a source of sound?

Polarization

Completely polarized light is passed through a polarizing sheet. The light that passes though has an intensity of 50% of the incident beam. The angle between the direction of the polarization of the incident beam and the direction of the polarization of the sheet must be what?

Interference of light waves: Young's double slit experiment.

Imagine doing Young's two slit interference experiment with an average of one photon per second incident on the slits. If you cover one slit with your thumb every other second, will there be interference ? Why ? What's going on ? What pattern will you see if you average for a long time ?

Frequency of Bi-color LED

A bi-color LED alternates so that the color red emits at 60Hz and the color green emits at 60 Hz, so that visually it appears yellow. What frequency would it blink if you viewed it through a yellow filter? What frequency would it blink if you viewed it through a green filter?

Point source of light

Consider a point source of light. How would the intensity of light vary with distance from the source according to a) wave theory and b) particle or photon theory? Explain.

Sound Intensity of Twenty Violins Playing Simultaneously

Twenty violins playing simultaneously with the same intensity combine to give an intensity level of 82.5 dB. (a) What is the intensity level of each violin? (b) If the number is increased to 40, will the combined intensity level be more than, less than, or equal to 165 dB? explain

Sound Intensity Relations

Sound 1 has an intensity of 380.0 W/m^2. Sound 2 has an intensity level that is 2.5 dB greater than the intensity level of sound 1. What is the intensity of sound 2?

Sound Intensity Levels

The distance to a point source is tripled. (a) By what factor does the intensity decrease? (b) By what amount does the intensity level decrease?

What is the sound intensity in the room?

If I have the television on and the sound level is 60 dB, then my wife starts the vacuum which is 74 dB, then the baby starts crying at 78 dB, what is the total sound level in the room? And what is the total intensity?

Child Screaming

A mother hears a child scream from across the room, 23 feet away. The sound pressure level is 72dB. When she holds the child on her shoulder, her ear is 3 inches from the screams. Using the decibel chart, about how long until damage to her hearing occurs if the child continues screaming? http://www.gcaudio.com/resources/howto

Polarization of Light Waves

Unpolarized light passes through two polaroid sheets. The axis of the first is vertical, and that of the second is at 26.0° to the vertical. What fraction of the initial light is transmitted?