11.11 Energy in waves: intensity  (Page 2/3)

Which measurement of a wave is most important when determining the wave's intensity?

Two identical waves undergo pure constructive interference. Is the resultant intensity twice that of the individual waves? Explain your answer.

Circular water waves decrease in amplitude as they move away from where a rock is dropped. Explain why.

Medical Application

Ultrasound of intensity $1\text{.}\text{50}\times {\text{10}}^2{\text{W/m}}^2$ is produced by the rectangular head of a medical imaging device measuring 3.00 by 5.00 cm. What is its power output?

The low-frequency speaker of a stereo set has a surface area of $0\text{.}\text{05}{\text{m}}^2$ and produces 1W of acoustical power. What is the intensity at the speaker? If the speaker projects sound uniformly in all directions, at what distance from the speaker is the intensity $0\text{.}1{\text{W/m}}^2$ ?

To increase intensity of a wave by a factor of 50, by what factor should the amplitude be increased?

Engineering Application

A device called an insolation meter is used to measure the intensity of sunlight has an area of 100 cm ² and registers 6.50 W. What is the intensity in ${\text{W/m}}^2$ ?

Astronomy Application

Energy from the Sun arrives at the top of the Earth’s atmosphere with an intensity of $1.30{\text{kW/m}}^2.$ How long does it take for $1.8\times {10}^9\text{J}$ to arrive on an area of $1\text{.}00{\text{m}}^2$ ?

Suppose you have a device that extracts energy from ocean breakers in direct proportion to their intensity. If the device produces 10.0 kW of power on a day when the breakers are 1.20 m high, how much will it produce when they are 0.600 m high?

Engineering Application

(a) A photovoltaic array of (solar cells) is 10.0% efficient in gathering solar energy and converting it to electricity. If the average intensity of sunlight on one day is $700{\text{W/m}}^2,$ what area should your array have to gather energy at the rate of 100 W? (b) What is the maximum cost of the array if it must pay for itself in two years of operation averaging 10.0 hours per day? Assume that it earns money at the rate of 9.00 ¢ per kilowatt-hour.

A microphone receiving a pure sound tone feeds an oscilloscope, producing a wave on its screen. If the sound intensity is originally $\text{2.00}\times {\text{10}}^{\text{–5}}{\text{W/m}}^2,$ but is turned up until the amplitude increases by 30.0%, what is the new intensity?

Medical Application

(a) What is the intensity in ${\text{W/m}}^2$ of a laser beam used to burn away cancerous tissue that, when 90.0% absorbed, puts 500 J of energy into a circular spot 2.00 mm in diameter in 4.00 s? (b) Discuss how this intensity compares to the average intensity of sunlight (about $700{\text{W/m}}^2$ ) and the implications that would have if the laser beam entered your eye. Note how your answer depends on the time duration of the exposure.