1) What is the decibel level of a sound whose intensity is 4% that of a 95 dB so

Question

1) What is the decibel level of a sound whose intensity is 4% that of a 95 dB sound?

2) How many dark fringes can be observed in the diraction pattern produced by a single slit of width 2.3micrometers with green light of 532 nm wavelength?

3) An unpolarised light beam of 2 mm diameter carrying 4 mW of power passes through two polarisers. The intensity after the second polariser is 75 W/m^2. What is the angle between the axes of the two polarisers?

4) In 2003, Itlaian households consumed a total of 153.6*10^-15J of energy (the largest amount of any sector in the Italians economy). How many days would it take for the sun to put that amount of energy onto a region 20 km by 20 km (0.15% of Italian's total land area)? Assume that energy from the sun arrives at the surface of the earth with an average intensity of 685 W/m^2

5) In a darkened room, a burning candle is placed 1.50 m from a white wall. A lens is placed between candle and wall at a location that causes a larger, inverted image to form on the wall. When the lens is moved 90.0cm toward the wall, another image of the candle is formed. Find (a) the two object distances that produce the specied images and (b) the focal length of the lens. (c) Characterize the second image [is the image real/virtual? Upright/inverted? Magnied/diminished? What is the magnication?] (Textbook problem from Physics for Scientists and Engineers 7th ed. by Serway and Jewett.)

6) A diverging lens of 6 mm focal length produces an image of magnication m = 1/2. What is the distance between the object and the lens?

7) (a) Find the angle between the first minima for the two sodium vapour lines, which have wavelengths of 589.1 and 589.6 nm, when they fall upon a single slit of width 2.00micrometers. (b) What is the distance between these minima if the diraction pattern falls on a screen 1.00 m from the slit? (c) Discuss the ease or diculty of measuring such a distance.

8) What is the power in diopters of a convex security mirror that has -5.25 m focal length?

9)(a) Where does an object need to be placed relative to a microscope for its 0.500 cm focal length objective to produce a magnication of 400? (b) Where should the 5.00 cm focal length eyepiece be placed to produce a further fourfold (4.00) magnication?

Explanation / Answer

I will answer 5 of these for the 1500 points...

Number 1)

Apply B = 10log(I/Io)

95 = 10log(I/(1 X 10-12)

I = 3.16 X 10-3 W/m2

New I = (.04)(3.16 X 10-3)

I = 1.26 X 10-4 W/m2

Then B = 10log(1.26 X 10-4/1 X 10-12)

B = 81.0 dB

Number 2)

Apply 1 = m(wavelength)/a

1 = m(532 X 10-9)/(2.3 X 10-6)

m = 4.32 (eliminate the decimal)

m = 4

Number 3)

First Find Intensity

I = P/A = (4 x 10-3)/pi(.001)2

I = 1273 W/m2

Then I = .5(Io)(cos2(angle))

75 = .5(1273)(cos 2(angle)

angle = 69.9o

Number 6)

Start with M = -q/p

1/2 = -q/p

p = -2q

Then 1/f = 1/p + 1/q

1/-6 = 1/-2q + 1/q

1/-6 = -1/-2q

2q = -6

q = -3

p = -2q = -2(-3)

p = 6 mm

Number 8)

D = 1/f

D = 1/-5.25

D = -.190

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