# Anyone Good in Physics!? Help needed on a few questions.

Discussion in 'BlackHat Lounge' started by maxxwilliams, Feb 13, 2012.

1. ### maxxwilliamsJunior Member

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Hi all. Here I will post a few questions on physics and light. If anyone can help me and has time to explain how they get the answers, let me know

1. Yellow light has a wavelength of 575 nm (nanometers). What is its approximate frequency?
A. 5 x 10^12 Hz
B. 2 x 10^14 Hz
C. 5 x 10^14 Hz
D. 5 x 10^15 Hz

2. If a blackbody is heated to a temperature T (in degrees Kelvin, K, where K = âˆ˜C + 273), the wavelength where it appears brightest (the peak of the blackbody curve) occurs at a wavelength, Î»peak (in METERS), given by Wien's Law:
Î»peak x T = 0.0029
From Wien's Law above, at what wavelength, Î»peak, does a chair at room temperature (T=290 K) look brightest?

A. 10 meters
B. 10^-3 meters
C. 10^-4 meters
D. 10^-5 meters

3. Referring to your answer from Question 2 (the Wien's Law problem), what is the corresponding frequency of that radiation?

A. 3x10^13 Hz
B. 4x10^13 Hz
C. 5x10^14 Hz
D. 5x10^15 Hz

4. Referring once again to the Wien's law question 2, in what part of the radiation spectrum does the peak radiation occur?
A. Visible
B. Infrared
C. Ultraviolet
D. X-rays

**Any help would be appreciate it. I think I know some of the answers, but I am trying to double check. Thanks in advance.

2. ### BlueNebulaJunior Member

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Question 1. is C. 5 x 10^14 Hz

3. ### nesterdwarfRegular Member

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1. B
Code:
`http://answers.yahoo.com/question/index?qid=20091129202534AALzkuk`
2. D
x(290) = .0029
x = .0029/290
x = 10^-5 meters

3. A
(3 x (10^8)) / (10^(-5)) = 3.0 × 10^13

4. B
Code:
`http://hyperphysics.phy-astr.gsu.edu/hbase/ems3.html#c1`
Depending on how much the big G likes me today, should be right. Could be completely wrong though...

ND

4. ### maxxwilliamsJunior Member

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Hey ND, that would make #1 C. I think you have a typo there. Thanks for response Blue and ND.

5. ### Virus1Supreme Member

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Welcome to Black Hat World........................
I use to be a physics tutor.... a long time ago.

Let's see if I remember.

speed of light = wavelength x frequency
3 x 10^8 = wavelength x frequency

wavelength=575 nm
if converted to meters is 5.75 x 10^-7 Meters

so solving for frequency:
Frequency = speed of light /wavelength= 3x10^8 / 5.75 x 10^ -7 = 5.2 x 10 ^14 Hz

So "C" seems to be the correct answer.

Double check this answer... i did it from memory.... no google used.

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