# Unit Conversion - Flux Densities

• deedsy
In summary: However, if they are not visible magnitudes, I would use the wavelength of the light they emit. So, if they are emitting in the visible spectrum, I would use 0.55 μm as the wavelength, and if they are emitting in the infrared spectrum, I would use 1.0 μm as the wavelength.
deedsy

## Homework Statement

I need to convert from a fv in units of Jy to fλ in units of erg s^-1 cm ^-2 A^-1

fv = 1.0254e-2 Jy

## Homework Equations

fv dv = fλ dλ
fλ = fv dv/dλ
and because v = c/λ...

fλ = fv*c / λ^2

Also 1 Jy = 10^-23 erg cm^-2 s^-1 Hz ^-1

## The Attempt at a Solution

fλ = [(1.0254e-2 Jy)(10^-23 erg cm^-2 s^-1 Hz ^-1) (3e10 cm/s)(1A/10^-8 cm)] / [1 A^2]

*note: A = angstrom units

my final answer was fλ = 3.0762e-7 erg s^-1 cm^-2 A^-1

But I checked my answer on an online converter and it was wrong, but I don't know why because all my units canceled out correctly.

You have done the conversion as though your given fv was measured at a wavelength of 1A. I doubt this is the case. When you put in the c/λ^2 factor, you need to do it at the wavelength (frequency) of the measurement. Was this given?

phyzguy said:
You have done the conversion as though your given fv was measured at a wavelength of 1A. I doubt this is the case. When you put in the c/λ^2 factor, you need to do it at the wavelength (frequency) of the measurement. Was this given?

The first part of the question had us convert a magnitude (12) into fv given a zero point for the magnitude system (fv=647 Jy). So I used m-m0 = -2.5 (f/f0) to solve for f where m0 = 0 and f0 = 647 Jy and m =12. This gave a value of fv = 1.0254e-2 Jy. Then we just have to convert that value into fλ

Here's the question as it appears on the assignment:
Given that the zeropoint of the magnitude system is fv=647 Jy. Find the flux density of a 12th magnitude star in Janskeys (which is in fv) and then convert it to fλ (in units of ergs^-1cm^-2A^-1)(ignore any minus signs in the conversion).That's all the information I have.

Well, I may be wrong, but I think you have to assume some wavelength to do the conversion. If they are visible magnitudes, I would use the center of the V band, which is at 0.55 μm.

1 person

Your attempt at a solution seems to be correct. It is possible that the online converter you used may have used slightly different conversion factors or rounding errors, resulting in a slightly different answer. However, your method and units appear to be correct. I would suggest double checking your calculations and the conversion factors you used, and perhaps try using a different online converter to confirm your answer. It is also always a good idea to include units in your final answer to ensure accuracy and avoid confusion. Keep up the good work!

## 1. What is unit conversion in flux densities?

Unit conversion in flux densities refers to the process of converting flux density measurements from one unit to another. Flux density is a measure of the amount of energy passing through a unit area per unit time and is commonly used in physics and engineering.

## 2. Why is unit conversion important in flux densities?

Unit conversion is important in flux densities because different units can be used to measure the same quantity, and it is necessary to convert between these units in order to make accurate comparisons and calculations. It also allows for easier communication and standardization in scientific research and applications.

## 3. What are the most commonly used units for measuring flux densities?

The most commonly used units for measuring flux densities are watts per square meter (W/m²) and watts per square centimeter (W/cm²). Other units such as watts per square foot (W/ft²) and watts per square inch (W/in²) may also be used in specific industries or applications.

## 4. How do you convert between different units of flux densities?

To convert between different units of flux densities, you can use conversion factors or equations specific to the units you are converting between. For example, to convert from W/m² to W/cm², you can multiply the value in W/m² by 10,000. It is important to pay attention to the units and ensure that they are consistent throughout the calculation.

## 5. Are there any online tools or resources available for unit conversion in flux densities?

Yes, there are many online tools and resources available for unit conversion in flux densities. These include unit conversion calculators, conversion tables, and educational websites that provide step-by-step instructions for converting between different units. It is important to double-check the accuracy of the tools and resources used for conversion to ensure the most precise results.

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