- #1

otterandseal1

- 16

- 0

What's the difference between distance and the square of the distance?

Many Thanks

Many Thanks

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- B
- Thread starter otterandseal1
- Start date

- #1

otterandseal1

- 16

- 0

What's the difference between distance and the square of the distance?

Many Thanks

Many Thanks

- #2

russ_watters

Mentor

- 22,053

- 9,149

uhh...one is squared?What's the difference between distance and the square of the distance?

You'll need to elaborate considerably about your question if we are going to be able to help you!

- #3

- 18,135

- 10,966

The square of the distance is bigger.What's the difference between distance and the square of the distance?

Many Thanks

I think you need to be more specific with your question. What is it you are trying to figure out?

EDIT: Ah, I see russ beat me to it

- #4

otterandseal1

- 16

- 0

Its to do with irradiance, I see textbooks saying "distance increases will result in irradiance decreasing" and "irradiance is inversely proportional to the square of the distance" What is the distance between the two? Sorry if I was too vague.The square of the distance is bigger.

I think you need to be more specific with your question. What is it you are trying to figure out?

EDIT: Ah, I see russ beat me to it

- #5

otterandseal1

- 16

- 0

Its to do with irradiance, I see textbooks saying "distance increases will result in irradiance decreasing" and "irradiance is inversely proportional to the square of the distance" What is the distance between the two? Sorry if I was too vague.uhh...one is squared?

You'll need to elaborate considerably about your question if we are going to be able to help you!

- #6

jtbell

Mentor

- 15,961

- 4,709

Unless the distance is < 1.The square of the distance is bigger.

- #7

russ_watters

Mentor

- 22,053

- 9,149

The distance in question is the distance between the source of light and what is receiving it.Its to do with irradiance, I see textbooks saying "distance increases will result in irradiance decreasing" and "irradiance is inversely proportional to the square of the distance" What is the distance between the two? Sorry if I was too vague.

...I'm still not sure that is what you are asking though...

- #8

otterandseal1

- 16

- 0

Yes, but sometimes it refers to the distance between a source of light and then generally the square of the distance. Are they the same things? If it's more helpful, the inverse square law is the square of the distance is inversely proportional to irradiance/illuminance. What does the square of the distance mean?The distance in question is the distance between the source of light and what is receiving it.

...I'm still not sure that is what you are asking though...

- #9

russ_watters

Mentor

- 22,053

- 9,149

"distance" is how far apart 2 points in space are. The Earth is about 150 million km from the sun, for example.Yes, but sometimes it refers to the distance between a source of light and then generally the square of the distance. Are they the same things?

Squaring something is just squaring it. 150 million km squared is 2.25 x 10If it's more helpful, the inverse square law is the square of the distance is inversely proportional to irradiance/illuminance. What does the square of the distance mean?

Maybe you are asking what physical meaning this new number has? It has none, it's just a partial piece of an equation. It is not itself a distance. Notice that it no longer has units of distance...but note what units it has?!

- #10

otterandseal1

- 16

- 0

Is the symbol 1/d^2 the square of a distance then?"distance" is how far apart 2 points in space are. The Earth is about 150 million km from the sun, for example.

Squaring something is just squaring it. 150 million km squared is 2.25 x 10^{16}km^{2}.

Maybe you are asking what physical meaning this new number has? It has none, it's just a partial piece of an equation. It is not itself a distance. Notice that it no longer has units of distance...but note what units it has?!

So if I said as the distance from a point source increases, the irradiance decreases, would this be an effective conclusion of the inverse square law?

- #11

sophiecentaur

Science Advisor

Gold Member

- 27,805

- 6,323

Near enough when the source can be regarded as a point source. An extended source like big nebulae or galaxies *Sun and Moon, too) need some adjustment.Is the symbol 1/d^2 the square of a distance then?

So if I said as the distance from a point source increases, the irradiance decreases, would this be an effective conclusion of the inverse square law?

Go into the garden at night and see the effect of the light from a picture window as you walk away, trying to read a book. Definitely not ISL.

- #12

russ_watters

Mentor

- 22,053

- 9,149

Yes. The irradiance decreases faster with a square in the equation than without. That's it.Is the symbol 1/d^2 the square of a distance then?

So if I said as the distance from a point source increases, the irradiance decreases, would this be an effective conclusion of the inverse square law?

- #13

otterandseal1

- 16

- 0

Sorry just to double check 1/d^2 is not the same as the square of the distance is it?Yes. The irradiance decreases faster with a square in the equation than without. That's it.

- #14

russ_watters

Mentor

- 22,053

- 9,149

No, it's 1 divided by the square of the distance.Sorry just to double check 1/d^2 is not the same as the square of the distance is it?

- #15

otterandseal1

- 16

- 0

In irradiance experiments, why is a black sheet placed underneath the light meter and the light bulb?No, it's 1 divided by the square of the distance.

- #16

russ_watters

Mentor

- 22,053

- 9,149

Probably to cut down on reflected light to make the experimental results better fit the inverse square law.In irradiance experiments, why is a black sheet placed underneath the light meter and the light bulb?

- #17

- 18,135

- 10,966

Hey, watch it! Nitpicking here is MY jobUnless the distance is < 1.

Share:

- Replies
- 18

- Views
- 1K

- Replies
- 6

- Views
- 740

- Replies
- 4

- Views
- 1K

- Replies
- 17

- Views
- 1K

- Last Post

- Replies
- 13

- Views
- 4K

- Last Post

- Replies
- 1

- Views
- 11K

- Last Post

- Replies
- 1

- Views
- 2K

- Replies
- 6

- Views
- 2K

- Replies
- 12

- Views
- 990

- Replies
- 5

- Views
- 981