Brightness Definition and 147 Threads

Homework Statement Consider a circuit containing five identical light bulbs and an ideal battery. Assume that the resistance of each light bulb remains constant. Rank the bulbs (A through E) based on their brightness. Rank from brightest to dimmest. To rank items as equivalent, overlap them...

ok revision question fo me, just want to check my reasonning. which of te bulbs on the circuit of the attatched file will shine more brightly? i think p....because s and t r and q are in parrellel which is resistance 1/Rs+Rt+1/Rr+Rq where Rp is the sum of the resistance of 1/Rs+Rt+1/Rr+Rq...

Quick question, if i had a circuit of 5 light bulbs whereby 4 were running parellel in a sequence and one was running seperatly, would one be brighter than the others? sorry if it is hard to visulise :)

Homework Statement A light bulbs brightness can be measured by its power consumption. This in turn will depend on the I, V and R of the light bulb. The light bulb is rated at a power consumption of 1.0W when placed at a voltage of 6.0V. We change the battery from a 6.0V to a 3.0V one. Will...

Hello, I have a question about sunspots, to which the answer i could not find using google. Is the solar brightness dependant on how many solarspots are on the solar surface? I know that sunspots are cooler than the rest of the solar surface, however, the faculas that exist next to solar...

Homework Statement Rank the lightbulbs in order of brighness. http://img641.imageshack.us/img641/5871/lightbulb.png Homework Equations All lightbulbs are identical. The Attempt at a Solution A is brightest, then B=C, then D=E A>B=C>D=E B and C are the same...

Okay, I know that the brightness of light dims by 1 / r^2. I just need a little help about brightness and so forth. What exactly is the unit of brightness ? Also, when using 1 / r^2 Say I am 5 meters away from a light bulb and find the brightness, then I step back 47 meters. Would I just...

1. Go to http://www.matter.org.uk/schools/Content/Interference/gratingExplored.html . Q1. What is the effect of varying the Wavelength of the light? The attempt at a solution. The smaller the wavelength, the lesser the degree of diffraction, as evidenced by the narrower intensity envelope...

The bulb connected to the input of a step-up transformer is less bright than a similar bulb connected to its output. Why?

I have been wondering 1. We know that light has a wave-particle duality. Does the "light" here mean electromagnetic radiation, or just visible lights? 2. If it EMR exhibits wave-particle duality, does that mean radio waves are transmitted in form of photons? 3. and finally, I was reading...

Homework Statement A supernova remnant has an angular diameter \theta = 4.3 arc minutes and a flux at 100MHz of F_{100} = 1.6×10^{-22}J s^{-1}m^{-2}Hz^{-1}. Assume that the emission is thermal. (a) What is the brightness temperature, T_b? (b) Suppose that the emitting region were actually...

Homework Statement This is not a specific problem, but I am wondering, what exactly determines the brightness of identical bulbs? The current going through it? The voltage? Something else? Thanks. Homework Equations N/A The Attempt at a Solution N/A

I observed the ISS when it was almost overhead and well inside Earth's shadow with binoculars. The brightness was perhaps magnitude 8 or so, I'm not sure. I observed the ISS enter the Earth's shadow when it was at 60 degrees over the horizon, the brightness declined rapidly as it entered the...

Homework Statement A bulb emits a continuous spectrum of ultraviolet, visible and infrared light in the wavelength range 360nm to 2000nm. Assume that the light from this bulb is incident on a diffraction grating with slit spacing d and that the first-order brightness maximum for the wavelength...

Homework Statement How do the bulb's brightness compare? Which ones will be brighter or dimmer? What will happen if a resistor is placed before Bulb 2? and What will happen if a resistor is placed between Bulb 2 and 3? Does it matter if i place the resistor before or after the ammeter? Will...

Hi all, there are a few questions regarding the incandescent light bulb, which I believe are rather elementary, but has nevertheless been bothering me for quite some time. I don't know if my chain of thought is correct, please point out my mistakes if there's any. Thanks! Here goes (they are...

I'm looking at a problem where a battery of negligible internal resistance is connected to two lamps L and N in parallel with each other, then through in series to a 3rd lamp M. The question asks if the filament of one of the lamps in parallel N breaks then what happens to the brightness of the...

Hi, I feel extremely stupid for having to have this explained to me, but I am really confused by it. I recently encounter a proof of the fact that the brightness (energy/(time x area x solid angle x frequency)) of a black body can only depend on its temperature, not the properties of the...

Hello, I've been thinking over for some time about creating a programmable LED display. I have an EEPROM and microprocessor among other things already, so it's not like I'm buying all the parts. Ideally, this display would be viewable from up to 30-40 feet away so it will have...

Hi everybody, I have a very quick question about surface brightness profiles for an edge-on galactic disk. I have surface brightness values (V-band, not that it matters) in units of mag/arcsec^2 as usual, as a function of z, which is the distance from the galactic disk's plane. I'd like to...

Hi, Say we had two identical stars one light year away from us, but one is stationary and the other is receding from us at 0.8c. What would be the apparent brightness of the receding star relative to the stationary star? I think at least two effects would have to taken into account. 1)...

Hi, does the thickness of filament affect the brightness of a bulb? So will a thinner filament be brighter than a thicker filament?

Anyone know a good site to check up on how the star algol varies in brightness and how long its average cycle is?

I don’t see that this question has been asked before and I am hoping the generous moderators of this forum will be able to answer it. Suppose you have the “standard” situation with the man M on the embankment and the woman W in the center of the moving train car. (The train has lots of...

Homework Statement A variable star changes in brightness by a factor of 4. What is the change in magnitude?Homework Equations m and n represent two stars of magnitude m-n=2.5 log(f(n)/f(m)) log (f(n)/f(m))=.4*(m-n) The Attempt at a Solution I think m-n is suppose to represent a change in...

Can someone help me with 1 (e) at the following site: http://ocw.mit.edu/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/29B6C858-A92B-431F-A43E-725D58A768EF/0/exam1.pdf The solutions say that all on-bulbs in 1 (e) glow with equal brightness. But how is that possible because...

Homework Statement I'm trying to find the central luminosity per square parsec of a galaxy with central surface brightness I(0) = 15 \; mag \; arcsec^{-1}. I need the answer to be in multiples of the solar bolometric luminosity per square parsec. Homework Equations m_1 - m_2 =...

In general, does more current/less resistence mean the brighter of the light bulb? How does voltage take into account in this case

when light hits a surface at an angle. it is darker if it hits it at higher angle(facing away) than at a lower angle(facing towards). 1 Is there a formula for the brightness.The relationship of angle to brightness does not look linear...

I'm trying to get a grasp of the basics of a Tolman SB test. Please correct me if I'm wrong: To be able to do a Tolman SB test you first have to observe a couple of identical objects at different redshifts. "Identical" here means objects of the same spectral type and luminosity class. Then...

Tolman Surface Brightness Test -- need help! Richard Tolman derived that in an expanding universe with any arbitrary geometry, the surface brightness of a set of identical objects will decrease by (1+z)^4. I have two questions: 1) The surface brightness is the same as the flux (W/m^2)...

Tolman surface brightness test -- need help! Richard Tolman derived that in an expanding universe with any arbitrary geometry, the surface brightness of a set of identical objects will decrease by (1+z)^4. I have two questions: 1) The surface brightness is the same as the flux (W/m^2), right...

Homework Statement Show that the Hubble profile of surface brightness I(r) = I_0 \left(1+\frac{r}{R}\right)^{-2} leads to an infinite total luminosity, while the law I = I_0 exp[-(r/a)^{1/4}], with a a constant, does not. Here I_0 and R are constants and r is the distance from the centre...

Hello, I was wondering if someone might be able to diagnose and help me correct a problem I have with viewing videos online. It really is, i think, when I try to play .avi files? For example, when somebody links to a video on google, when I play it, the images is waaay to dark for my...

it is observed that Mars is somewhat brighter when in opposition (ie. sun- Earth - Mars in that order) that at other times. How can this be explained using a) The Ptolemaic model and b) The Copernican model of the solar system. (Assume that Ptolomy's construction describes the actual motion...

we have radiation contained within a spectral band of width delta lambbda such tha (delta lambda)/lambda = (10^-4) the laser beam has a diameter of 50 micrometers and it has a divergence in both the horizontal and vertical directions of 10 millirads. we need to calculate the spectral brightness...

Why does the face on surface brightness profile of spiral galaxies follow an exponential decrease with incresing distance from the center? Why is it exponential as opposed to linear or some power law? seems like 'e' shows up a lot. I know it is an obervational fact that they exhibit this...

i don't get it. really large stars are unstable and there are frequent outbursts. so they are called variable stars. but when they burst they create a nebula and remain as a star right? how is that? shouldn't they turn into a black hole or a nutron star or just a nebula? or do they just vary...

how does the size of planet eclipsing a star effect the brightness of the star? thanks.

:cry: hi i got 2 questions here fairly confusing was wondering if i can get some help thanks 1. consider a series RLC circuit in which R is an incandescent Lamp C is some fixed capacitor and L is a variable inductance. The source is 240 V ac. explain why the lamp glows brightly for some...

Claims universe not expanding: http://www.arxiv.org/abs/astro-ph/0509611 Another recent article about redshifts being apparently wrong: Research on candidates for non-cosmological redshifts "The paradox of apparent optical associations of galaxies with very different redshifts, the...

Hey, I've got a question which I hope you guys can help me with. It is observed that Mars is somewhat brighter when in opposition (ie. sun- Earth - Mars in that order) that at other times. How can this be explained using a) The Ptolemaic model and b) The Copernican model of the solar...

We have two bulbs, X and Y. Y has thinner and longer filament than X. When connected to a power supply which bulb will give out most light and why? I think the answer should be Y as it has heigher resistance and therefore will dissipate more energy. Thanks in advance. :approve:

Assuming there are five identical light bulbs. Light bulb C and D are in a series connection. C and D are in a parallel connection with E. Light Bulb A and B are in a parallel connection. The two parallel connections are wired in a series connection. What would be their relative brightness? I'm...

There are five light bulbs. Light bulb C and D are in a series connection. C and D are in a parallel connection with E. Light Bulb A and B are in a parallel connection. The two parallel connections are wired in a series connection. What would be their relative brightness? I'm thinking that...

It's amazing to realize that the world out there, beyond our retinas, is not at all bright even on a cloudless day in Arizona! And what's even more amazing is that even on a moonless night in a desert, the world "out there" isn't at all dark! It's our brains that manufacture brightness and...

I have difficulties to compare different brightness data of the sky. In older literature I found different measurements of the brightness density of the sky. Some of the results are shown in in m(vis)/deg^2 and others in asb. In order to compare the data in units of m(vis)/sterad, I...