Brightness Definition and 138 Threads

Homework Statement The circuit has identical light bulbs. A fourth identical light bulb is added to the circuit. How does the brightness of the original light bulbs change? a)All of them get dimmer b)X,Z get dimmer, Y brighter c)X,Z brighter, Y dimmer d)X,Y dimmer, Z brighter e)X,Y brighter, Z...

Homework Statement Hey guys, this is actually a question from my roommate's homework. She gave her response and I figured I'd check it over. I have some questions too! Consider the following statement made by a physics 480 student while pondering the fact that two bulbs connected in series...

Homework Statement A lamp is connected to the secondary part of an ideal transformer. What will happen to the brightness of the lamp if the number of turns in secondary coil is increased? Homework Equations Vs / Vp = Ns / Np = Ip / Is P = V.I = I2R = V2/R The Attempt at a Solution I have...

Question: Considering the effect of an Earth sized plaent transiting a star, and blocking its light. How big will the change in ABSOLUTE birghtness be for different stellar classs O and A, if we subtract off this blocked light. telescopes can detect very small changes in brightness...

Can someone please explain to me in simple words the process of calculation to measure the size and the distance of a star (or a galaxy for that matter)? What are the measured values? I have read about what I think could be two "relatively easy" measurable variables such as “apparent size” and...

I have a problem with some question I had to answer for the Surface Brightness \Sigma \propto \frac{Flux}{Angular~area}= \frac{F}{\Omega}. I was able to show that \Sigma \propto (1+z)^{-4} Then the question asks whether knowing its value for known candles or yardsticks, is a good way to...

Hi everyone, So, I am involved in a solar project for the developing world involving solar lights. What I would like some confirmation on is how to figure out how bright a LED light is going to be? I need the light to be bright enough for a child to study by, but unsure how to ensure this...

Hi again. We have two electric circuits. One is with a thin filament and the other has say 5 times larger filament. It is clear that the 5 times thicker filament is 5 times more powerful: the energy dissipation from electrons to the atoms is 5 times faster, because the current is higher 5...

Homework Statement This is a circuit i tried recently . I have recorded my observation below and i need to know why it happens like that .....230 V ______________(~)______________ |...........| |...........| |...........| |...62V...130V...38V...|...

Homework Statement Q. What will happen when a) A bulb rated 240 V 100W is connected to a 120 V supply . b) A bulb rated 120 V 100W is connected to a 240 V supply Homework Equations P = V2/R The Attempt at a Solution a) R = 2402/100 = 576Ω Power dissipated when the bulb is put across a...

Homework Statement Normally, household lightbulbs are connected in parallel to a power supply. Suppose a 40 W and a 60 W lightbulb are, instead, connected in series. (see here) Which bulb is brighter? Homework Equations P_{resistor}=I\Delta V=I^2R =\frac{(\Delta V)^2}{R} The Attempt at a...

I understand that generally, power and light bulb brightness are directly proportional. However, because there are so many ways to write the power formula (P=IV = I^2 * R = V^2 / R), I was a bit confused about what factors actually determine power and wanted to confirm whether the following is...

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. http://postimg.org/image/5dlx5a1p3/ Homework Equations V=IR => I=V/R The...

It is possible to convert brightness temperature of Earth surface (K) to the actual temperature? Is there any formulae for such conversion? Thanks in advance!

Can anyone offer insight into the derivation of the surface brightness to solar luminosity conversion S(mag/arcsec^2) = Mabs + 21.572 - 2.5log S (Solar luminosities/pc^2) More or less my concern is the constant term, is it empirically observed value or is there a derivation for it? thanks

What makes, for example, blue color appear darker or lighter? Is it just amount of photons (intensity) or is there any relation between brightness and wavelength? Or is there something else that comes into equation as well?

Homework Statement If a 6v incandescent globe is running at 6v with 0.6amps has a 0.909 resistor introduced into it's circuit which drops the voltage across it to 5.501v and 0.55amps how much does the brghtness change? The Attempt at a Solution 5.501*0.55/6*0.6 original brightness. Is it as...

Hello, I have two different materials, wood and iron in two different environments. I have both the wood and iron temperature, respectively Tw, and Ti. I also know their emissivities, Ew, and Ei. What I want to know is the temperature of the iron if it was wood (i.e. if its material was wood...

Assalamualaikum... << Islamic translation by Moderators: "Peace be unto you" >> hello everyone... i just want to know how to control the light brightness for automatically... what i know...in manual we can use a dimmer to control the light brightness..(correct me if i wrong)... if anyone can...

How bright could you possibly get a radioluminescent material to glow? Let's use tritium as the radionuclide. How would you mathematically calculate the brightness? What is the best radionuclide and phosphor to use? Obviously it has to be a β-emitter. Would it depend mainly on the β energy...

Hi everyone! I've been reading up on light and transmission, absorption and reflection and I was wondering how unpolarized sunglasses are able to reduce brightness. I tried Google-ing this but all I found was information about polarized sunglasses and how they reduce glare and work as UV...

If we consider two laser beams with identical 3 level energy level schemes except that the metastable state for one has a lifetime of 1μs and the other, 100μs. Which will give the brighter (more intense) beam? I gather that, since all things are identical up to the metastable state, the...

Homework Statement 20 bulbs are wired together in a series position. A) what happens if 10 more bulbs are added in series? B) the bulb was modified such that an additional resistor is placed across the filament (parallel to the filament). The value of the resistor R is much larger than the...

Hey, I have a question regarding practical electricity. Since we know that power (rate of energy released) determines brightness of bulb, then: Since P = VI and V = RI, it implies 1. P =(V^2) / R 2. P = (I^2) * R How can we tell if power increases or decreases when resistance (R) of...

Homework Statement The circuit has identical bulbs and an ideal battery. When bulb D is unscrewed from its socket (the socket remains in its place), what would happen to the brightness of bulb F? Homework Equations V = IR The Attempt at a Solution Since bulb D is unscrewed from it...

hi member! i would like to have your ideas on how to program my microcontroler to input a specific value to the light bulb so as the brightness to be as specific as i require, if any fore circuit is also required,i'm here to accept and utilise ideas

is it possible to create a program which can change the brightness of the computer?

Homework Statement An object gives out a spectral line of 919nm compared to that of 589nm in a laboratory. It has a brigtness of 1.2 x 10-11 W m-2. The objective is to find out the brightness of the object if it were at 700 Mpc. Homework Equations 1. Z (redshift)= change in wavelength...

headlights on starting car are brighter . they immediately get dimmer . why?

Where to find an exact formula for brightness temperature caculation? Only Wien's approximation is used everywhere. It is too crude for me.

For my physics house project, it says i have to have 2 lights connected in parallel with one switch and unequal brightness, using a resistor. Is there anyway to do this?

What does the brightness of a bulb depend on: power or current?

So I googled and found out that brightness of a lightbulb is directly related to current, but for some reason it doesn't match the concept I have in my head. I know that a lightbulb gets brighter as it gets hotter (like any kind of metal) So for a lightbulb to get brighter, it needs more...

I believe that it is the case that if I were on Pluto, say the sun would appear much smaller, the area of the disc I'd be looking at would be (R_Pluto/R_Earth)^2 times smaller than if I were looking at the sun from Earth. However,I heard today that that small little area as viewed from Pluto...

Homework Statement Rank in order of brightness, from brightest to dimmest. Homework Equations V=IR, Kirchoff's Laws The Attempt at a Solution I assumed the bulbs are supposed to be considered just as resistors, and that the more current through the resistor, the brighter the bulb. All...

Today in a lecture, prof asked that for 2 bulbs connected in series(100W and 40W), which was brighter? And the answer was the 40W bulb. His explanation was that we use P = I2 R. Higher power rating means higher R, and thus less bright. I argued that since P = VI, and I is constant, P is...

Hi ! If side by side, how much would Betelgeuse be brighter than Sun? I mean visible light. Thanks!

This is a problem intended to show us that Astronomers are sometimes fooled into thinking that a cosmic source of radiation is thermal, when it is not. Here is the problem: Consider a cosmic source emitting one hundred solar luminosities all within 1 MHz of the single frequency of 22 GHz...

hello Forum i am a novice physics learner. actually i want to calculate or construct an equation through which i can measure the maximum brightness of moon's light on our planet. can anyone give me any idea from where to start?

Since the black hole has infinite brightness near the singularity just below the photon sphere, would the big bang singularity also possesses such characteristic?

Homework Statement There are two bulbs, one of 100W and one of 50W and a 120V battery. First, connect them in parallel, find the resistance and current of each and determine which will shine brighter and by what factor. Next connect them in series, again find the resistance and current of each...

1. what is a qualitative comparison for the following diagram? http://img830.imageshack.us/i/picture1uq.png/ 2. V=IR 3. B=C>A

If I see 3 candles at 3 m across compared to 2 candles at 2 m across or 1 candle at 1 m across...does it make a difference in terms of brightness if more candles are seen at greater distances? Is the magnitude of light for all 3 situations the same?

Forgive me if this is the incorrect section of the forum for a question like this. If I already have used the CIE Chromaticity diagram to plot a color with dominant wavelength of 600 nm and maximal purity, how should I proceed to describe a color with half the intensity of said color -- i.e...

Homework Statement Two light bulbs of resistance R1=10 ohms and R2 = 15ohms are connected in series with a 25V battery. Which bulb glows more brightly? Now the bulbs are connected in parallel with the battery. Which bulb now glows more brightly? Homework Equations V=IR The...

EDIT: [SIZE="6"]NOT A HOMEWORK PROBLEM in a bulb increase in resistance means that there is a increase in brightness.if there is a decrease in resistance means that decrease in brightness. is the statement correct ? one more question does the brightness depend on current say we have same R ...

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...