Light bulb Definition and 142 Threads

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...

Hi, Is it possible to make a standard light bulb light without any physical contact to it (appart from support)? I seem to remember seeing such an experiment, but can't remember the details. Thanks

How does one calculate efficiency for an incandescent light bulb? Assume the bulb is 40 W, has a tungsten filament at temp. ~ 2800 K. The bulb would be used for heating in a device. If we assume blackbody: From Wien's displacement law, the maximum wavelength is 9.99E-7 m. Fromt the...

Homework Statement How many Joules of energy does a 100 watt light bulb use per hour? How fast would a 70-kg person have to run to have that same amount of kinetic energy? Homework Equations How fast would a 70-kg person have to run to have the same amount of kinetic energy? The...

Homework Statement A 100 W incandescent light bulb converts approximately 2.5% of the electrical energy supplied to it into visible light. Assume that the average wavelength of the emitted light is λ = 530 nm, and that the light is radiated uniformily in all directions. How many photons per...

Can a halogen light bulb be powered by gas, or can a halogen light bulb only be powered by electricity? Can an incandescent light bulb be powered by gas, or can an incandescent light bulb only be powered by electricity?

Hey guys, was wondering if you could help me with this question: What determines the brightness of a lightbulb? I think it would be power (and therefor voltage and current since P = VI) as power is used in the measurement of energy delivered. Why is it the case then that, from the...

Homework Statement We did an experiment in class abvout resistance and temperature. The teacher told us to find out why light bulbs usually blow when you turn on the light. It must be related to the experiment we did which was seeing how resistance changed with temperature Homework...

Homework Statement First of all I apologise if this is in the wrong place. Anyway we have been given the task of finding out the efficiency of a solar panel, where energy from a light bulb is used to heat the water in the panel. I was just wondering if someone would just check that my...

Does it have an aura, or is the aura just a refraction defect of air?

Homework Statement I want to modelling a light bulb filament in MATLAB, but I don't know, what functions describe this shape. My question is, what are equation (x,y,z) which describe the light bulb filament.

Homework Statement What is the approximate electric field strength of the electromagnetic waves radiated by a 100-W light bulb, measured 3.0m from the bulb? Homework Equations $$\vec{E}=\frac{kq}{d^{2}}$$ $$P=\frac{2kq^{2}a^{2}}{3c^{3}}$$ The Attempt at a Solution I solved for...

So for my physics independent study project. I am studying the resistance vs. temperature in non-ohmic material. I passed different currents through the light bulb and took the surface temperature with a thermocouple. How can I find the temperature of filament using the surface temperature...

Homework Statement the tungsten filament of a light bulb has a resistance of .07 ohm. if the filament is 27 cm long, what is the diameter Homework Equations R= p(L/A) Area of a circular cross section = (PiD^2/4) The Attempt at a Solution R= p(L/A) A= (pL)/r...

Hey... This is for a school projecct ... Well... look i need to lighg up a little light bulb(like a christmass, those little ones) but i don't don't know how, i can't use any plugs in the wall or anything... i was thinking on using some batteries and wires but i still don't know how... If...

Hey... This is for a school projecct but i feel like its best fiting here... Well... look i need to lighg up a little light bulb(like a christmass, those little ones) but i don't don't know how, i can't use any plugs in the wall or anything... i was thinking on using some batteries and wires...

Why does passing current through Wolfram filament, heats the Wolfram filament in light bulb? What happens with the electrons?

Since oxidation is the reason for light bulb tungsten filament destruction in case of breach of the bulb envelope, while illuminated, what is the minimum oxygen required for oxidation to occur. Assume an automotive 12vdc bulb which has a greater diameter filament. However if it is considered...

ok, I know I always think my questions are going to be dumb, but this time I should really get some credit for how dumb it is. but I can't find the answer on the internet so here goes: This little lamp I have says "max 25W," does this mean that the maximum output of the lamp is 25W, so a...

Homework Statement The resistance of the tungsten filament in a light bulb changes with temperature according to equation (1), below. I am supposed to calculate the temperature of the light bulb at voltage 0.8280 volts and a current of 0.0853 amps. The bulb is connected to a 1.5915 volt...

Homework Statement The problem is that I cannot figure out why a filament will burn out in a particular spot. Higher resistance = lower current why does the filament heat up more? Homework Equations R2= R1[1+a(T2-T1)] Resistance = (resistivity * L)/ A R= V/I The Attempt at a...

Homework Statement You stand 2.7 m from a 150 W light bulb that converts 5% of the electrical energy dissipated within it to light. (a) If the pupil of your eye is 5 mm in diameter, how much energy enters you eye per second? ___J Homework Equations Iave= Pave/Area The Attempt...

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

http://www.teralab.co.uk/Experiments/Plasma/Plasma_Page1.htm" Check this out

A light bulb is completely covered with a thin coat of black soot in a room maintained at 20 degree celsius. If the shell has an equilibrium temperature of 100 degree celsius. What is the wattage of the bulb? I can't understand how to do it. I am a student of 9th standard.

Hi, I am stuck on this question, any help would be appreciated. Thanks! The tungsten filament of a certain 100 W light bulb radiates 2.85 W of light. (The other 97.15 is carried away by convection and conduction) The filament has surface area of 0.400 mm^2 and an emissivity of 0.952. Find...

Hi guys.. Would a light bulb's current and voltage change according to ohm's law? Thanks..

http://img224.imageshack.us/img224/5535/physics31id.png "Light bulbs with the wattage ratings shown in the figure above are connected in a circuit. (a) What current does the voltage source deliver to the circuit? (b) Find the power dissipated by each bulb. (Asusume normal operating resistances...

I have a great invention! It's great for many reasons! 1. I thought of it 2. People are lazy and will use it 3. Guys exist 4. Women are annoying 5. I thought of it What's the most annoying thing that one has to do in their life? The most mind-numbing, boring, stupid thing one will ever...

Why does an electric light bulb nearly always burns out just as you turn on the light, but almost never while the light is shining? :confused:

Well the question asked us to make a rough estimate of the temperature of the filament in an ordinary electric light bulb which emits white light. And if it has radiated power of 100 W, make a rough estimate of the surface area of filament. Well, the thing is how u make a rough estimation on...

You have a light bulb in the middle of a room and ... Hi people, here's an easy question for you. I was asked this by a guy down the pub a few days ago, I think I know the answer, but they don't believe me. If you have a light bulb switched on in the middle of a room and then you put mirrors...

I did a physics lab about diffraction grating where we had to determine the angular positions of all spectral lines of the helium discharge tube. I have 3 questions : 1. Why use a discharge tube instead of a light bulb? - I think it might be because you would have to break up the white...

Hey guys I am having some trouble with this simple questions: What is the resistance of a light bulb that uses an average power of 75.0 W when connected to a 60.0 Hz power source having a maximum voltage of 190 V? (b) What is the resistance of a 120 W bulb? I tried doing it by...

Hi all. I'm wondering how people determine the lifetime of a light bulb. Do they really turn on the bulb and wait till it go down? Or there are special methods to shorten the duration of the testing experiment? Anyone know?

True or false? Answer: http://www.snopes.com/science/lightbulb.asp

You are in a room with 3 light switches. These switches are connected to 3 separate light bulbs in an ajoining room. Access to the ajoining room is via a door that remains closed, there are no windows, other people etc etc. You are allowed to enter the ajoining room once and then return. At...

Q: How can the prisoners tell, with certainty, that all 100 of them have visited the central living room with the light bulb. The riddle: 100 prisoners are in solitary cells, unable to see, speak or communicate in any way from those solitary cells with each other. There's a central living...

Q: How many forum members does it takes to change a light bulb? A: * 1 to change the light bulb and to post that the light bulb has been changed * 14 to share similar experiences of changing light bulbs and how the light bulb could have been changed differently * 7 to caution about...

as part of a physics practical write up i have to measure the temperature of a light bulb envelopes temperature as the voltage increases. first ... am i right in thinking a type J exposed thermocouple would do the trick for this? if so, i heard something about one end being cold, to...

Hi all, I have two light bulbs, both for 230 volts. One has 100 watts, the other 15 watts. It is clear that the 15W bulb has the higher resistivity. But is its filament a) longer b) thinner c) both, and why? Thanks!

How may watts does a 60-watt light bulb use in three hours? 60*3=180watts?