What is Bulb: Definition and 283 Discussions

My textbook says a bulb glows brighter due to its high resistance. But it also says a bulb glows brighter when a larger current flows through it. Which is correct?

Wet bulb temperature is the lowest thermodynamic temperature of air that can be achieved at ambient condition, by creating 100% relative humidity in the immediate surrounding of the thermometer using cotton wick. As Wikipedia says "By contrast, the dew point is the temperature to which the...

Please view the youtube video below: This is not a homework problem. The reason seems rather weird. Though the video seems incomplete, I would like to know the reason why 39.2 Ohms showed up. It seems rather weird. I know that resistance does not depend on the Voltage or the current if I am...

Now, to be honest, I can comfortably light it with TWO piece of wires and not ONE. So , was it a trick question? Technically, those are havard grads. Please weigh in.

Homework Statement These questions are related to an experiment where we had to record the current for varying values of potential difference (10 readings), then repeat the process with the applied potential difference was reversed a) Why is the resistance of a light bulb not constant? b) Does...

Is there any physical law that prevents the electrons in the filament of a light bulb from emitting light? How come we always see light? What are the probabilities that all the electrons in the filament fail to emit light at the same time? I suppose there is a conservation law somewhere...

I put a light bulb inside a box and make it glow, is there a way to know where the light bulb is if the box is closed and not transparent

Homework Statement All bulbs are identical, (no information given on resistance so assuming all the same) All the switches are closed and then S1 is opened, Does bulb 6 get brighter, dimmer or stay the same? Does bulb 4 get brighter, dimmer or stay the same? Explain briefly why. Homework...

I understand that one would use a vacuum pump to evacuate a light bulb, but once a vacuum is created, how is the bulb sealed without air coming in?

I'm sorry to reopen the debate on what happens when I put a light bulb in a microvawe oven, but the question is driving me crazy. I'm debating with other students about "why I light bulb lights up when I put it in a microwave oven ?". I read the old thread posted in 2003...

I am trying to repair a A15 LED Bulb rated 5 WATT 46 MA 120 Volt. It runs on 30 Volt DC it has 5 cells inside one is not working so based on this information each cell needs 6 volts so the remaining 4 good cells will burn with 24 volts which I applied and my ammeter says 90 MA I know not how...

, the question was: if a elliptical shaped bulb , which was covered from outside and internally reflected light in the bulb itself . what would happen if it were placed in a vacuum ? would it emmit light for eternity ? hope someone would shed some light on the matter ?:) , and explain this...

Homework Statement Dry-bulb Temperature 46'C Wet-bulb Temperature 34'C P=101.3kPa with these, I have to 'calculate' Specific Humidity(w), Relative humidity(φ), Specific Enthalpy(h)Homework Equations Specific Humidity w=0.622*Pv/Pa when Pa=P-Pv Relative Humidity φ=w*P/[(0.622+w)*Pg] Specific...

hi, so i want to ask why is the inert gas pressure in an incandescent bulb should be low? i thought that when the gas pressure is high, more 'free' tungsten atoms can collide with the gas particles (since the gas particles move at higher speed) and bounce right back towards the filament. hence...

In an argument re an incandescent bulb, yeah those things, will flicker at 100Hz or 50Hz given a 50Hz mains power.The reasoning is the peak and trough of the sine wave both deliver a peak in candescence ie two peaks per cycle therefore 100Hz flicker?? Will be settled by experiment soon as we...

Homework Statement You have a light bulb where the filament (in vacuum space) starts to glow. This light hits the glass of the bulb at 90 degrees from distance R and is transmitted through the glass of thickness s into the air, of index of refraction nair. So light travels like this: vacuum...

Hello, new to the forum, just a average guy, not too much more informed on physics then the average person, so this will be a pretty simple question, anyway, to my question: with halogen bulbs, does higher wattage always mean thicker filament? Because i am trying to work out if tricky Chinese...

I was installing a new bulb with a switch in my house. There was two different ways to connect the bulb and the switch as shown in the picture. Which one is better and Why?

Hello there. I was looking for a place on the web where someone with an electrical understanding might be able to help me. I have a gas powered scooter which I wanted to make a change to the lighting circuit. My question is regarding the resistor in the circuit. With this circuit, while the...

Homework Statement If you measure the resistance of the three lightbulbs (independently) and get the following values. What is the equivalent total resistance of the circuit, and it’s uncertainty. R_1 = (50 \pm 7) \Omega, \ \ R_2 = (720 \pm 30) \Omega, \ \ R_3 = 140 \pm 20) \Omega Now you...

Homework Statement What is the voltage of the bulb D? Given the total voltage supplied by the cells is 4 watts and each bulb is identical and has a resistance of 3 ohms Homework Equations V=IR The Attempt at a Solution By assuming bulb A,B, and C as a group , their effective resistance would...

Guys i noticed something i can't explain, i was playing with a magnet while i was studying and my hand, where the magnet was, remained near the light bulb for some seconds, soon enough i realized that a strange sound was emitting then when i moved away my hand the emission stopped. What's the...

Random question, folks. A friend of mine lost power in his house this past evening, yet his front porch light, an LED bulb, is still shining bright. Any idea why this might be? Do they sell bulbs with some sort of backup battery built in? Edit: Apparently the light on one of his power strips...

Homework Statement How large an inductance should be connected in series with a 120 volt (rms), 60 watt light bulb if it is to operate normally when the combination is connected across a 240 volt, 60 Hz line? (First determine the inductive reactance required. You may neglect the resistance of...

http://www.bbc.com/news/technology-32101473 The BBC reports that a graphene light bulb will go on sale. What are its advantages over current technologies?

I came across a question: Four bulbs with different power rating, bulb A (240V, 40W), bulb B (110V, 36W), bulb C (12V, 60W) and bulb D (6V, 0.5W) are connected to relevant power sources. Which bulb is the brightest. At first, i thought the highest power will be the brightest. But the answer is...

Homework Statement Hey, so there is a light bulb above a tank of water which has a mirror at the bottom. I am trying to find the apparent depth of the image of the light produced by the mirror. Finding the apparent depth of the mirror is easy, but I am confused on what to consider the object...

I am having some trouble with discerning whether current (electrons flowing through the Tungsten), or the energy transfer as described by the poynting vector, is responsible for lighting the lightbulb.

Hi again - partially stuck with a question and I'm not sure where to go. Hoping someone would be able to give me a hint :) A 75 W non-inductive light bulb is designed to run from an ac supply of 120 V rms to 50 Hz. If the only supply available is 240 V rms show that the bulb can be run at the...

quick question when a light source is moving at a good clip like the above where the light bulb is moving at half the speed of light am I wrong in the drawing that the light halo would be lagging towards the back but even on the two sides? what I'm wondering is how long would the light behind...

Homework Statement X . . . . .Rope . . . . Bulb >>> Light -----> V Hot bulb is making rotation . Exist C + V ? Michelson Morley X1..............solar system Not exist C+V = only Source is making rotation around X1 ? X1 - far far point in space Homework Equations C = 300...

Homework Statement The asker needs to know the angles to mount three LEDs inside a traditional mains powered light bulb shaped enclosure "to get even radiation from the LEDs", and also the position of the covering plastic sphere in relation to the LEDs. (I was thinking that the position of the...

Homework Statement Why is the resistance lower in a bulb which is turned on? (Compared to when it has been off) One bulb which is off has a measured resistance of ##27.0 M\Omega## When it is on it has a measured resistance of #380.9375 \Omega## Homework Equations ##\rho (T)=\rho_o(1+\alpha...

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 What will happen if the middle bulb in the picture attached burns out? I thought the light intensity of the other two bulbs would increase since there is now more current passing through the two bulbs that are not burned out. Originally there is a current of I = V/R...

Homework Statement A triac is used in a dimmer switch to control a 100W light bulb. If the firing angle is set for α=∏/3 estimate the power dissipated in the bulb Rated at 100W and the voltage source 230V @ 50Hz. Homework Equations Vpeak = Vrms/0.707 The Attempt at a Solution...

anyone know what the metal fin-like structures are? i see these on a lot of LED bulbs. they look like heat sinks but if conventional bulbs don't need heat sinks why would an LED bulb need one? besides! i thought the conductivity of semiconductors was proportional to temp.

Homework Statement A light bulb has an internal filament with a total surface area of 2.5 X 10-3 ft2 that operates at a temperature of 2240 F. The filament has an emissivity of 1.0 and radiates through a vacuum to the glass wall of the bulb. Only 10 percent of the total energy emitted as...

Hi Folks, We use a UV bulb in my workplace which contains deuterium gas. The bulb is safely contained within a housing unit inside a machine so there are no direct hazards with UV radiation etc. I was however wondering, what would happen should such a bulb break? I have checked some MSDS...

Homework Statement In the figure below, you will attach one or more light bulbs of R=30.12 Ω in parallel with the battery (with ε = 20 V, internal resistance r). (i will upload with work and the picture of the wiring diagram) a.) For an ideal battery (r=0), what would be power...

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...

So I have a typical 9volt battery attached to a Christmas light and am attempting to demonstrate the typical "saltwater can conduct electricity" gimmick by showing that the bulb lights when completing the circuit in the solution. I'm racking my brain though and can't figure out why the bulb...

Hi guys, For a science experiment I've got to measure the power consumption of my circuit of a 100W incandescent light bulb connected to the mains AC, with a dimmer switch to vary its brightness. I was planning on just using one of those plug-in energy monitors with a digital display but...

Hi, I would like to ask a question on incandescent light. From the Thermionic emission (Edison effect), heated tungsten filament emits electrons that could be collected by an anode (like a foil connected to positive voltage). The wiki also mentions that in order to facilitate...

If you have a light bulb that weighs 10 g when empty, how does adding an ideal gas inside of it change the mass? If I'm not mistaken, the force the gas exerts on the light bulb (well, a perfectly symmetrical object is a better example) is the pressure, and it would be pointing in all...

Hello, I'm trying to apply conservation of energy to a lightbulb circuit, but I can't think of what term should be included for heat loss / convection / conduction Here's what I've got Pin = Pradiated + i2Rwire, connections, etc + Power lost to heating surroundings? (what can I use for...

Homework Statement A main circuit contains six similar bulbs connected in series. One of the bulbs has a broken filament. Voltmeters X and Y of infinite resistance are placed in the circuit as shown. What are the voltmeter readings? A) X=0 Y=0 B) X=0 Y=240 C) X=40 Y=40 D) X=240 Y=0...

Homework Statement I have 3 data points of steady state temperature at 3 locations some distance away from a bulb, I need to calculate the temperature of the surface of the bulb. It would be best to assume the bulb is a hemispherical radiation source, based on the experiment set-up...

What produces the photons in light bulb filament? I know that electrons are emmitted by thermionic emmission from the filament . . . do they then fall back into the filament and emit EM radiation as they de-accellerate into the filament?

Does anyone know what it is, or where I can find the surface area of a typical 60W incandescent bulb filament? (if possible, by GE) I'm working on a research project and we're applying the stefan-boltzmann law. I'm calculating an area around 3e-5 m^2. I figure I'm in the ballpark, but I'd...