# What is Watt: Definition and 76 Discussions

The watt (symbol: W) is a unit of power or radiant flux. In the International System of Units (SI), it is defined as a derived unit of (in SI base units) 1 kg⋅m2⋅s−3 or, equivalently, 1 joule per second. It is used to quantify the rate of energy transfer. The watt is named after James Watt (1736-1819), an 18th-century Scottish inventor.

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1. ### Watt Rotational Speed Regulator's Lagrangian

I understand that it is a system with two degrees of freedom. And I chose as generalized coordinates the two angles shown in the pic I posted. I am having troubles in finding the kinetic energy of this system, cause the book tells me that the kinetic energy is something different then what I...
2. ### What factors determine wattage of electrons flowing through a wire?

Preface: I am new to physics and am trying to learn on my own, though I hope to take a class soon. I looked for a forum for beginners but didn't see one, but this seemed to be the closest forum. So I hope I can get some help with my question here. If it is the wrong forum, feel free to...
3. ### How can I convert that Watt peak rating to Megawatt?

Hello everyone. I need to calculate solar energy output (E) from a solar farm. The calculations are based on values from total module surface area in m² (A), panel efficiency (r), solar irradiance (GB) and losses (L) due to dust, cold temperature and ageing, which is estimated to be 0.75. Since...
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### Two 95 watt light bulbs walk into a bar ....

Two 95 W (120V) light bulbs are wired in series, then the combination is connected to a 120 V supply. How much power is dissipated by each bulb? Answer 24W I followed the explanations as such: r1 = 120^2/(95) = 151.8 R = 303 r2 = r1 W = 190 I = P/V I = 190/120 = 1.58 v1 = 190/1.58 = 60 p1 =...
5. ### Gigawatts and beyond solid-state Terahertz generators/oscillators

According to Vacuum Electronic High Power Terahertz Sources book by John H Booske, "In solid state electronic devices, the electron stream is a conduction (ohmic, collisional) current whereas in vacuum electronic devices (VEDs) the current is a convection (ballistic, collisionless) current...
6. ### Why this Simple Watt Meter for a 220 Volt Circuit works?

Hello guys! I'm just a begginer student. I found this circuit of a wattmeter that works only with resistors. Can someone explain to me how the 33k resistor give a voltage of 1 mV to 1 Watt? I did not understand why these resistor values has been chosen and why the it measures only in the 33k...
7. ### Why Isn't Horsepower an SI Unit, Despite Its Popularity?

When we talk about engines on automotive industry (cars, motorbikes, trucks, etc.), we often refer the power produced by such engines by horsepower. But when we talk about electricity, the power is measured in kilowatts. Despite the former case is highly popular, why isn't horsepower considered...
8. ### Convert solar radiation from Joule per cm square to Watt per meter^2?

I have solar radiation data in the units of Joule per cm^2 (joule per square centimeter) measured hourly. I want to use this data in evapotranspiratin calculation which requires radiation units as Watt per meter squared. How can I do this conversion?
9. ### Electrical Electric Hot Water Heater 2000 watt 220 volt run on 110 volt

Will a hot water heater element that is rated 220 volt AC by 2000 watts when only applying 110 volt AC just put out 1000 watt instead?
10. ### Conversion between Watt and Joule

example) E = 2734.2 joules per gram P = 2.73 x 109 watt/gram q: How can this conversion work? E = 21000 joules per gram P = ?
11. ### How to calculate the accurate capacity of a battery?

I'm trying to figure out how to calculate how much energy is stored in a battery between certain voltages. I know capacity is traditionally calculated by multiplying amps drawn by nominal voltage by time, but this seems like an approximation because voltage decreases as the battery is...
12. ### Calculating how many Joules are required to make a photon

A double covalent bond of nitrogen (N2) is 15.58eV Now let's go into a example. if i have a laser that is 477nm and i do 1240/477nm then i get 2.6eV per photon. Now if i do (15.58eV / 2.6eV) it equals ~6 photons. Now to figure out how many Joules are required for 1 photon I do (6.626*10^-34S *...
13. ### Brightness of bulbs depending on their watt level

Homework Statement Two 110-V light bulbs, one "25W" and the other "100W" are connected in series to a 110 V source. Then: a. the current in the 100W bulb is greater than in the 25W bulb b. the 25W bulb will be brighter c. the current in the 100W bulb is greater than that in the 25W bulb d. the...
14. ### 12 Volt 100 Watt Bulb V 120 Volt Bulb 100 Watt

Does a 12v bulb rated 100 watt give the same amount of light as a 120v bulb rated 100 watt?
15. ### Electrical Energy: 30-Day Output from Coal Plant

Homework Statement A power plant burns coal and generates an average of 700.0 Megawatts (MW) of electrical power while discharging 1162.00 MW as waste heat. Find the total electrical energy generated by the plant in a 30-day period. Homework Equations W = J/sec The Attempt at a Solution...
16. ### B Can a single nuclear bomb power the world for 2 trillion years?

Helly everyone. I'm new in physics and I don't understand many things there. What interests me the most is energy generation. I was mostly reading Wiki articles, and I found something I couldn't understand, so I'm asking for help. According to wiki, peak power output of the largest nuke ever was...
17. ### AC vs evaporative cooler: ratio of (BTUs/hr)/electric watts

Hi Air conditioner vs evaporative cooler: ratio of (BTUs/hr) / electrical watts I know evaporative coolers do not state BTUs/hr. I do not know why. Did anyone try them and record time taken to cool. I found this example, but I do not know if it is practically relevant...
18. ### Disagreements of preciseness of h in PDG and at Watt Balance

Planck constant in http://pdg.lbl.gov/2015/reviews/rpp2015-rev-phys-constants.pdf determined to 12 ppb. Planck constant in https://www.sciencedaily.com/releases/2016/06/160621115645.htm was measured with 34 ppb and it is a big step forward in replacing of Paris kilogram with more stable...
19. ### Combing Lasers To Create One Mega Laser

Hello, I am pretty new to physics but have a large amount of experience with Calculus and other sciences like chemistry. The theory I have come up with is that if I combine 6-8 5w laser beams together in a convex lens that can be moved forward or backward to change the focal point distance, I...
20. ### Battery life using 6000 watt inverter

I have four 125 ah batteries powering a 6000 watt inverter. The inverter is supposed to have a no load draw of 2 amps. I have a 12 amp 120volt Ac load. How long should I be able to operate before drawing my batteries to 50%
21. ### Best design for a 300 watt permanent magnet brushed DC motor

I have noticed there are a few designs for permanent magnet brushed DC motor, but I can't seem to find the benefits and downsides of either one. The first one (first attachment) uses three electromagnets placed on a triangular rotor. There are two arc permanent magnets on the outside. In this...
22. ### Do 40 Watt 1 Ohm resistors exist

My local hobby store says no. I want to draw a full 40 Amps from my power supply to play with a few formulas that give the magnetic field strength as a function of distance and current from a wire. The wire will be car battery cables. I have a calibrated Gauss meter for field measurements...
23. ### Effect (W) from Temperature

Let's say I have a cold bottle of water in a warm room (temperature is constant). Is it possible to calculate how long it will take for the water to reach a certain temperature? Do you guys know any formula for this? To be more general: What is the effect (W, J/s) that air in a certain...
24. ### B Understanding Watt & Newton: Questions for Physics Forum

Dear Physics Forum, I really don't understand the concept of watt and Newton. I have two questions, perhaps someone can explain it to me. ======================================================= Case 1: If a one Newton force is applied to a one kg rocket in space with no or very little effect of...
25. ### Two 700 watt blow heaters vs one 1500 watt heater?

I bought a small 1500 Watt portable blow heater for my room because it getting really cold, but whenever its turned on, it trips the circuit breaker.What exactly causes the circuit to break? I mean, what units should I concern myself with when buying a heater, --Watts or Voltage? Why does this...
26. ### 2000 watt sinewave inverter

am on final year project to build 2000watt puresinewave inverter using rf2110 driver to drive 4 irf740 in H-bridge with 2000watt constant voltage transfomer at the output of the h-bridge 4n28 or 4n35 to isolate SG3524 pwm from ir2110 with 12 v power supply i don't have a link yet on the...
27. ### OLED Watt, Ohms, and Volt Project

Hi, I am in fact quite new to these forums but have been lurking for a while. I am trying to design a OLED reader that will display the watts, ohms, and volts after being read from a circuit. Almost exactly like this: Any ideas on where to start? I am not necessarily a novice when it comes to...
28. ### I want to make a variable watt device

i was looking at an e-cig and wondering how it regulates watts. would it be viable to make your own? for those of you who don't know they run off of a 18650 3.7v battery that powers a coil. the coil is in the ballpark of .3 - 3.5 ohms. how do i get 30 watts of regulated power and jam it...
29. ### What is the watt rating of a mystery MOT transformer?

My apologies if this has already been covered. I did a search, but couldn't come up with anything. My question is this. If you come across a random transformer with no markings, how can you tell it's watt rating? I have acquired several MOT's, and wish to use them in a DC arc welder. I...
30. ### Determining truth of 555 watt amplifier board

Determining truth of "555 watt" amplifier board My math is showing that this amplifier is not 555watts but 140watts at 8 ohm at +-36v and 555 watts when shorting the output with ground. What do you guys think? amplifier board...
31. ### 10 Watt Solar To Car Battery With Diode

I have an 800 amp car battery no load connected at anytime to a 10 watt solar panel with just a regular diode in between after 4 or 5 hours in the sun terminal voltage reads 16 volts is this good? Would a battery connected this way last longer than one that sits idle uncharged for 6 months? John
32. ### Digital Watt Meter Connected To Microcontroller

Hello all, I am currently working on a project for a client in which my objective is to create an educational light bulb display. The purpose of this display is to demonstrate cost effectiveness between 4 different bulbs (incandescent, high-efficiency incandescent, CFC, and LED). Each...
33. ### Candela to Watt Conversion

I am working on rendering in Autocad and I have came across light. A point light representing a bulb has intensity measured in candela, default value 1500 Cd. I want to represent a normal bulb of 60 watts used for a room. Is there a way to calculate Candela to Watt? Can anyody help me on this...
34. ### Understanding Watt vs. Kilowatt-Hour: A Comprehensive Explanation

Hello, getting confused about watt vs watt.hour in the Watt's wiki page, an example is given on how to calculate wattage (power): So, (100kg x (9.81m/s2) x 3m) / 5s = 588 kg.m2/s3 this system needs aroud 600 watts of power to accomplish its task. ok. Then, lower in the page, an...
35. ### Calculating total price using kilo watt hours?

What is the cost for 1 hr? Current = 1 A Voltage = 25 000 V Kilowatt hour = £0.10 KWhr
36. ### How Does an Electric Current Supply More Energy to Higher Wattage Appliances?

Ok, I'm preparing to get shot down here because maybe this is a really dumb question but here we go... How does an electric current know to supply more energy (joules per second) to higher wattage appliances? For example: At home I can plug a 10W, 50W, 60W or 100W light bulb into a...
37. ### Calculating volume of plasma per watt, based on ionization energy

This is not homework, but I'm developing a new machine and doing my own research as a mechatronical engineer. I'm trying to calculate the maximum volume of Helium gas that can be ionized into plasma if I apply a power of 1 watt, where the voltage is 1000 volt and the current is 0,1mA. DATA...
38. ### Unlimited resistors to build a 5 watt circuit with resistance of 10 ohms.

Okay well my issue is from a basic problem. The problem is you are given an unlimited number of 10 Ohm resistors. They can only handle 1 watt of dissipation and you need to create a circuit that has a total resistance of 10 Ohms, and has a power dissipation of 5 Watts. They are actually looking...
39. ### Help Converting Lux to Watt

Hi! I need a little help. Here is my problem, I have a light source and a monocromator that separates the white light to to its components of different wavelenght. I want to measure the power of the output light which has a single wavelenght. I am using a Lux meter to measure the illumation of...
40. ### Watt (Power) better conceptually explained.

Here is the usual definition of Watt given by wikipedia: One Watt is rate at which work is done when an object's velocity is held constant at one meter per second against constant opposing force of one Newton. (or 1 N x m/s) Now I do NOT get this conceptually. So I like to imagine the...
41. ### How to power 375 watt 12vdc motor ?

Hi all. I am new to this great forum but have perused it many times past picking up some great knowledge. PROBLEM: ====== I have a rather heavy trailer dolly fitted with a 375 watt 12vdc motor (30amps?). I know I can mount a 12vdc battery to drive the unit but adding a battery would...
42. ### Joule Watt second = How many Plank?

I hope someone can help me find quantity of electricity. how big is a Planck? In other words, how many Plancks per one second (unit time) equal one Watt-second (unit energy) at 60 hz (377 radian)?
43. ### Wanted to designed a 5k Watt Wind Turbine

Hi everyone! I am new in physics forum and this is my first post. I need help from the people out there. I wanted to deisgn a Vertical Axis wind turbine to produce 5k Watt output with a frequecy of 50Hz, 220VAC, to completely run my home appliance 24 hours. Appliances include: -1.5ton...
44. ### Is it watt per second or watt per hour

Say I have a device (Thermoelectric generator) that "generates power" at 4 watts, as per watt meter reading, is it producing 4 watts a second or 4 watts an hour. I say it is producing 4 watts a second but my brother in law says 4 watts an hour so the watt meter can tell the future. Please bear...
45. ### 5000 watt 120V generator to charge 10 12V Automotive batteries

5000 watt 3600 rpm 120V generator to charge 10 12V Automotive batteries. Will this work? Less or more batteries? Im wanting to put together an electric car. If i use the items above (which is what I have laying around) What size motor would best for longevity, speed ? HP? RPM? AMPs?
46. ### Need ideas about a project : Thermodynamics description of a watt steam engine.

I have to do a paper ( kind of project ) for 4-6 page on Thermodynamics description of a watt steam engine. i have no idea where to start. It is for a Thermodynamics 1 class. Thanks in advance.
47. ### Uncovering the Mystery of a Zero Watt Bulb

greetings, what is the meaning of a zero watt bulb?how can be any bulb glow without any power consumption? thanks
48. ### How many joules are in a Mega Watt?

Homework Statement I know that you can't convert between the two because one is the rate at which energy is produced and another is an amount of energy. I need to find out how much energy was used for 417 billion kilowatt hours. This was the amount for a year. Is there a way to get it in...
49. ### 100 watt lightbulb resistor

I was with my electrician friend the other day, and we stuck two copper wires into each of the holes of a regular 120V outlet then smashed a 100W light bulb and took the resistor (small coiled looking thing) out of it and set it on a piece of wood and touched the copper wires to each end of the...
50. ### Unit convertion (lux - watt)

Hello frnds! Can anybody convert the following factors? V/(lx-s) to V/(um/cm2) at 555nm ?? Thank you.