What is Meter: Definition and 309 Discussions

The metre (Commonwealth spelling) or meter (American spelling; see spelling differences) (from the French unit mètre, from the Greek noun μέτρον, "measure", and cognate with Sanskrit mita, meaning "measured") is the base unit of length in the International System of Units (SI). The SI unit symbol is m.
The metre is currently defined as the length of the path travelled by light in a vacuum in 1/299 792 458 of a second.
The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's circumference is approximately 40000 km. In 1799, the metre was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. The current definition was adopted in 1983 and modified slightly in 2002 to clarify that the metre is a measure of proper length.

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  1. Kekkuli

    I Isn't the speed of light tautologically 299792458 m/s?

    A meter is defined as the distance that light travels in 1/299792458 of a second, so the speed of light is obviously always 299792458 m/s.
  2. neilparker62

    Insights The Poor Man’s Milli-Ohm Meter

    [url="https://www.physicsforums.com/insights/the-poor-mans-milli-ohm-meter/"]Continue reading...
  3. P

    I Measuring Low Resistance: Why Meter Bridge is the Preferred Choice

    Why meter bridge is chosen over post office box to measure low resistance?
  4. N

    Earth ground meter Vs Multimeter

    Dear forum please help me with the following understanding: There is (are) such equipment Earth ground testers (https://www.fluke.com/en/products/electrical-testi...) - it is used to measure grounded electrical systems or to measure. Such equipment is having multiple poles that are attached to...
  5. Steven Ellet

    Understanding and Interpreting Data from Static Electricity Meter Experiments

    My static electricity meter won’t stay zero when I am not moving and when I am electrically grounded. Video: EDIT: Can you see this? shorturl.at/jsGV0
  6. G

    Derive the Venturi Meter eqn from the Bernoulli eqn

    Advanced apologies for this format; I am posting my question as an the image b/c the Latex is being very buggy with me, and I lost a kind of lengthy post to it. Can anyone show me what I am doing wrong? I have attached a pdf version for easier reading if need be.
  7. T

    I Permittivity/Permeability, the speed of light, and the meter

    Good evening all, I had a question on how the standard for the meter is defined. A simple Google search tells us that since 1983, the meter has been internationally defined as the length of the path traveled by light in vacuum during a time interval of 1 / 299, 792, 458 of a second. Many other...
  8. Shreya

    Voltage Null Points of a Mechanical Meter Bridge

    My reasoning is that the wire has a resistance/unit length. The resistance of AD must equal that of AB for D to be called a null point. If we move jockey to the left, the resistance of AD decreases, thereby decreasing the potential drop across it. This means that the V of D is more than that of...
  9. M3D1

    B How is 1N enough to move a 0.1kg apple 1 meter high?

    Example: How much energy is needed to lift an 0.1 kg apple up 1 meter? To hold a 0.1 kg apple against gravity needs 1 Newton of force: F = mg F = 0.1 kg × 9.8 m/s2 F ≈ 1 N But holding an apple is not work, the apple needs to move! So, raising it using 1 N for 1 m (both in same direction!)...
  10. S

    Calculating distance between lux meter and light source

    I am currently performing some experiments to calculate the distance between a light source and a lux meter where the light source points directly towards the lux meter. Is it possible to calculate the exact distance between the light source and the lux meter given that we have a lux value...
  11. amizy9990

    A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire

    A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire. What speed do the electrons move when there is 2 A current in the wire. t=q/t=3,20*10^3 C/ 2.0 A = 1,5*10^22 s v= 1m/1,5*10^3s= 6,6*10^-4 m/s
  12. Fikremariam

    Electric Field -- Potential between the ends of a 2 meter stick

    I tried to find the charge from the formula v=k q/r and apply it to find the field but couldn't be sure
  13. tolerl

    Best CT connected energy meter rating for a CT with secondary 5A

    I work in a Maldivian Utility Company. Our engineering team is pretty weak so I don't have anybody in the company to ask even though this is the state electric company. A supplier quoted us 2 CT meters . Rating for one is given as 1A(6A) and other as 5A(20A) which I believe is 1A basic current...
  14. M

    Doubt about "venturi meter" question

    fig equations that I used: Δz = 0 = and I got the following result (which is the same in the book's solution book): but in my test I can only choose one of these: I would like to know if there is a mistake by my teacher or if it is possible to obtain one of these multiple choice...
  15. Teeg

    Volumetric Flow Rate through a Venturi Meter

    Hi, I have designed a simple Venturi meter to measure pressure differential across to section of the pipe as pictured. However in calculations I am not sure if I am doing something wrong. I am trying to calculate Volumetric flow rate in L/s. I am using Bernoulli Equation of the Venturi meter as...
  16. henriquevpp

    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...
  17. A

    Calibration of a Meter Stick

    I'm trying to find literature on different methods to calibrate a meter stick. Does anyone know any good sources I could use?
  18. Libensek

    How can I make a Heat Flow Meter?

    I tried to created it but i dknt know how to even start
  19. andacbaba123

    Meter Stick Lab Systematic Error

    Hello everyone! In class, we made a lab. The lab was basically first measuring a mass. Then, we found a meter stick's center of mass by finding the point where the stick was balanced. After that, we hanged the mass and changed the fulcrum point. We balanced it again and the torque equation gave...
  20. H

    What voltage/current/power meter do you use in your (hobby) projects?

    Hi! I am looking for some volt, amp, watt meter ideas. If I google "ac peak voltage for 230v" then it says: "The UK mains supply is 230V AC, this means 230V RMS so the peak voltage of the mains is about 320V". Does this mean that voltmeter that is rated for 80-300V AC will burn down when...
  21. A

    Harmonic motion of four meter sticks

    inertia of center = [(1/12) m*L^2 + m(L/2)^2]*4 inertia of center = (4m*L^2)/ 3 inertia around pin = (4m*L^2)/ 3 + 4m(L/ 2^(1/2) )^2 inertia around pin = (10m*L^2)/ 3 inertia around pin = (10*0.1*1^2)/ 3 = 0.33 kg*m^2 d= 1/2^(1/2) = 0.707m (m*g*d/inertia)^1/2 = 2pi/period...
  22. mfb

    B Thirty Meter Telescope can resume construction

    Larger telescopes collect more light and, thanks to modern adaptive optics, achieve a better resolution. After several telescopes with ~10 m diameter three projects aim at much larger telescopes:Giant Magellan Telescope (GMT), Chile, 24.5 m diameter, 368 m2 area Thirty Meter Telescope (TMT)...
  23. P

    A When and Why Was the Definition of the Meter Changed?

    The wording of the definition of the meter has apparently changed recently. I'm wondering about the motivation for the change. The current definition is: The older definition (1983, I think) was Does anyone know when and why the change was made?
  24. S

    With what speed does the tip of a 25 meter high tree hit the ground?

    Hi, I am still working on the same exams problems, the second last one is giving me a bit of a headache after I found this https://physics.stackexchange.com/questions/2372/how-long-would-it-take-for-an-upright-rigid-body-to-fall-to-the-ground which contradicts my solution. Can I assume that when...
  25. D

    Electrical How to build a DIY laser power meter

    How do I build diy laser power meter. I tried shining 5 milliwatt laser on photodiode. Photodiode is connected to led. Led never turned on.
  26. babaliaris

    I How was the speed of light calculated before the redefinition of the meter?

    I'm reading a book from the authors Halliday and Resnick and it says that The meter is the length of the path traveled by light in a vacuum during a time interval of 1/299 792 458 of a second. This time interval was chosen so that the speed of light c is exactly c = 299 792 458 m/s. I...
  27. DJ_Juggernaut

    I On The Length of a Meter Stick

    Can a single meter stick be one meter per A and less than a meter per B? If so, isn't this is a simple paradox? Does anyone here see it that way?
  28. O

    Is My Light Meter Reading in mLux or Lux?

    Hi, I'm studying physics and was wondering about the light meter I used. It was set to 2000 so I could get readings, instead of 2 because the readings wouldn't show. Does this mean my values I get from the light meter is in mLux (milli) or just Lux?
  29. M

    Trying to buy quality EM meter and

    Hi all! Not sure if this is the right place but I am having really hard time getting these questions answered in other places as well. I became interested in EM topic when power company decided to build a 2x110kV power line near my house. I would like to approach this problem rationally with...
  30. wirefree

    Can a microwave VSWR meter be used to measure Power?

    G'day. Recently we conducted an experiment in the microwave engineering lab where we were tasked to measure power in, what's called, a Directional Coupler. Here you'll find much on it. My concern with the setup is that we took our measurements on a VSWR meter by noting off the db scale. So...
  31. S

    Finding mass of unbalanced meter stick from torque

    Homework Statement Unbalanced meter stick has hanging mass of 100g at 0m point. I then moved fulcrum to balance it and it was balanced at the 0.33m point. (The hanging mass and 0m point is on left side) I want to get the mass of the portion of the meter stick on right side, but I am confused as...
  32. J

    Air Turbine Design -- advice regarding a Hall sensor type air flow meter

    Hello all, I am after some advice regarding a hall sensor type air flow meter. I know from experience that most hall sensor flow meters allow a bypass of fluid around the turbine/fan. However I would like to know what would happen if this was the case of the design below. Specifications...
  33. J

    Design a Handheld Electric Field Meter with Arduino

    Hello, I want to create a handheld electric field meter to measure the strength at a certain point with an arduino. I have seen various ideas online but I am still not sure what kind of design to use. Is the right concept to use two antennas. Measure the voltage on each and then calculate the...
  34. R

    What is this LED for in this Electricity Meter?

    Hello What is this led for in electricity meter
  35. Mzzed

    RF Power Meter / SWR Meter Equivalent Circuit

    I'm starting to get into RF electronics, and an upcoming project involves the use of a power meter / SWR meter. How do we model a power meter in terms of an equivalent circuit? i.e. is it just another impedance? or a transformer? or does it not effect the circuit at all, so we just don't include...
  36. thee qs

    Ampere definition and infinite wires separated by 1 meter

    Homework Statement 3 - 2 , 1 km wires ( so acting like infinite wires ) , both have same current , no direction specified , , separated by 1 meter distance and having between them a magnetic force of module 0.02 N . find the current i= Homework Equationsthe definition of 1 ampere has same...
  37. Chronos

    Stargazing What makes the Thirty Meter Telescope a game-changer for astronomy?

    This paper; https://arxiv.org/abs/1806.02481, The Thirty Meter Telescope International Observatory facilitating transformative astrophysical science, provides an update on plans for the thirty meter telescope. This monstrosity is to be built next door to the Keck in Hawaii and is slated for...
  38. S

    Plumbing How can I make a 1-10 liter/hr flow meter?

    I'm working with tap water. I'm building a fertilizer injection system, and need to control the rate that water flows through the bypass, through the fert tank, and back into the main line. At small flow values, reynolds numbers are on the non-flat part of the curve, so making something that...
  39. Hiero

    I Meter stick slides over a meter wide hole at a high speed

    Consider a meter stick sliding along its length towards a hole which is a meter wide in the direction of motion. Suppose the meter stick moves with speed so that the gamma factor is 10. Then in the stick’s frame, the hole is 10cm and should be easy to cross. But in the hole’s frame, the stick...
  40. P

    Moment of inertia of a meter stick

    Homework Statement A meter stick has a mass of 0.2kg. A small hole is bored in it at the 10cm mark so the meter stick can be hung from a horizontal nail. The moment of inertia of the meter stick around an axis at the 10cm mark is Homework Equations m = 0.2kg I = mr^2 The Attempt at a...
  41. S

    Angled falling Meter Stick on a frictionless surface

    Homework Statement A meter stick is held 60 degrees to the horizontal on a flat frictionless surface. If it is let go what is the distance the back the stick will reach with respect to the length of the meter stick (l). Homework Equations I = 1/3 mL^2 Don't know what to use. This seems more...
  42. E

    Calculating Mass of a Balanced Beam with Two People Using Torque Equations

    Homework Statement Determine the mass of a 4.5 meter beam, if it is balanced on a fulcrum 2.04 meters from the left end. A 886 N man stands on the very left end, and a 393 N girl stands on the right end. [/B]Homework Equations T = Fr The Attempt at a Solution The torque applied by the man...
  43. K

    Finding the Mass of a Meter Stick (Torque and Balance)

    Homework Statement Attach a 216.82 g mass at the 90 cm position. Red-adjust the position of the knife edge such that the meter stick is once again balanced. Determine the mass of the meter stick without using the balance. 2. Homework Equations Torque = force * distance from center F=ma T1+T2...
  44. C

    Understanding Backpressure Effects on Flow Meter Calibration

    Hello all, I have an in-house designed flow meter with roughly the configuration in the figure. In the setup, a restriction is placed in the flow stream (the rows of horizontal lines in the figure). Pressure measurements upstream and downstream of the restriction, P1 and P2, respectively are...
  45. R

    Data logger for static charge meter

    Hello, I have just bought the static charge meter, Keyence SK-1000. Analog output is sent through two small cables denoted as: 1. Analog output (surface potential). 2. Analog output GND. The analog output can be set to one of the following values: NONE (OFF), -5 to +5V, 0V to 5V, 1V to 5V, 4mA...
  46. Garlic

    Best pH Meter to Buy: 20-40 Bucks

    Hello everyone, In a few weeks I am going to have my anorganic chemistry laboratory experiments, and I want to buy one PH-Meter. I'm looking for a model that is realible but not expensive (in the order of 20-40 bucks) I'll be happy to hear your suggestions Thanks :smile:
  47. E

    Energy needed to jump one meter

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > So I know the formula of kinetic energy (mv^2 divided by 2). And I have a mass of 50 kg and a speed of 1 m/s will that mean I online need 25 Joules to make that jump?
  48. T

    AC Mains meter circuit design for energy sources....

    What circuit design is used to ensure that the renewable energy source does not begin to absorb energy from the grid (for instance, when its terminal voltage drops below the distribution line voltage)?
  49. dlgoff

    Meter Movement Magnet Activity: 600-800 CPM

    The other day I used my Ludlum survey meter to check out if any of my old junk electrical part may show any traces of radioactivity. I was rather surprised to find an old meter movement magnet showed some activity. Today I took some pictures while determining just how much activity there was...