What is population: Definition and 277 Discussions

Population is the term typically used to refer to the number of people in a single area. Governments conduct a census to quantify the size of a resident population within a given jurisdiction. The term is also applied to animals, microorganisms, and plants, and has specific uses within such fields as ecology and genetics.

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  1. TheOfficialAB

    LASERs: Why is population inversion required for amplification?

    Hi, I'm doing a module on quantum optics and lasers. Most of the texts and online source I have read simply state that 'population inversion is essential for amplification in laser operation'. My question is, why? Amplification/Gain is essentially the result of stimulated emission. Can't...
  2. G.K. Masterson

    Writing: Input Wanted Nuclear Plants -- In the event of a 50% population collapse

    Hi all, I'm a science-fiction/fantasy writer who is in the midst of outlining a distant-future (10,000+ years) story. The main parts of it I can handle (humans on Earth have gone through a cycle of Intellectual --> Dark ages with the current era being a kind of pinnacle never again achieved)...
  3. rayne1

    MHB Finding initial population....

    Assume the population of bacteria in a culture increases at a rate proportional to the current population. The population increased by 2455 from t = 2 to t = 3 and by 4314 from t = 4 to t =5. Find the initial population and how many times does the population increase each unit of time? I don't...
  4. A

    Population proportion from a sample estimate

    I am interested to know which proper statistical test to use to know the population proportion from a sample taken from the population. For example, a sample of 20 people with 7 persons prefer the red color and 13 prefer the blue color. Which of the following methods should be used to conclude...
  5. S

    MHB Class Project: Comparing 2 Population Means & Std Devs

    For our class project we are to collect some data from two populations, summarize it in table and graphical form, and conduct at least two different hypothesis tests that use different procedures and construct two different confidence intervals. I wanted to summarize my plan here and ask for...
  6. Christo

    Population Growth Equation

    1. The population of a certain country grows according to the formula: N = N0e^kt Where N is the number of people (in millions) after t years, N0 is the initial number of people (in millions) and k = 1/20 ln 5/4. Calculate the doubling time of this population. Leave your answer in terms of ln...
  7. K

    Population Dynamics: Logistic Model (Differential Equations)

    Homework Statement Population Dynamics: Logistic model. Suppose the environmental carrying capacity of the population is 100000 and the growth rate a t=0 is 5%. . If the population starts at 10000, how long does it take for the population to reach half the carrying capacity? dp/dt = A P...
  8. N

    Population growth problem

    1. The Problem In the mythical country of Myland, the population recently reached 10 million. At that time, a popular news magazine predicted that with an average yearly growth rate of 2%, the population would be 20 million in 50 years. How does this value (18 million) compare to the value...
  9. G

    Calculating electron and hole population in a semiconductor

    I'm very new to semiconductors. I want to do basic calculations. How would I go about calculating and graphing the energy of the electrons and holes given the magnetic field and the state. Also, how would I do the same for the electron and hole population.
  10. DiracPool

    Explore Weird Population Distrib. of China, India, USA, Russia, Canada

    I saw on the news that Obama was going to visit Beijing pretty soon, and got to thinking...why does China have so many more people than the USA, when ostensibly, as the worlds melting pot, we should be the "Times square" of the planet and attract the greatest volume of planetary (even galactic)...
  11. W

    Probability of Sample Proportion Within 0.05 of Population

    Homework Statement Person A claims that the porportion of household installed with solar heater is 0.15. A random sample of 250 household iataken. Assuming the claim of person A is true, finding the probability that tge sample proportion is within 0.05 of the population proportion. Homework...
  12. G

    What is the Significance of Testing Population Variance in a Sample?

    Homework Statement Given that 8 person vote for Mr Tan , i can't understand why the probability is sum of 0 people vote for him until 8 people vote for him. Why not the probability = 22c8 ( (0.6)^8 )( (0.4)^14) ? Homework EquationsThe Attempt at a Solution
  13. wolram

    Help Control the Rooligator Population: Take Part in the WLC Survey

    The rooligator is a voracious pest, a ( flood ) of them have been known to strip a field of oil seed rape in a single day. The rooligator is so named because of it's elongated jaw and gnawing teeth, they are the size of a large rat and can move very rapidly, science is trying to find a way to...
  14. M

    Solving a Population Growth Problem

    Ok so this is homework question, i know it is supposed to be here but the math question would not go in any homewrok category i need help and my parents do not even know how to solve it. Math question: The population of Heidi's hometown is 18,079 people in 2006. In 2007 it was 19,087...
  15. I

    MHB Population Growth: US Carrying Capacity & Predictions

    i suck at these kind of problems #1 Suppose a population grows according to a logistic model with initial population 1000 and carrying capacity 10000. if the population grows to 2500 after one year, what will the population be after another three years.#2 a. make a guess as to the carrying...
  16. I

    MHB Integration and population dynamics?

    can someone explain this problem step by step (not a homework problem, just an example i found and i want to see how its done). a hot wet summer is causing a mosquito population explosion in a lake resort area. the number of mosquitoes is increasing at an estimated rate of 2200+10e^(0.8t) per...
  17. A

    Life tables in population ecology

    Homework Statement http://imgur.com/OInF6O2 The blue table shows the mortality and offspring production rates per year per age class by individuals of an unnamed species. The orange tables shows the starting population at time t, I have to find the number of individuals at T+1 (next year)...
  18. U

    Modelling of population of neurons

    I am a bit confused between single neuron models and population of neuron models. If we have single neuron models (Integrate and fire model etc) then why we want to develop models for population of neurons? Although single neuron models are ordinary differential equations (easy to analyze) and...
  19. A

    Population Inversion: Pumping Wavelength for 3.5 eV Energy Difference

    Homework Statement In order to achieve population inversion between two states that are separated by an energy difference of 3.5 eV, what wavelength of pumping should be used. Homework Equations Not sure. The Attempt at a Solution I have no idea where to start with this one...
  20. E

    MHB In which year does the population reach 2000 people?

    So, this looks really simple, but I keep getting a different answer from the textbook. Could someone help? Thanks 3d) The growth in population of a small town since 1996 is given by the function P(n) = 1250(1.03)^n In which year does the population reach 2000 people?
  21. X

    Modeling of a Single Species Population (F.O. D.F.Q.)

    First off, this is a typed paper project, and I am not asking for anyone to solve my work or to give me the answers. Just please point me in the right direction or help me through any parts I am not understanding. This is also a 7 part project, and I would like help on this first problem to get...
  22. D

    Shifting integration variable when determing population densities

    Hi, I'm hoping someone can enlighten me on this as I'm a little bit fuzzy on the reasoning: Say I have a space-time dependent field B_{a} that interacts with fermions such that it affects their energy dispersion. It appears in the energies in the form...
  23. paulmdrdo

    MHB Differential equation population growth problem

    A bacterial population B is known to have a rate of growth proportional to B itself. If between noon and 2pm the population triples, at what time no controls being exerted, should B becomes 100 times? what it was at noon? using this formula $\displaystyle P(t) \;=\;P_oe^{kt}$ please help me...
  24. T

    MHB Calculating Power for a Study: Population µ = 100, σ = 20

    I have had some issues with an equation in one of my classes, hoping some one can point out what I am going wrong. If anyone can point out some flaw in my process or calculations I would appreciate it. The problem lists: Population µ = 100, σ = 20. Planning to have a sample of 50...
  25. C

    Rodent Population as a differential equation.

    Homework Statement https://www.physicsforums.com/attachment.php?attachmentid=65556&stc=1&d=1389570667 For those who can not see the screen shot here is the question... Suppose the population P of rodents satisfies the diff eq dP/dt = kP^2. Initially there are P(0) = 2 rodents, and their number...
  26. N

    MHB Sample & Population Variance & SD Review

    Reviewing for finals when given a sample of a 8 values {1,2,3,4,5,6,7,8} , when solving for the SD and the variance do I solve for the population variance and SD OR since the question states that it is a sample you solve for the sample SD and variance
  27. preston8

    Creating formula from musical bar test population

    Hello, I'm creating a musical device which has stainless steel bars cut with a laser cutter. They are all the same length but vary in width. I created a set of test lengths (50 in total) and tested the pitch of each one using a tone analyzer. Now I'm looking to fit a curve to the data so...
  28. alane1994

    MHB Population Dynamics.... again

    Hey MHB, I have this rather large and convoluted project that consists of two problems. I have finished the first problem that consisted of 4 parts. I am working through the second part right now. It has a preamble that is kinda important. I will post that as well as the problems that I am...
  29. K

    Two Level System with thermal population

    Hello, the task is the following: Consider a two-level system with thermal population. a) Show that the rate equation for the state N_2 is the following: \frac{dN_2}{dt}=w(N_1-N_2)-\frac{N_2-N_2^e}{\tau} w=B_{12}\rho({\nu}) \,\,\, N_2=N_2^p+N_2^e\,\,\, N_1=N-N_2 N_2^p is the portion of...
  30. J

    Modeling Population Dynamics of Flies, Frogs, and Crocodiles

    Homework Statement Flies, frogs, and crocodiles coexist in an environment. To survive, frogs need to eat flies and crocodiles need to eat frogs. In the absence of frogs, the fly population will grow exponentially and the crocodile population will decay exponentially. In the absence of...
  31. MarkFL

    MHB Answer αℓєєиα♥'s Logistic Population Growth Model Q on Yahoo! Answers

    αℓєєиα♥'s question at Yahoo! Answers regarding the logistic population growth model Here is the question: I have posted a link there to this topic so the OP can see my work.
  32. N

    World population question that I'm contemplating

    The most recent world population doubling has occurred in about 40 years. Suppose that the next doubling also occurs in 40 years, but that agricultural progress also manages to double food production. Then how many people will be starving 40 years from now, as compared to the numbers...
  33. alane1994

    MHB Population Dynamics: Solving Differential Equations for (a), (b), and (c)

    Suppose that the population of a species of fish in a certain lake is hypothesized to grow according to a logistic model of population growth with growth rate \(r=0.3\) and carrying capacity \(k=3000\). Assume initially there are 2500 fish of the species in the lake. Determine the correct...
  34. T

    Population Model Homework: Determine Equilibrium Solutions

    Homework Statement The simplest useful model for fisher comes from the logistic model for population growth, together with a harvest h which is proportional to the current population P, that is, h=EP, where the constant E is called the effort. E measures the fraction of the population...
  35. E

    How do you estimate the sample size of a population given that there i

    i need the formulas and the steps i know how to use the confidence interval equation after that it gets dark $$\frac{N*Var(x)}{(N-1)B^{2}/k^{2} + Var(x)}$$ break down the above equations into many steps and formulas
  36. J

    How Likely For Trait to be Preserved Across Large Population?

    I'm trying to understand the impact of gene clustering on genetic inheritance, and to get an overall sense of what the state of knowledge is in this area (i.e., how much is currently unknown?) By way of example, say an original group of geographically isolated people we now call "Spanish" had...
  37. A

    Computing Average Age of Mothers in Age-Structured Population

    Hi, I have the following problem. Consider an age-structured population growing according to a Leslie matrix. Suppose the population is in stable exponential growth, i.e. its age-structure is constant in time, while the total population is exponentially growing (or decreasing) with exponent...
  38. N

    Mean and SD of the inverse of a population

    If one has the mean and standard deviation of a population, is it possible to calculate (or estimate) the mean and standard deviation of the inverse population (ie. 1/(every value in the original population)? Thank you!
  39. N

    Modeling Population Growth [dP/dt = k P - A P2 - h]

    Does anyone know how to solve dP/dt = k P - A P2 - h for P. I understand partial fractions are needed and I have already solved dP/dt = k P - A P2. Is anyone able to solve it, Cheers NZBRU.
  40. D

    Optimizing Response Rates: Statistical Analysis for Small Population Sizes

    Sorry I need help in a hurry. This is for work and I haven't done this in a long time. I have a population of ~ 5,338,000 And I know 0.74% respond to something. I want to know if a population of only 5,000 will respond better or worse than my 5 million. I am worried that it is too...
  41. M

    Calculus problem about population count

    Homework Statement Calculus question about tag and recapture? Here is the problem, i tried to do most of it but don't understand what its asking on c and d. Tag and recapture is used to estimate populations of animals in the wild. First, sample of animals are captured, number=n. They are...
  42. B

    Tissue Engineering Problem - Find minimum starting cell population

    Homework Statement You want to create a tissue engineered blood vessel using smooth muscle cells. Your plan is to isolate smooth muscle cells from discarded human tissue obtained from heart surgery and grow them for a long time to create cells own ECM. Smooth muscle cells have enormous...
  43. J

    Population Dynamics how to solve a particular ODE

    Homework Statement I have a population problem where: \frac{dy}{dt} = ay - by^{2}-\frac{c*y^{3}}{d+y^{3}} I need to find an expression for y(t). I'm not looking for the answer, just some advice/ helpful hints. Thank you. Homework Equations The Attempt at a Solution I...
  44. T

    Relative population density of stars and galaxies

    Homework Statement The number of stars around the Sun, within a distance of 17 ly, is 75. The number of galaxies in the local group, within a distance of 4.0 x106 ly from the Sun, is 26. Calculate the average popluation density, per ly3, of stars and galaxies. Homework EquationsThe Attempt...
  45. A

    Log-normal distribution of an exponentially growing population

    Homework Statement Consider an exponentially growing bacterial population in a fluctuating environment. The bacterial population can be modeled as a multiplicative random walk, starting at x = x0. x evolves in time according to the following rules x(t + 1) = x(t)*(1 + ε): probability...
  46. nomadreid

    Sample and population variances: elementary question

    Given a sample of a normally distributed population, then the sample variance ≈the population variance divided by the sample size. Nice. However, if one now increases the sample size to the population, this becomes that the population variance ≈ the population variance divided by the population...
  47. R

    Maple Two Species Population Model

    The academics and the technicians of a university faculty are planning a paintball battle and the mathematicians are trying to predict their chances of winning with a continuous model. They are representing the numbers in the two teams at any time t as and respectively and have decided that the...
  48. C

    Probability question: testing whether a population is 50/50

    Say I have a "large" population (larger than 1000) of red cards and blue cards which I want to find if it is evenly split (1:1 red:blue ratio). So I do an experiment and pull out 125 cards at random, and find that I have 50 red and 75 blue. Based on this experiment, what can I say about the...
  49. R

    Two Species Population Models

    The academics and the technicians of a university faculty are planning a paintball battle and the mathematicians are trying to predict their chances of winning with a continuous model. They are representing the numbers in the two teams at any time t as and respectively and have decided that the...
  50. B

    Maximum population for 2000 Kcal per day

    Dear physics, I'm new to the site. I found it reading this topic: https://www.physicsforums.com/showthread.php?t=145043 I wonder if we could manage to answer, if some not critical precision, the question of: How many people can live confortably, eating only potatos, in earth? As of...
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