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Confusion in sign convention of magnification?



The 2019 Stack Overflow Developer Survey Results Are In
Unicorn Meta Zoo #1: Why another podcast?
Announcing the arrival of Valued Associate #679: Cesar ManaraPoint me the primordial and intuitive concepts about this operations on physicsLorentz Transformation confusionshifting integration variable and taking derivative seemingly giving problemSolving for $theta$: $fracF - maw = Mcostheta + sintheta$Lens design using the matrix method (three lenses)Velocity-Time graph confusionFeynman Vertex Rule, Correlator, 2 diff coupling constants, why no-cross termsRay transfer matrixCan the same problem be done without calculus?Linear correlation between Distance and an Acceleration statistic










0












$begingroup$



A concave mirror forms a real image three times larger than the object on a screen. Object and screen are moved until the image becomes twice the size of object. If the shift of object is 6 cm. Find the focal length and initial position of object?




My attempt :-



1st way

As per question
$$m_i=3$$
$$Longrightarrow frac-f-f+u=3$$
$$Longrightarrow 2f=3u. ...(1)$$
For second case , On a similar way we get
$$ frac-f-f+(u+6)=3$$
$$ Longrightarrow f=2u+12. ....(2)$$
On solving equation 1 and 2 we get
$$f=-36 , u=-24$$



2nd way

Since the image is inverted the magnification must be negative.

So $$m_i =-3$$
$$Longrightarrow fracff-u=-3$$
For second case
$$fracff-(u+6)=-2$$
On solving we get
$$f=-36, u=-48$$



My question:- why I get two different answer, if use the sign. Convention in the formula of magnification I get different results when I use the sign. Convention in the value of magnification. Why this this happen and which is right process ?










share|cite|improve this question







New contributor




Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$
















    0












    $begingroup$



    A concave mirror forms a real image three times larger than the object on a screen. Object and screen are moved until the image becomes twice the size of object. If the shift of object is 6 cm. Find the focal length and initial position of object?




    My attempt :-



    1st way

    As per question
    $$m_i=3$$
    $$Longrightarrow frac-f-f+u=3$$
    $$Longrightarrow 2f=3u. ...(1)$$
    For second case , On a similar way we get
    $$ frac-f-f+(u+6)=3$$
    $$ Longrightarrow f=2u+12. ....(2)$$
    On solving equation 1 and 2 we get
    $$f=-36 , u=-24$$



    2nd way

    Since the image is inverted the magnification must be negative.

    So $$m_i =-3$$
    $$Longrightarrow fracff-u=-3$$
    For second case
    $$fracff-(u+6)=-2$$
    On solving we get
    $$f=-36, u=-48$$



    My question:- why I get two different answer, if use the sign. Convention in the formula of magnification I get different results when I use the sign. Convention in the value of magnification. Why this this happen and which is right process ?










    share|cite|improve this question







    New contributor




    Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.







    $endgroup$














      0












      0








      0





      $begingroup$



      A concave mirror forms a real image three times larger than the object on a screen. Object and screen are moved until the image becomes twice the size of object. If the shift of object is 6 cm. Find the focal length and initial position of object?




      My attempt :-



      1st way

      As per question
      $$m_i=3$$
      $$Longrightarrow frac-f-f+u=3$$
      $$Longrightarrow 2f=3u. ...(1)$$
      For second case , On a similar way we get
      $$ frac-f-f+(u+6)=3$$
      $$ Longrightarrow f=2u+12. ....(2)$$
      On solving equation 1 and 2 we get
      $$f=-36 , u=-24$$



      2nd way

      Since the image is inverted the magnification must be negative.

      So $$m_i =-3$$
      $$Longrightarrow fracff-u=-3$$
      For second case
      $$fracff-(u+6)=-2$$
      On solving we get
      $$f=-36, u=-48$$



      My question:- why I get two different answer, if use the sign. Convention in the formula of magnification I get different results when I use the sign. Convention in the value of magnification. Why this this happen and which is right process ?










      share|cite|improve this question







      New contributor




      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$





      A concave mirror forms a real image three times larger than the object on a screen. Object and screen are moved until the image becomes twice the size of object. If the shift of object is 6 cm. Find the focal length and initial position of object?




      My attempt :-



      1st way

      As per question
      $$m_i=3$$
      $$Longrightarrow frac-f-f+u=3$$
      $$Longrightarrow 2f=3u. ...(1)$$
      For second case , On a similar way we get
      $$ frac-f-f+(u+6)=3$$
      $$ Longrightarrow f=2u+12. ....(2)$$
      On solving equation 1 and 2 we get
      $$f=-36 , u=-24$$



      2nd way

      Since the image is inverted the magnification must be negative.

      So $$m_i =-3$$
      $$Longrightarrow fracff-u=-3$$
      For second case
      $$fracff-(u+6)=-2$$
      On solving we get
      $$f=-36, u=-48$$



      My question:- why I get two different answer, if use the sign. Convention in the formula of magnification I get different results when I use the sign. Convention in the value of magnification. Why this this happen and which is right process ?







      physics






      share|cite|improve this question







      New contributor




      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|cite|improve this question







      New contributor




      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|cite|improve this question




      share|cite|improve this question






      New contributor




      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      asked Apr 8 at 6:43









      Abhishek KumarAbhishek Kumar

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      New contributor




      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.





      New contributor





      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






      Abhishek Kumar is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.




















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