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CBSE - X - Physics

If R is a constant in ohm's law i.e.V=IR then why R doesn't have a fixed value.
{Extra=Like in case of Gravitational constant in F=(GMm)/r^2 , G has  value of 6.67×10^-11,then why R doen't have fixed value being a constant in proportionalty.

Asked by Ananay 30th March 2017, 8:19 PM
Answered by Expert


Hi Ananay!

That's a very good question!

Clearing your doubts on 'Resistance the constant':

  • The occurrence of Resistance in the Ohms Law explains that it is a mathematical consequence of direct proportionality being converted into equality and 'R' coming up as the coefficient of proportionality. This is how it is different from Gravitational constant which is actually a universal constant.
  • Now, in terms of resistance not having a fixed value, it should be noted that resistance does have a fixed value but for that particular wire or conductor only. Therefore, it can be concluded that resistance is constant for that particular wire but not a universal constant.
  • The value of resistance is fixed for a wire and it depends upon the length, cross-sectional area and the materialistic property straight rhoρ " /> (rho)    
Answered by Expert 31st March 2017, 5:35 PM

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