Question:
In a potentiometer experiment, the balancing length of a cell is $560\, cm$. When an external resistance of $10 \, \Omega$ is connected in parallel to the cell, the balancing length changes by $60 \,cm$.The internal resistance of a cell is
In a potentiometer experiment, the balancing length of a cell is $560\, cm$. When an external resistance of $10 \, \Omega$ is connected in parallel to the cell, the balancing length changes by $60 \,cm$.The internal resistance of a cell is
Updated On: Apr 15, 2024
- $1.4\, \Omega$
- $1.6\, \Omega$
- $0.12 \, \Omega$
- $1.2\, \Omega$
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The Correct Option is D
Solution and Explanation
Consider a cell ofe mf E and balancing length$l_1$
$E = kl_1$
The potential difference is balanced by length $l_2$.
$V = kl_2$
The internal resistance of the cell is given by
$r = \left(\frac{E-V}{V}\right)R =\left(\frac{E}{V } - 1\right)R = \left(\frac{l_{1}}{l_{2}} - 1\right)R $
$ = \left(\frac{560}{560 - 60} - 1 \right) 10 = \left(\frac{56}{50} - 1 \right)10 $
$ = \frac{6}{5} = 1.2 \Omega$
$E = kl_1$
The potential difference is balanced by length $l_2$.
$V = kl_2$
The internal resistance of the cell is given by
$r = \left(\frac{E-V}{V}\right)R =\left(\frac{E}{V } - 1\right)R = \left(\frac{l_{1}}{l_{2}} - 1\right)R $
$ = \left(\frac{560}{560 - 60} - 1 \right) 10 = \left(\frac{56}{50} - 1 \right)10 $
$ = \frac{6}{5} = 1.2 \Omega$
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Concepts Used:
Magnetic Field
The magnetic field is a field created by moving electric charges. It is a force field that exerts a force on materials such as iron when they are placed in its vicinity. Magnetic fields do not require a medium to propagate; they can even propagate in a vacuum. Magnetic field also referred to as a vector field, describes the magnetic influence on moving electric charges, magnetic materials, and electric currents.
A magnetic field can be presented in two ways.
- Magnetic Field Vector: The magnetic field is described mathematically as a vector field. This vector field can be plotted directly as a set of many vectors drawn on a grid. Each vector points in the direction that a compass would point and has length dependent on the strength of the magnetic force.
- Magnetic Field Lines: An alternative way to represent the information contained within a vector field is with the use of field lines. Here we dispense with the grid pattern and connect the vectors with smooth lines.
Properties of Magnetic Field Lines
- Magnetic field lines never cross each other
- The density of the field lines indicates the strength of the field
- Magnetic field lines always make closed-loops
- Magnetic field lines always emerge or start from the north pole and terminate at the south pole.