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Current Electricity — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsCurrent Electricity5 Marks
Question
  1.  
  1. State the principle on which a potentiometer works. How can a given potentiometer be made more sensitive?
  2. In the graph shown below for two potentiometers, state with reason which of the two potentiometers, A or B, is more sensitive.
  1. Two metallic wires, $P_1$ and $P_2$ of the same material and same length but different cross-sectional areas, $A_1$ and $A_2$​​​​​​​ are joined together and connected to a source of emf. Find the ratio of the drift velocities of free electrons in the two wires when they are connected (i) in series, and (ii) in parallel.
✓

Answer

  1.  
  1. The potential difference across any length of wire is directly proportional to the length provided current and area of cross section are constant i.e., ? ? = ?? where ? is the potential drop per unit length.
It can be made more sensitive by decreasing current in the main circuit/decreasing potential gradient/increasing resistance put in series with the potentiometer wire.
  1. Potentiometer B
Has smaller value of $\text{ }^V/_l$ (slope/potential gradient).
  1. In series, the current remains the same.

$I=neA_1V_{d1}=neA_2V_{d2}$
$\therefore\frac{V_{d1}}{V_{d2}}=\frac{A_2}{A_1}$
In parallel potential difference is same but currents are different.
$V=I_1R_1=neA_1V_{d1}\frac{\rho l}{A_1}=ne\rho V_{d1}l$
Similarly, $V=I_2R_2=ne\rho V_{d2}l$
$I_1R_1=I_2R_2$
$\therefore\frac{V_{d1}}{V_{d2}}=1$

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