What is potential gradient along the wire

Reading of voltmeter


Asked by diyasinha1701 | 31st Jul, 2021, 09:58: AM

Expert Answer:

Let k be potential gradient , i.e., voltage per unit length of potentiometer.
Initially with 2V cell alone Null point is obtained at a length 500 cm
Hence we have ,  2 V = k × 500    or     k = 4 × 10-3 V/cm
After connecting Voltmeter across cell , null point becomes 490 cm .
This is because voltmeter draws small amount of current and acts as high resistance is connected across cell .
Hence , terminal voltage V of cell is given as ,   V = k × 490 = 4 × 10-3 × 490  = 1.96 Volt
Since voltmeter reads terminal voltage , voltmeter reading is 1.96 V
Instead of cell , only voltmeter is connected between one end of potentiometer wire and jack,
we get voltage drop beween potentiometer wire end and jack.
When jack is sliding along the potentiometer wire we get a linear graph of Voltage Vs wire length as shown below. 
Slope of graph is potential gradient , i.e., voltage per unit legth of potentiometer wire 

Answered by Thiyagarajan K | 31st Jul, 2021, 03:22: PM