Answer the questions.[Phy-5M]

Question

State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.

Vidyadip · Accepted Answer

Firstly, Set up a circuit as shown in figure given below, consisting of a nichrome wire XY of length, say 0.5m, an ammeter, a voltmeter and four cells of 1.5V each. (Nichrome is an alloy of nickel,chromium, manganese, and iron metals.)

First use only one cell as the source in the circuit. Note the reading in the ammeterI,for the current and reading of the voltmeterVfor the potential difference across the nichrome wire XY in the circuit. Tabulate them in the Table given.
Next connect two cells in the circuit and note the respective readings of the ammeter and voltmeter for the values of current through the nichrome wire and potential difference across the nichrome wire.
Repeat the above steps using three cells and then four cells in the circuit separately.
Calculate the ratio of V to I for each pair of potential difference V and current I.

S.No.	Number of cells used in the circuit	Current through the nichrome wire, I (ampere)	Potential difference across the nichrome wire, V (Volt)	$\frac{\text{V}}{\text{I}}$$\Big(\frac{\text{Volt}}{\text{Ampere}}\Big)$
1.	1
2.	2
3.	3
4.	4

It is not obeyed when physical conditions of conductors like temperature keep on changing.
It is not obeyed by a lamp filament, junction diode, thermistor etc.
It is not obeyed in case of superconductors whose resistance is equal to zero.

Answer