Ohm's Law — Question 1

Question 1

Polarity reversal separates an ohmic slope from a voltage offset

At fixed temperature, a two-terminal specimen obeys $V=RI+V_{\mathrm{off}}$. Measurements give V=1.10 V at I=+.0200 A and V=-.900 V at I=-.0200 A.

1. Infer R and the offset voltage.

2. Predict V at zero current and explain whether the uncorrected terminal relation is strictly ohmic.

Question 1 - Solution

Polarity reversal separates an ohmic slope from a voltage offset

(a) Method and calculation

$$R=\frac{V_+-V_-}{I_+-I_-}=\frac{2.00}{.0400}=50.0\,\Omega.$$$$V_{\mathrm{off}}=\tfrac12(V_++V_-)=.100\,\mathrm V.$$

(b) Interpretation and further calculation

$$V(0)=.100\,\mathrm V,\quad V-V_{\mathrm{off}}=RI.$$$$V/I=R+V_{\mathrm{off}}/I\ne\text{constant}.$$Only the offset-corrected relation passes through the origin.

Physical check

A straight line alone is insufficient: proportionality requires zero intercept under the chosen terminal convention.