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Question
Answer the following question.
Distinguish between Ohmic and non-ohmic substances; explain with the help of example.
Solution
| Ohmic substances | Non-ohmic substances |
| 1. Substances which obey ohm’s law are called ohmic substances | 1. Substances which do not obey ohm’s law are called non-ohmic substances. |
| 2. Potential difference (V) versus current (I) curve is a straight line. | 2. Potential difference (V) versus current (I) curve is not a straight line. |
| 3. Resistance of these substances is constant i.e. they follow linear I-V characteristic. | 3. Resistance of these substances is a function of V or I. |
| 4. Expression for resistance is, R = `"V"/"I"` | 4. Expression for resistance is, R = `lim_(Δ"l"→0)(Δ"V")/(Δ"I")="dV"/"dI"` |
| 5. Examples: Gold, silver, copper etc. | 5. Examples: Liquid electrolytes, vacuum tubes, junction diodes, thermistors etc. |
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