A linear two-terminal network can be replaced by an equivalent circuit consisting of a current source in parallel with resistor RN , where RN is the ratio of
1. Closed circuit voltage to short circuit current at the terminal pair.
2. Open circuit voltage to open circuit current at the terminal pair.
3. Open circuit voltage to short circuit current at the terminal pair.
4. Closed circuit voltage to open circuit current at the terminal pair.
UGC NET - 2014,
Answer: C
Only statement 3 is correct. In Norton's theorem the equivalent resistance equals the open circuit voltage divided by the short circuit current at the terminal pair:
\[ R_{N} = \frac{V_{oc}}{I_{sc}} \]
Statements 1 and 4 begin with a "closed circuit voltage", which is not a defined quantity here. Statement 2 divides open circuit voltage by open circuit current, and the open circuit current is zero, so the ratio is meaningless. Hence only statement 3 holds.
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