Physics
Physics
Problem
A student studies the behaviour of a nichrome wire by gradually increasing the potential difference across it at room temperature. She records the following readings: Potential difference V (V): 1.0, 2.0, 3.0, 4.0, 5.0 Current I (A): 0.10, 0.20, 0.28, 0.34, 0.38 Answer the following: a. (i) Draw a suitable graph using the above data, taking current along the vertical axis and potential difference along the horizontal axis. b. (ii) From the shape of the graph, identify the range of voltages, if any, over which the wire approximately obeys Ohm’s law. c. (iii) Explain physically why the graph ceases to be a straight line at higher voltages. d. (iv) How does the resistance of the wire change as the potential difference increases? Give reasons based on the graph.Intuitive explanation
This problem tests whether resistance is truly constant or whether it changes with temperature. As current flows through the nichrome wire, it heats up, and the wire's resistance increases—so Ohm's law () still holds at each moment, but the value itself isn't fixed. Calculate resistance at each voltage step using , then plot or analyze how grows with increasing current (and thus temperature), rather than assuming a single resistance value throughout.
Intuitive explanation
This problem tests whether resistance is truly constant or whether it changes with temperature. As current flows through the nichrome wire, it heats up, and the wire's resistance increases—so Ohm's law () still holds at each moment, but the value itself isn't fixed. Calculate resistance at each voltage step using , then plot or analyze how grows with increasing current (and thus temperature), rather than assuming a single resistance value throughout.