State Faraday’s law of electromagnetic induction.
A solenoid $S$ is wrapped around a soft-iron core, as shown in Fig. 9.1. A coil $C$ with 120 turns of wire is wound at one end of the core. The cross-sectional area of coil $C$ is $1.5\text{ cm}^2$. A Hall probe is positioned near the other end of the core. When the current in solenoid $S$ is steady, the flux density in the core is $0.19 \text{ T}$. The voltmeter attached to the Hall probe reads $0.20 \text{ V}$. The current in solenoid $S$ is then reversed at a constant rate in $0.13\ \text{s}$.
Calculate the reading on the voltmeter connected to coil $C$ while the current is changing.
Complete Fig. 9.2 with the voltmeter readings for the times before, during and after the current direction is reversed.