विद्युतचुंबकत्व

According to Faraday's law of electromagnetic induction:

• The induced emf is equal to the time rate of change of magnetic flux ($d\Phi_B/dt$), not the total flux change ($\Delta\Phi_B$). Hence, statement 2 is incorrect.
• Statement 1 accurately states Faraday's law magnitude.
• Statement 3 is correct because $\mathcal{E} \propto N$.
• Statement 4 is a direct statement of Lenz's law.

In alternating current circuits:

• In a purely resistive circuit, current and voltage are in phase ($\phi = 0$).
• In a purely inductive circuit, voltage leads current by $\pi/2$ (or current lags voltage by $\pi/2$).
• In a purely capacitive circuit, current leads voltage by $\pi/2$ radians ($90^\circ$), described by $i = I_0 \sin(\omega t + \pi/2)$ for $v = V_0 \sin(\omega t)$.

The total magnetic flux linkage $\Phi$ through the secondary coil is directly proportional to the current $I$ in the primary coil:

Given values:

• Change in magnetic flux $\Delta \Phi = 15\,\text{Wb}$
• Change in current $\Delta I = 10\,\text{A} - 0\,\text{A} = 10\,\text{A}$

According to Lenz's Law, the induced current opposes the change in magnetic flux through the circuit:

• In figure (a): An irregular loop deforms into a circle. For a given perimeter, a circle encloses maximum area. Therefore, the area increases, causing inward magnetic flux ($\otimes$) to increase. To oppose this increase, the induced magnetic field must point outward ($\odot$), which corresponds to an anticlockwise current.
• In figure (b): A circular loop is deformed into a narrow straight wire. Its enclosed area decreases, causing outward magnetic flux ($\odot$) to decrease. To oppose this decrease, the induced magnetic field must reinforce the outward field ($\odot$), which also corresponds to an anticlockwise current.