NEET Physics: Electromagnetic Induction and Alternating Currents questions with solutions

Q1. In hydrogen atom, an electron is revolving in the orbit of radius \( 0.53 \dot{A} \) with \( 6.6 \times 10^{15} \) radiation/s. Magnetic field produced at the centre of the orbit is

1. \( 0.125 W b / m^{2} \)
2. \( 1.25 W b / m^{2} \)
3. \( 12.5 W b / m^{2} \)
4. \( 125 W b / m^{2} \)

Answer: \( 1.25 W b / m^{2} \)

An electron moving in a circular orbit constitutes a current loop with current I = e f. The magnetic field at the center of a single circular loop is B = μ0 I / (2r), which gives the stated value when the given radius and frequency are substituted.

Q2. A parallel plate capacitor is charged and then the battery is disconnected, When the plates of the capacitor are brought closer, then This question has multiple correct options

1. energy stored in the capacitor decreases
2. the potential difference between the plates decreases
3. the capacitance increases
4. the electric field between the plates decreases

Answer: the capacitance increases

For a parallel-plate capacitor, capacitance is inversely proportional to plate separation, so bringing the plates closer increases capacitance. Since the battery is disconnected, the charge remains constant, which also means the potential difference and stored energy change accordingly.