Conceptual Questions - Chapter 4 Electromagnetic Induction and Alternating Current 12th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated On May 15, 2024

By SaraNextGen

Conceptual Questions
Question 1.
A graph between the magnitude of the magnetic flux linked with a closed loop and time is given in the figure. Arrange the regions of the graph in ascending order of the magnitude of induced emf in the loop.
Answer:
According to electromagnetic induction, induced emf,

Ascending order of induced emf from the graphical representation is $\mathrm{b}<\mathrm{c}<\mathrm{d}<\mathrm{a}$.
Question 2.
Using Lenz's law, predict the direction of induced current in conducting rings 1 and 2 when current in
the wire is steadily decreasing.
Answer:

According to Lenz's law, a current will be induced in the coil which will produce a flux in the opposite direction.

If the current decreases in the wire, the induced current flows in ring 1 in clockwise direction, the induced current flows in ring 2 in anti-clockwise direction.
Question 3.
A flexible metallic loop abed in the shape of a square is kept in a magnetic field with its plane perpendicular to the field. The magnetic field is directed into the paper normally. Find the direction of the induced current when the square loop is crushed into an irregular shape as shown in the figure.
Answer:

The magnetic flux linked with the wire decreases due to decrease in area of the loop. The induced emf will cause current to flow in the direction. So that the wire is pulled out ward direction from all sides. According to Fleming's left hand rule, force on wire will act outward i direction from all sides.
Question 4.
Predict the polarity of the capacitor in a closed circular loop when two bar magnets are moved as shown in the figure.
Answer:

When magnet 1 is moved with its South pole towards to the coil, emf is induced in the coil as the magnetic flux through the coil changes. When seeing from the left hand side the direction of induced current appears to be clockwise. When seeing from the right hand side the direction of induced current appears to be anti-clockwise. In capacitor, plate A has positive polarity and plate B has negative polarity.
Question 5 .
In series LC circuit, the voltages across L and C are $180^{\circ}$ out of phase. Is it correct? Explain.

Answer:
In series LC circuit, the voltage across the capacitance lag the current by $90^{\circ}$ while the voltage across the inductance lead the current by $90^{\circ}$. This makes the inductance and capacitance voltages $180^{\circ}$ out of phase.
Question 6.
When does power factor of a series RLC circuit become maximum?
Answer:
For a series LCR circuit, power factor is
$\operatorname{Cos} \phi=\frac{\mathrm{R}}{\sqrt{\mathrm{R}^2+\left(\omega \mathrm{L}-\frac{1}{\omega \mathrm{C}}\right)^2}}$
$\left[\omega \mathrm{L}=\frac{1}{\omega \mathrm{C}}\right]$
For purely resistive, $\Phi=0^{\circ}, \cos 0^{\circ}=1$
Thus the power factor assumes the maximum value for a purely resistive circuit.
Question 7.
Draw graphs showing the distribution of charge in a capacitor and current through an inductor during LC oscillations with respect to time. Assume that the charge in the capacitor is maximum initially.
Answer:
For a capacitor, the graph between charge and time.

The charge decays exponentially decreases with time.