An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure $p$ on it. Which of the following are true?
Why is the orientation of the portable radio with respect to broadcasting station important?
The orientation of the portable radio with respect to broadcasting station is important because the electromagnetic waves are plane polarised, so the receiving antenna should be parallel to the vibration of the electric or magnetic field of the wave.
Why does microwave oven heats up a food item containing water molecules most efficiently?
Microwave oven heats up the food items containing water molecules most efficiently because the frequency of microwaves matches the resonant frequency of water molecules.
The charge on a parallel plate capacitor varies as $q=q_0 \cos 2 \pi v t$. The plates are very large and close together (area $=A$, separation $=d$ ). Neglecting the edge effects, find the displacement current through the capacitor.
The displacement current through the capacitor is,
$$I_d=I_c=\frac{d q}{d t}\quad\text{... (i)}$$
Here, $$\quad q=q_0 \cos 2 \pi v t \text { (given) }$$
Putting this value in Eq (i), we get
$$\begin{aligned} & I_d=I_c=-q_0 \sin 2 \pi v t \times 2 \pi v \\ & I_d=I_c=-2 \pi v q_0 \sin 2 \pi v t \end{aligned}$$
'A variable frequency AC source is connected to a capacitor. How will the displacement current change with decrease in frequency?
$$\begin{aligned} & \text { Capacitive reaction } X_c=\frac{1}{2 \pi f C} \\ & \therefore \quad X_c \propto \frac{1}{f} \end{aligned}$$
As frequency decreases, $X_{\mathrm{c}}$ increases and the conduction current is inversely proportional to $X_c\left(\because I \propto \frac{1}{X_c}\right)$.
So, displacement current decreases as the conduction current is equal to the displacement current.