A parallel plate capacitor with circular plates of radius 1 m has a capacitance of 1 nF. At t = 0, it is connected for charging in series with a resistor R = 1 M$\Omega$ across a 2V battery (as shown in the figure). Find the magnetic field at a point P, halfway between the centre and the periphery of the plates, after t = 10^–3 s. (The charge on the capacitor at time t is q (t) = CV[1 – exp (–t/$\tau$)], where the time constant $\tau$ is equal to CR.) 

$1. 0.74\times {10}^{-13} T$
$2. 0.67\times {10}^{-13} T$
$3. 0.74\times {10}^{-12} T$
$4. 0.67\times {10}^{-12} T$

A plane electromagnetic wave of frequency \(25 ~\text{MHz}\) travels in free space along the \(x\text-\)direction. At a particular point in space and time, $$\(\vec{E_{0}}=6.3 \hat{j}~\text{V/m}.\) What is \(\vec{B_{0}}\) at this point?
1. \(2.1\times 10^{-8} \hat{k}~\text{T}\)
2. \(1.2\times10^{-8} \hat{k}~\text{T}\)
3. \(2.1\times10^{-8} \hat{j}~\text{T}\)
4. \(1.2\times10^{-8} \hat{j}~\text{T}\)$\mathrm{}$

Light with an energy flux of \(18~\text{W/cm}^{2}\) falls on a non-reflecting surface at normal incidence. If the surface has an area of \(20~\text{cm}^{2}\), what is the average force exerted on the surface during a \(30\) minute time span?
1. \(2.1\times10^{-6}~\text{N}\)
2. \(1.8\times10^{-6}~\text{N}\)
3. \(1.2\times10^{-6}~\text{N}\)
4. \(2.1\times10^{-5}~\text{N}\)$\mathrm{}$

Assume a bulb of efficiency \(2.5\%\) as a point source. The peak values of the electric field and magnetic field produced by the radiation coming from a \(100~\text{W}\) bulb at a distance of \(3~\text{m}\) are respectively: