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

1. \(0 . 74 \times 10^{- 13}~\text T\)
2. \(0 . 67 \times 10^{- 13}~\text T\)
3. \(0 . 74 \times 10^{- 12}~\text T\)
4. \(0 . 67 \times 10^{- 12}~\text T\)
$$

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: