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. $1.2\times10^{-8} \hat{j}~\text{T}$

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. $2.1\times10^{-5}~\text{N}$

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: