Light with an energy flux of 18 W/cm² falls on a non-reflecting surface at normal incidence. If the surface has an area of 20 cm², what is the average force exerted on the surface during a 30 minute time span?

$$\begin{gathered} 1. 2.1\times {10}^{-6} \mathrm{N} \\ 2. 1.8\times {10}^{-6} \mathrm{N} \\ 3. 1.2\times {10}^{-6} \mathrm{N} \\ 4. 2.1\times {10}^{-5} \mathrm{N} \end{gathered}$$

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 100W bulb at a distance of 3m are respectively:

$$\begin{gathered} 1. 2.5 \mathrm{V}/\mathrm{m}, 2.2\times {10}^{-8} \mathrm{T} \\ 2. 3.6 \mathrm{V}/\mathrm{m}, 3.6 \mathrm{T} \\ 3. 4.07 \mathrm{V}/\mathrm{m}, 1.4\times {10}^{-8} \mathrm{T} \\ 4. 4.2 \mathrm{V}/\mathrm{m}, 3.4\times {10}^{-6} \mathrm{T} \end{gathered}$$

The magnetic field in a plane electromagnetic wave is given by$\mathrm{B}=\left(2\times {10}^{-7}\right)\mathrm{T} \sin \left(0.5\times {10}^3\mathrm{x}+1.5\times {10}^{11}\mathrm{t}\right)$. The wavelength and frequency of the wave are respectively:

$$\begin{gathered} 1. 2.16 \mathrm{cm}, 24.1 \mathrm{GHz} \\ 2. 0.29 \mathrm{cm}, 13.7 \mathrm{GHz} \\ 3. 3.23 \mathrm{cm}, 20.0 \mathrm{GHz} \\ 4. 1.26 \mathrm{cm}, 23.9 \mathrm{GHz} \end{gathered}$$

A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, $$\(\vec{E_{0}}=6.3~ \hat{j}~V/m\). What is \(\vec{B_{0}}\) at this point?

$$\begin{gathered} 1. 2.1\times {10}^{-8} \hat{\mathrm{k}} \mathrm{T} \\ 2. 1.2\times {10}^{-8} \hat{\mathrm{k}} \mathrm{T} \\ 3. 2.1\times {10}^{-8} \hat{\mathrm{J}} \mathrm{T} \\ 4. 1.2\times {10}^{-8} \hat{\mathrm{J}} \mathrm{T} \end{gathered}$$

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.) 

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