About $20 \%$ of the power of a $100 \ W$ bulb is converted to visible radiation. Assuming that the radiation is emitted isotropically and neglecting reflection,the average intensity of visible radiation at a distance of $5 \ m$ is $\frac{\alpha}{25 \pi} \ W/m^2$. The value of $\alpha$ is

$A$ flood light is covered with a filter that transmits red light. The electric field of the emerging beam is represented by a sinusoidal plane wave
$E_x=36\,\sin\,(1.20 \times 10^7z -3.6 \times 10^{15}\,t)\,V/m$
The average intensity of the beam will be.....$W/m^2$

Which of the following statements is false regarding the properties of electromagnetic waves?

The ratio of the magnitudes of the electric field and $10^8$ times the magnetic field of a plane electromagnetic wave is

If the amplitude of the magnetic field in a travelling plane electromagnetic wave is $2.2 \times 10^{-4} \ T$,then the intensity of the wave is nearly

$A$ point light source emits electromagnetic ($E$.$M$.) waves in free space. $A$ detector, placed at a distance of $L \text{ m}$, measures the intensity as $I_o$. The detector is now shifted to another location on the same spherical surface, ensuring the angle between the original location and the new location is $45^{\circ}$. The measured intensity at the new location will be . . . . . . .