For a plane electromagnetic wave propagating in x-direction, which one of the following combination gives the correct possible directions for electric field (E) and magnetic field (B) respectively?
(1) $\hat j + \hat k, \hat j + \hat k $
(2) $-\hat j + \hat k, -\hat j – \hat k $
(3) $\hat j + \hat k, -\hat j – \hat k $
(4) $-\hat j + \hat k,-\hat j+\hat k $ Continue reading For a plane electromagnetic wave propagating in x-direction ….
A plane electromagnetic wave of frequency 500 MHz is travelling in vacuum along y-direction. At a particular point in space and time, $\vec B = 8.0 \times 10^{-8} \hat z T$. The value of electric field at this point is:
(speed of light = $3 \times 10^8 ms^{-1} $)
$\hat x , \hat y , \hat z $ are unit vectors along x, y and z directions.
(A) $24 \hat x V/m $
(B) $2.6 \hat x V/m $
(C) $-24 \hat x V/m $
(D) $-2.6 \hat y V/m $ Continue reading A plane electromagnetic wave of frequency 500 MHz ….
For an electromagnetic wave traveling in free space, the relation between average energy densities due to electric $(U_e)$ and magnetic $(U_m)$ fields is:
(A) $U_e > U_m $
(B) $U_e = U_m $
(C) $U_e \neq U_m $
(D) $U_e < U_m $ Continue reading For an electromagnetic wave traveling in free space ….
Electric field of a plane electromagnetic wave propagating through a non-magnetic medium is given by $E = 20\cos (2 \times {10^{10}}t – 200x)V/m$. The dielectric constant of the medium is equal to: (Take $\mu _r = 1 $)
(A) $\frac {1}{3}$
(B) 3
(C) 2
(D) 9
Solution
We have, $E = 20\cos \left[ {200\left( {\frac{{2 \times {{10}^{10}}}}{{200}}t – x} \right)} \right]V/m$
So, $v = \frac{{2 \times {{10}^{10}}}}{{200}} = 1 \times {10^8}m/s$
$\mu = \sqrt {{\mu _r}{\epsilon_r}} = \frac{c}{v} = \frac{{3 \times {{10}^8}}}{{1 \times {{10}^8}}} = 3$
$ \Rightarrow \sqrt {1 \times {\epsilon_r}} = 3$
$ \Rightarrow {\epsilon_r} = 9$ = Dielectric Constant
Answer: (D)
