The electric field on an electromagnetic wave in free space is given by
`E=10 cos (10^7t+kx) hatj V//m`,
Where t and x are in seconds and metres respectively. It can be inferred that
(1) the wavelength `lambda` is `188.4m`.
(2) the wave number k is `0.33rad//m`
(3) the wave amplitude is `10V//m`
(4) the wave is propagating along +x direction.
which one of the following pairs of statement is correct?

Options

A. (3) and (4)
B. (1) and (2)
C. (2) and (3)
D. (1) and (3)

Answer

D

Explanation

`vecE= 10 cos(10^(7)t+ kx) hatj V//m`
Amplitude= `10 V//m`
Speed(c)=`(omega)/(k)implies 3 xx 10^(8) = (10^(7))/(k) implies k=(1)/(30)`
Wavelenght `(lambda)= (2pi)/(k)= 2pi xx 30= 188.4 m`