JEE Main 2016 · 10 Apr · Shift 1 · Physics Q18

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PhysicsSingle correct+4 / -1Question 18 of 90

Consider an electromagnetic wave propagating in vacuum. Choose the correct statement :

For an electromagnetic wave propagating in +x direction the electric field is

\vec E=\dfrac1{\sqrt2}E_{yz}(x,t)\left(\hat y-\hat z\right)

and the magnetic field is

\vec B=\dfrac1{\sqrt2}B_{yz}(x,t)\left(\hat y+\hat z\right)

For an electromagnetic wave propagating in +x direction the electric field is

\vec E=\dfrac1{\sqrt2}E_{yz}(y,z,t)\left(\hat y+\hat z\right)

and the magnetic field is

\vec B=\dfrac1{\sqrt2}B_{yz}(y,z,t)\left(\hat y+\hat z\right)

For an electromagnetic wave propagating in +y direction the electric field is

\vec E=\dfrac1{\sqrt2}E_{yz}(x,t)\,\hat y

and the magnetic field is

\vec B=\dfrac1{\sqrt2}B_{yz}(x,t)\,\hat z

For an electromagnetic wave propagating in +y direction the electric field is

\vec E=\dfrac1{\sqrt2}E_{yz}(x,t)\,\hat z

and the magnetic field is

\vec B=\dfrac1{\sqrt2}B_z(x,t)\,\hat y

Answer and worked solution

Official answer: A

For a wave along +x the fields depend on (x, t), are perpendicular to each other and to x, and $\vec E\times\vec B$ points along +x. In (1), $(\hat y-\hat z)\times(\hat y+\hat z)=2\hat x$ , so all conditions hold. (2) has $\vec E\parallel\vec B$ ; (3) and (4) have fields depending on x for a wave said to travel along y, and (3) has E along the direction of travel.

Topics:Properties of EM waves

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JEE Main 2016 · 10 Apr · Shift 1, Physics question 18