JEE Main 201511 AprilOnline
- Exam
- JEE Main
- Year
- 2015
- Date
- 11 April
- Mode
- Online
- Subject
- Physics
- Chapter
- Electromagnetic Waves
JEE Main 2015 · 11 April · Online · Physics · Electromagnetic Waves
For plane electromagnetic waves propagating in the + z -direction,...
For plane electromagnetic waves propagating in the -direction, which one of the following combinations gives the correct possible direction for and field respectively?
Options
- A\left(\overset{^}{i} + 2\overset{^}{j}\right) and \left(2\overset{^}{i} - j\right)
- B\left(- 2\overset{^}{i} - 3\overset{^}{j}\right) and \left(3\overset{^}{i} - 2\overset{^}{j}\right)
- C\left(2\overset{^}{i} + 3\overset{^}{j}\right) and \left(\overset{^}{i} + 2\overset{^}{j}\right)
- D\left(3\overset{^}{i} + 4\overset{^}{j}\right) and \left(4\overset{^}{i} - 3\overset{^}{j}\right)
Correct answer
B. \left(- 2\overset{^}{i} - 3\overset{^}{j}\right) and \left(3\overset{^}{i} - 2\overset{^}{j}\right)
Step-by-step solution
The direction of propagation of the electromagnetic waves is along .
Also
When is along - 2\overset{^}{i} - 3\overset{^}{j}
And is along 3\overset{^}{i} - 2\overset{^}{j}
Then \overset{\to}{E} \times \overset{\to}{B} = \left(- 2\overset{^}{i} - 3\overset{^}{j}\right) \times \left(3\overset{^}{i} - 2\overset{^}{j}\right)
= 4\overset{^}{k} + 9\overset{^}{k}
= 13\overset{^}{k} is along +ve direction also
Also
When is along - 2\overset{^}{i} - 3\overset{^}{j}
And is along 3\overset{^}{i} - 2\overset{^}{j}
Then \overset{\to}{E} \times \overset{\to}{B} = \left(- 2\overset{^}{i} - 3\overset{^}{j}\right) \times \left(3\overset{^}{i} - 2\overset{^}{j}\right)
= 4\overset{^}{k} + 9\overset{^}{k}
= 13\overset{^}{k} is along +ve direction also