The magnetic field in a plane electromagnetic wave travelling in glass (n = 1.5) is given by By =(210^ -7 T)sin( alphax + 1 * 5 * 10 ^ 11 )

The magnetic field in a plane electromagnetic wave travelling in glass (n = 1.5) is given by
B y =(210^ -7 T)sin( alphax + 1 * 5 * 10 ^ 11 )
where x is in metres and t is in seconds. The value of a is:
(A) 0 * 5 * 10 ^ 3 * m ^ – 1
(B) 6 * 10 ^ 2 * m ^ – 1
(C) 7 * 5 * 10 ^ 2 * m ^ – 1
(D) 1 * 5 * 10 ^ 3 * m ^ – 1

Correct Answer: (C) 7.5×102 m−1