Question 12 of 20

The electric field associated with an electro magnetic wave in vacuum is given by E=i 40coskz-6×108t,where E,z and t are in volt/m, metre and second respectively.The value of wave vector k is 

(a) 2 m-1                               (b) 0.5 m-1

(c) 6 m-1                               (d) 3 m-1