Question

2. An electromagnetic wave traveling in the -x direction in vacuum has a frequency 2x1014Hz. The electric field in the wave has maximum value of 2 V/m. If we define the time and position such that the electric field has maximum value at position x=0 at time=0, a possible equation describing the electric field is: a. É = (2 V/m) sin [(4.2 x 106 /m)x - (1.3 x1015 Hz)t] Î b. E = (2 V/m) cos[(4.2 x 106 /m)x + (1.3 x1015 Hz)t] & C. = (1 V/m) sin [(1.3 x 1015 /m)x - (4.2 x10 Hz)t] Â d. } = (4 V/m) cos [(4.2 x 106 /m)x+ (1.3 x1015 Hz)t] î

An electromagnetic wave traveling in the -x direction in vacuum has a frequency 2x1014Hz. The electric field in the wave has maximum value of 2 V/m. If we define the time and position such that the electric field has maximum value at position x=0 at time=0, a possible equation describing the electric field is:

"⃗
a. ?=(2V/m)sin[(4.2x106 /m)x-(1.3x1015Hz)t]?̂

"⃗ ' b. ?=(2V/m)cos[(4.2x106 /m)x+(1.3x1015Hz)t]?

"⃗ ' c. ?=(1V/m)sin[(1.3x1015 /m)x-(4.2x106Hz)t]?

"⃗
d. ?=(4V/m)cos[(4.2x106 /m)x+(1.3x1015Hz)t]?̂

Answer 1

2.

Option B is the right answer

Ē = 2(V/m) cos(1 – t)

E = 2(V/m)cos(4.2 * 10x +1.3 * 1015)

Substituting x=0, t=0 in the options should give the maximum value of electric field which is given as 2 V/m. Only option B satisfies this condition.