SP212/3321&5521
Chapter 33 - Worksheet #1
Question 1: The figure below shows the electric field of an electromagnetic wave at some instant.
The wave it travelling to the right (the +x-direction). (a) What is the magnetic field vector at this
instant? Give both the magnitude and direction. (b) What is the Poynting vector at this instant?
Give both the magnitude and direction.
y
~v
x
+z is out of the page
~
E=(+925
N/C)ĵ
Question 2: An electromagnetic wave has an oscillating magnetic field given by
B =(0.0125 T)sin[(9.67 × 106 radians/m)x − (2.90 × 1015 radians/s)t]. (a) What is the intensity of
this light? (b) What is the wavelength of this light?
SP212/3321&5521
Chapter 33 - Worksheet #1
Question 3: A light bulb acts as a point source with a 120 W power output. Assume that all of this
power is output as light. (a) What is the amplitude of the oscillating electric field of the light given
off by this bulb at a distance of 4.5 m away? (b) What is the amplitude of the oscillating magnetic
field at this position. (c) What is the rms (root mean squared) value of the electric field at this
position?
Question 4: A square sheet of paper is 2.5 m long on each side. The paper is held perpendicular to a
bright light with an intensity of 1500 W/m2 . (a) If the paper is black and absorbs all of the incident
light, what is the magnitude of the force pushing on the paper? (b) Instead, assume that the paper
is shiny and perfectly reflects all of the incident light. What is the magnitude of the force pushing
on the paper?