QUIZ 22( TEST 3)

PROBLEMS TO TURN IN  : 3, 4, 11, 12, 16, 17, 40 

3. B = E/c, where B and E are the magnetic and electric field magnitudes respectively. See page 619.
4. See figure 22-7 and you will see Band E's special relationship, which is that the two vectors are perpendicular and  from their directions you can find the propagation direction. Here is how you can: With your right fingers, wrap the E-vector into the B vector and your thumb points in the propagation direction.  This is a another right hand rule we will be using .  Fig 22-7 says it all. The propagation direction is along the positive x-axis. Pay attention to the  wave form's left end  where the E-field vector is up along y.  Wrap your fingers into the B-vector  (which essentially points out of the page, along z)) and your thumb points right, along the propagation.  

In this problem do the same thing with your right hand. Here, your thumb direction is given, West. Let West be leftward along  the page.  Now, the B-vector oscillates up and down along the page. When the B-vector is upward, your right fingers will point outward in the direction of the E-vector and you will  wrap your fingers  upward into the B-vector.   Thus, the E-vector points out of the page when the B-vector is up. Repeat the same logic when the B-vector points down and you will find  the electric field  points into the page.   

Now for the magnitude of the vector E which we found oscillates  in and out of the page: Erms = c*Brms.  What is the frequency? 
11.
1 ly is the distance light travels in one year. Thus: 
1 ly = c*t, in meters (m), where c is the published speed of light and t = 1 year in seconds. 

Compute D = c*t , where t = 4.2 years in seconds. 
12. See problem 11. 
16.  Use D = v*t , where v = speed  sound,  D' = c*t', where = speed of light,  to compute t and t', t  = the time it takes sound to travel 50.0 m and t ' = time it takes light to travel 3000 km, respectively. Compare the times. 
17. Think of the  pulsed laser as a tube of tooth paste emitting toothpaste. The length of the tooth paste line = v*t, where v = speed of toothpaste front and t = time of paste flow.  Replace v with the speed of light and t with 32 picoseconds.
Divide this length by the wavelength of the light. See example 22-1.    
40. Use D = v*t , where v = speed  sound,  D' = c*t', where = speed of light,  to compute t and t', t = the time it takes sound to travel 25.0 m and t ' = time it takes light to travel from the Moon to the Earth, respectively.  Compare the times. Find t + t'.