C) the time variation of the magnetic flux.
D) current divided by time.
17. An electric generator transforms
A) electrical energy into mechanical energy.
B) mechanical energy into electrical energy.
C) direct current into alternating current.
D) alternating current into direct current.
18. If the electric field in an EM wave has a peak value of \( 2.0 \mathrm{~V} / \mathrm{m} \), what is the peak value of the magnetic field?
A) 6.7 nT
B) 2.0 T
C) \( 3.0 \times 10^{8} \mathrm{~T} \)
D) none of the given answers
19. An electromagnetic wave is traveling to the east. At one instant at a given point its \( \mathbf{E} \) vector points straight up. What is the direction of its B vector?
A) north
B) down
C) east
D) south
20. Is it possible to see a virtual image?
A) No, since the rays that seem to emanate from a virtual image do not in fact emanate from the image.
B) No, since virtual images do not really exist.
C) Yes, the rays that appear to emanate from a virtual image can be focused on the retina just like those from an illuminated object.
D) Yes, since almost everything we see is virtual because most things do not themselves give off light, but only reflect light coming from some other source.
E) Yes, but only indirectly in the sense that if the virtual image is formed on a sheet of photographic film, one could later look at the picture formed.
21. A light ray, traveling parallel to a concave mirror's axis, strikes the mirror's surface near its midpoint. After reflection, this ray
A) again travels parallel to the mirror's axis.
B) travels at right angles to the mirror's axis.
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