Quiz on Chapter 25

Question 1

An electric charge on the r axis oscillates sinusoidally about the origin. A distant observer is located at a point on the *y axis.

(a) In what direction will the electric field oscillate at the observer’s location?
(b) In what direction will the magnetic field oscillate at the observer’s location?
(c) In what direction will the electromagnetic wave propagate at the observer’s location?

Answer 1

Y= Electromagnetic wave

X= Electric field

Z= Magnetic field (oscillates in the plane perpendicular to the electric field and is also perpendicular to the direction of propagation)

Question 2

Most of the galaxies in the universe are observed to be moving away from Earth. Suppose a particular galaxy emits orange light with a frequency of 5.000 x 10E14 H2. If the galaxy is receding from Earth with a speed oI 3325 km/s, what is the frequency of the light when it reaches Earth?

Answer 2

Question 3

NEED TO REWRITE ANSWER! Consider a spiral galaxy that is moving directly away from Earth with a speed V : 3.600 x 105 m/s at its center as shown in Figure 15-26. The galaxy is also rotating about its center, so that points in its spiral arms are moving with a speed of : 6.400 x 105 m/s relative to the center. If light with a frequency of 8.230 x 10^14 H2 is emitted in both arms of the galaxy, what frequency is detected by astronomers observing the arm that is moving (a) toward and (b) away from Earth (Measurements of this type are used to map out the speed of various regions in distant, rotating galaxies.)

Answer 3

Question 4

Dental X-rays: X-rays produced in the dentist’s office typically have a wavelength of 0.30 nm. What is the frequency of these rays?

Question 5

Communicating with a Submarine Normal radiofrequency waves cannot penetrate more than a few meters below the surface of the ocean. One method of communicating with submerged submarines uses very low frequenry (VLF) radio waves. What is the wavelength (in air) of a 10.0-kHz VLF radio wave?

Answer 5

Question 6

Explain why the “invisible man” would be unable to see.

Answer 6

• Presumably, an “invisible man” would be invisible because light passes through his body unimpeded
• If some light were reflected or absorbed, we would see this effect and the person would no longer be invisible
• For a person to see, however, some light must be absorbed by the retina
• This absorption would cause the invisible man to be visible