Ch. 24 Flashcards
A transmitting antenna is located at the origin of an x, y, z axis system and broadcasts an electromagnetic wave whose electric field oscillated along the y-axis. The wave travels along the +x axis. Three possible wire loops are available for use with a LC-tuned circuit to detect this wave. Which one of the loops will detect the wave?
A loop that lies in the xy plane
Why does the peak value of the emf induced in a loop antenna depend on the frequency of the electromagnetic wave?
Because, according to Faradays law of electromagnetic induction, the emf depends on how rapidly the magnetic field of the wave is changing and this is determined by the frequency of the wave.
The frequency of electromagnetic wave A is twice that of electromagnetic wave B. For these two waves, what is the ratio lambdaA/lambdaB of the wavelengths in a vacuum?
LambdaA/lambdaB = 1/2
Because both waves have the same speed.
If both the electric and magnetic fields of an electromagnetic wave double in magnitude, how does the intensity of the wave change?
The intensity increases by a factor of four
Suppose that the electric field of an electromagnetic wave decreases in magnitude. What happens to the magnitude of the magnetic field?
Decreases
An astronomer measures the Doppler change in frequency for the light reaching the earth from a distant star. From this measurement, can the astronomer tell whether the star is moving away from the earth or the earth is moving away from the star?
No. The same Doppler change results when the stat moves away from the earth and when the earth moves away from the star. Only the relative motion between the star and the earth can be detected.
Malus’ law applies to a setup, which shows the analyzer rotated through an angle theta and the polarizer held fixed. Does Malus’ law apply when the analyzer is held fixed and the polarizer is rotated?
Yes
In example 6, we saw that when the angle between the polarizer and analyzer is 63.4 degrees, the average intensity of the transmitted light drops to one-tenth of the average intensity of the incident unpolarized light. What happens to the light intensity that is not transmitted?
The light intensity that is not transmitted is absorbed by the polarizer and the analyzer. The polarizer absorbs one-half of the incident intensity, and the analyzer absorbs four-tenths of the incident intensity.
The drawing shows two sheets of polarizing material. The transmission axis of one is vertical, and that of the other makes an angle of 45 degrees with the vertical. Unpolarized light shines on this arrangement first from the left and then from the right. From which direction does at least some light pass through both sheets?
Unpolarized: from either direction
Horizontally polarized: from the right
Vertically polarized: from either direction
You are sitting upright on the beach near a lake on a sunny day, wearing Polaroid sunglasses. When you lie down on your side, facing the lake, the sunglasses don’t work as well as they do while you are sitting upright. Why not?
Because the transmission axis of the Polaroid material is nearly horizontal, in the same direction as the polarized light reflected from the lake
The drawing shows an x, y, z coordinate system. A circular loop of wire lies in the z, x plane and, when used with an LC-circuit, detects an electromagnetic wave. Which statement is true?
The wave travels along the z axis, and its electric field oscillates along the x axis.
An electromagnetic wave is traveling in a vacuum. The magnitudes of the electric and magnetic fields of the wave are ___, and the electric and magnetic energies carried by the wave are ___.
Proportional (but not equal) to each other ; equal
An electromagnetic wave travels in a vacuum. The wavelength of the wave is tripled. How is this accomplished?
By reducing the frequency of the wave by a factor of three
The drawing shows two sheets of polarizing material. Polarizer 1 has its transmission axis aligned vertically, and polarizer 2 has its transmission axis aligned at an angle of 45 degrees with respect to the vertical. Light that is completely polarized along the vertical direction is incident either from the far left or from the far right. In either case, the average intensity of the incident light is the same. Which statement is true concerning the average intensity of the light that is transmitted by the pair of sheets?
When the light is incident from the left, the transmitted intensity is one-half the incident intensity
When the light is incident from the right, the transmitted intensity is one-fourth the incident intensity
