24.2 Production of electromagnetic waves  (Page 5/16)

A wave is travelling through a medium until it hits the end of the medium and there is nothing but vacuum beyond. What happens to a mechanical wave? Electromagnetic wave?

1. reflects backward, continues on
2. reflects backward, reflects backward
3. continues on, continues on
4. stops, continues on

You’re on the moon, skipping around, and your radio breaks. What would be the best way to communicate this problem to your friend, who is also skipping around on the moon: yelling or flashing a light? Why?

Given the waveform in [link] (d), if $T=3.0\times {10}^{-9}\text{s}$ and $E=5.0\times {10}^5\text{N / C}$ , which of the following is the correct equation for the wave at the antenna?

1. $\left(\text{5}\text{.0}\times {10}^5\text{N / C}\right)\text{sin}\left(\text{2}\pi \left(\text{3}\text{.0}\times {10}^{-9}\text{s}\right)t\right)$
2. $\left(\text{5}\text{.0}\times {10}^5\text{N / C}\right)\text{sin}\left(\frac{\text{2}\pi t}{\left(\text{3}\text{.0}\times {10}^{-9}\text{s}\right)}\right)$
3. $\left(\text{5}\text{.0}\times {10}^5\text{N / C}\right)\text{cos}\left(\text{2}\pi \left(\text{3}\text{.0}\times {10}^{-9}\text{s}\right)t\right)$
4. $\left(\text{5}\text{.0}\times {10}^5\text{N / C}\right)\text{cos}\left(\frac{\text{2}\pi t}{\left(\text{3}\text{.0}\times {10}^{-9}\text{s}\right)}\right)$

Given the waveform in [link] (d), if $f=2.0$ GHz and $E=6.0\times {10}^5\text{N/C}$ , what is the correct equation for the magnetic field wave at the antenna?

In Heinrich Hertz’s spark gap experiment ( [link] ), how will the induced sparks in Loop 2 compare to those created in Loop 1?

1. Stronger
2. Weaker
3. Need to know the tuner settings to tell
4. Weaker, but how much depends on the tuner settings.

The sun is far away from the Earth, and the intervening space is very close to empty. Yet the tilt of the Earth’s axis of rotation relative to the sun results in seasons. Explain why, given what you have learned in this section.

The direction of the electric field shown in each part of [link] is that produced by the charge distribution in the wire. Justify the direction shown in each part, using the Coulomb force law and the definition of $\mathbf{E}=\mathbf{F}/q$ , where $q$ is a positive test charge.

Is the direction of the magnetic field shown in [link] (a) consistent with the right-hand rule for current (RHR-2) in the direction shown in the figure?

Why is the direction of the current shown in each part of [link] opposite to the electric field produced by the wire’s charge separation?

In which situation shown in [link] will the electromagnetic wave be more successful in inducing a current in the wire? Explain.

In which situation shown in [link] will the electromagnetic wave be more successful in inducing a current in the loop? Explain.

Should the straight wire antenna of a radio be vertical or horizontal to best receive radio waves broadcast by a vertical transmitter antenna? How should a loop antenna be aligned to best receive the signals? (Note that the direction of the loop that produces the best reception can be used to determine the location of the source. It is used for that purpose in tracking tagged animals in nature studies, for example.)

Under what conditions might wires in a DC circuit emit electromagnetic waves?

Give an example of interference of electromagnetic waves.

[link] shows the interference pattern of two radio antennas broadcasting the same signal. Explain how this is analogous to the interference pattern for sound produced by two speakers. Could this be used to make a directional antenna system that broadcasts preferentially in certain directions? Explain.

Can an antenna be any length? Explain your answer.

What is the maximum electric field strength in an electromagnetic wave that has a maximum magnetic field strength of $5\text{.}\text{00}\times {\text{10}}^{-4}\text{T}$ (about 10 times the Earth’s)?

The maximum magnetic field strength of an electromagnetic field is $5\times {\text{10}}^{-6}\text{T}$ . Calculate the maximum electric field strength if the wave is traveling in a medium in which the speed of the wave is $\text{0.75}c$ .

Verify the units obtained for magnetic field strength $B$ in [link] (using the equation $B=\frac{E}{c}$ ) are in fact teslas (T).