# Electricity: 2 charged rods connected to a voltage source

## Homework Statement

In addition to the question given in the attached file below, I don’t understand how is the polarity changing periodically.

## Homework Equations

Concept-based question, I guess.

## The Attempt at a Solution

I have no idea how should I approach the question. So, if anyone has an idea, can he/she explain?

#### Attachments

• 0D62014F-47E8-40E9-B5BE-67B2BED786B1.jpeg
32.1 KB · Views: 203

RPinPA
Homework Helper
A generator producing Alternating Current (AC) would be an example of such a voltage source. First one side is at higher voltage, then the other, and they switch back and forth in a sinusoidal pattern.

The question is asking you what the effect is of the charge distribution changing back and forth between those two pictures periodically. What have you learned about changing charge distributions?

berkeman
Mentor
*
In addition to the question given in the attached file below, I don’t understand how is the polarity changing periodically.
As mentioned by @RPinPA a signal generator can make such a changing output voltage. The voltage between the two rods could vary with a sinusoidal function like:

V(t) = 1V * sin (2π * 1kHz * t), and you could alter the amplitude from 1V and the frequency from 1kHz if you want a different driven waveform.
I have no idea how should I approach the question. So, if anyone has an idea, can he/she explain?
For each of the 2 figures, draw the E field lines from + to - charges, just as you do for other geometries with charge separation. If you need help with that, try Google Images with appropriate search terms to get some ideas. With those two modified diagrams, you can partially answer the question.

To fully answer the question, search on "dipole antenna operation" or similar. Let us know what you find...

A generator producing Alternating Current (AC) would be an example of such a voltage source. First one side is at higher voltage, then the other, and they switch back and forth in a sinusoidal pattern.

The question is asking you what the effect is of the charge distribution changing back and forth between those two pictures periodically. What have you learned about changing charge distributions?
Ahh, apparently I didn’t learn something about this topic. So, I need to know changing charge distribution and AC.

*
As mentioned by @RPinPA a signal generator can make such a changing output voltage. The voltage between the two rods could vary with a sinusoidal function like:

V(t) = 1V * sin (2π * 1kHz * t), and you could alter the amplitude from 1V and the frequency from 1kHz if you want a different driven waveform.

For each of the 2 figures, draw the E field lines from + to - charges, just as you do for other geometries with charge separation. If you need help with that, try Google Images with appropriate search terms to get some ideas. With those two modified diagrams, you can partially answer the question.

To fully answer the question, search on "dipole antenna operation" or similar. Let us know what you find...

I don’t know a thing about the first part “
As mentioned by @RPinPA a signal generator can make such a changing output voltage. The voltage between the two rods could vary with a sinusoidal function like:

V(t) = 1V * sin (2π * 1kHz * t), and you could alter the amplitude from 1V and the frequency from 1kHz if you want a different driven waveform.“

But I do know how to draw electric fields. I am going to search more about the others ,and then come back to the question.

I have looked for dipole antenna and found that its like the ‘"rabbit ears" television antenna found on broadcast television sets’. There's a changing electric field throughout all the space because of the alternation and a changing electric field near the end of the rods. If the length is half a wavelength the will be radiation. So, I think the answer is D. Is my reasoning correct?

#### Attachments

• 005133AB-E1FF-4C64-BF02-4969D3AC8EFD.jpeg
56.6 KB · Views: 201
berkeman
Mentor
So, I think the answer is D. Is my reasoning correct?
Yes, good work!

YMMMA
Many thanks!
Yes, good work!

berkeman