# Stuck with some textbook questions.

Discussion in 'Homework Help' started by Castelat, Jul 21, 2013.

1. ### Castelat Thread Starter New Member

Jul 21, 2013
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Hello, I'm stuck in doubt with these questions, my answers are in brackets but I'm not sure, please help me, I will really appreciate it:

- When several circuits are connected together to accomplish a task, this group of circuits is often referred to as a [system].

- On a circuit board, a printed wire is called a [conductor].

- When a component maintains a constant voltage across its terminals even if the amount of current passing through it changes is called a [Capacitor].

- A sandwich made of two conducting materials separated by a non-conducting material is commonly called a [PN Junction or Electrolyte?].

2. ### Castelat Thread Starter New Member

Jul 21, 2013
12
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maybe the last one is a semiconductor?

3. ### WBahn Moderator

Mar 31, 2012
18,085
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The first one is a reasonable answer.

The second one is true, but the term "trace" or "track" is more common.

Does the voltage on a capacitor change as the amount of charge on it changes? Doesn't a current result in a changing charge?

How do you construct the following: resistor, inductor, capacitor? Which of those meets the description provided.

4. ### Castelat Thread Starter New Member

Jul 21, 2013
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Well, I'm just a beginner, and of what I know the capacitor opposes any change in voltage, and the coil opposes any change in current. So the capacitor will always have the same voltage, and the coil will always have the same current. Therefore the capacitor will meet the description, capacitor is my answer.

How about a wafer made of two conducting materials separated by a non-conducting material, how is it called.

5. ### LDC3 Active Member

Apr 27, 2013
920
160
There is some misunderstanding of what you were told.

Yes a coil will resist a change in current, but the current will still change. When the coil is disconnected from a battery, there cannot be any current flowing through it. After connecting the coil to the battery, you can detect a magnetic field, which is caused by the current flowing in the coil. If a coil was to totally oppose a change in current, the magnetic field would never develop since no current would flow through the coil.

The same is true for a capacitor. It resist a change in voltage, but can not totally resist the change.

6. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
Don't sell yourself short, you must have already covered a large amount of ground to be attempting those questions and providing your answers.

However you seem to have capacitors and semiconductors mixed up, so what do you know about each?

7. ### MrChips Moderator

Oct 2, 2009
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3) voltage source, voltage regulator, voltage reference

4) capacitor

8. ### LDC3 Active Member

Apr 27, 2013
920
160
MrChips, you should know better. This is a homework question and providing answers does not help the person understand the problem, nor will assist in answering similar questions in the future.

9. ### Castelat Thread Starter New Member

Jul 21, 2013
12
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Thanks, I'll take note.

10. ### MrChips Moderator

Oct 2, 2009
12,624
3,451
I'm in a good mood today.

11. ### Castelat Thread Starter New Member

Jul 21, 2013
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Yeah maybe, I know electrolytic capacitors are made of some sandwich thing inside them, and semiconductors have this N-type and P-type thing, and sometimes even have a "barrier" in the middle like Diodes, but as I said I'm a beginner, I just started an electronics technician class 2 weeks ago, this is all I know, and these are some questions I have for homework.

I have to go now, I'll come later. thanks for your help.

12. ### Castelat Thread Starter New Member

Jul 21, 2013
12
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Thank you Chips, I'll try to figure it out how is that, hehe. have a good day.

13. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
The "hehe" says it all.

You won't try at all. You've had the answers handed to you and so you can put them on your homework and get credit and that's good enough for you.

Thanks a lot, MrChips.

14. ### MrChips Moderator

Oct 2, 2009
12,624
3,451
Sorry. Maybe that's the last time I'll do someone's homework for them.

15. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
"do their homework for them"... I hope so.

Help them do their own homework... keep right on doing that. You usually do a good job.

We all slip up -- I know I have.

16. ### Castelat Thread Starter New Member

Jul 21, 2013
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The “hehe” meant “I sympathize with you”.

eh?

How do you know I won’t try at all?, I've got 30 questions, and I've been thinking over and over since last Thursday when they handed me these questions. And believe it or not my first answer for the third one was “DC voltage source”, but then I doubt, I hardly ask for help, and I know a voltage source keeps a constant in voltage across its terminals, like a battery for example, but since is a source of voltage (maybe I’m wrong with this) and therefore current, I wasn't really sure if the current was proportional to the voltage of it, and I really don’t know how current works or runs inside a voltage source.

I’m still not sure about the last one though, since it can be a capacitor or a semiconductor as I pointed out, (I said electrolyte thinking about an electrolytic capacitor.)

Capacitor:

metal foil (conductor)

dielectric (non-conductor)

metal foil (conductor)

Semiconductor:

P-type (conductor)

PN-Junction (non-conductor)

N-type (conductor)

my native language is no English, sorry.

17. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515

Capacitors (electrolytic or otherwise) have two plates of conducting material that are separated by a layer of non conducting material in a sandwich.

A technician needs to know that this gives a capacitor two terminals to connect to, this leads to their circuit symbol, which you should look up and become familiar with.

In electronics we do not use plain semiconductors much - they are used for acoustic resonators and many other transducers.

You should look up what a transducer is.

However adding certain other material (called dopants) to the semiconductor changes its electrical properties, by increasing its electrical conductivity, which is another way of saying decrease its electrical resistance.
There are two types - those which decrease the resistance to negative charge carriers or n type and those which decrease the resistance to positive charge carriers or p type.

If we take a lump of n type and connect it to a lump of p type by a short wire or even touch them together nothing much of interest happens.

But if we introduce both types of dopant into one bar of semiconductor so that there is an internal interface between the p region and the n region we create a p-n junction.

Note there is no physical barrier within the single bar. However this junction has the special property that current flows more easily one way through it than the other. The details are uneccessary at this stage but this is the origin of your idea that there is a 'barrier'. This barrier is not a physical one but a voltage that has to be overcome.

Hope this helps and your studies go well.

Remember there is plenty of help available here for those with the right approach.

18. ### Castelat Thread Starter New Member

Jul 21, 2013
12
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oh ok, that seems pretty clear from you, It helped. I had it wrong about the inside of some semiconductors, which was the base of my confusion.

Thank you guys, all of you.

19. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
A capacitor is, almost by definition, two conductors separated by a non-conductor.

A PN junction is not an insulator, nor is it a layer that is placed between the P and the N regions. When an N-type material and a P-type material are placed in contact (or, more accurately, created in contact with each other), the carriers from one diffuse into the other creating an intrinsic electric field that builds until the amount of diffusion creates enough of a field to prevent further diffusion. If an external electric field is applied it can be applied so as to enhance the intrinsic field, and thus even futher prevent current from flowing, or so as to decrease the intrinsic field, so as to permit current to flow. This is why diodes conduct only in one direction.

The junction does exhibit capacitance, but this is very seldom why the device is created. Such capacitance is termed "parasitic" capacitance and is usually unwanted and degrades circuit performance.

20. ### vk6zgo Active Member

Jul 21, 2012
677
85
Varicaps,any one?