Thread: Questions about Capacitors, Switches, Radio, experts wanted.

I've always wondered, and asked a lot of people (their answers never make sense to me) about the difference between a switch and a capacitor, or more specifically, how a capacitor works. Everyone says it's "two plates (or wires, doesn't matter unless you want a specific amount of farads, but this is capacitors in general) separated by an insulator." Some add a "like air" at the end. But between the connections of a switch is air. Both are essentially similar in design, because both are conductors attatched to a power source separated by an insulator. So, in that case, is a switch a very inefficient capacitor? Is there a spike of current when a switch is turned on? Is a battery by itself a crappy capacitor?
Now others say that a semiconductor is the middle layer between a capacitor, not an insulator, but I'm calling bs, because capacitors predate semiconductors and I have seen huge capacitors with air between them... Can someone clear me up on this? Especially because I was also taught that electricity stops flowing if the wires aren't connected... But that was 5th grade, and they didn't need to confuse us with capacitance. So recap, are switches crappy capacitors? And do stronger currents need bigger switches? Is there a current spike upon turning on a circuit's switch? What's the difference between a capacitor and a spark gap? How do capacitors work in a complex printed circuit or whatever if it follows the path of least resistance and goes around the capacitor, or are there diodes to prevent that happening?
Next, radio. Is it really just electricity vibrating around a piece of metal, like vibrations along a tuning fork? How can it do that if it goes from one wire to the other without "bouncing"? And it's AC... but with a frequency in the megahertz range??? How the heck do they get AC currents so high in frequency? My dad told me it was just a capacitor(>.<) with such a low capacitance, it almost immediately discharges, producing (not quite AC per se, but with all the flux still involved) a very jittery current rapidly turning on and off. Is that an industrial method for producing megahertz AC? Or do they use something to do with crystals? I've been hearing about those too. Where can I figure out how those work? Or, what do I look up on wikipedia?
I have heard that radio waves hitting metal make AC electricity with the frequency of the radio wave. But it's obviously too weak to use, or we would be using it. Again, where do I learn more? And I'm assuming people use a transistor to amplify currents in a regular radio, correct? Is a small amount of DC current being produced by radio waves hitting a diode, causing the electrons to travel one way across the diode, DC?
Lastly how can you change the radio signals your antennae picks up (or relays to the speakers)? Something to do with variable capacitance? Is that directly relevant to the AC frequency of the amplified current being charged and discharged in equilibrium with the capacitor? So much to learn. I realize I've asked a lot...

Originally Posted by Pomegranate Cameron

I've always wondered, and asked a lot of people (their answers never make sense to me) about the difference between a switch and a capacitor, or more specifically, how a capacitor works. Everyone says it's "two plates (or wires, doesn't matter unless you want a specific amount of farads, but this is capacitors in general) separated by an insulator." Some add a "like air" at the end. But between the connections of a switch is air. Both are essentially similar in design, because both are conductors attatched to a power source separated by an insulator. So, in that case, is a switch a very inefficient capacitor? Is there a spike of current when a switch is turned on? Is a battery by itself a crappy capacitor?

A switch does have some capacitance. This is usually not important but can be at high frequency. The obvious difference is that the switch has moving parts, so it changes from a very high impedance device (but not infinite) to a very low impedance device when you close it. A capacitor doesn't do that. There can be a spike when a switch is turned on, especially if there is something in the circuit like a charged capacitor that discharges in the initial spike. Usually in most circuits, the current is closer to a step than a spike when you close a switch. A battery has some capacitance as well, but I wouldn't call it a crappy capacitor. It uses chemical energy, unlike capacitors, which only store energy.

Now others say that a semiconductor is the middle layer between a capacitor, not an insulator, but I'm calling bs, because capacitors predate semiconductors and I have seen huge capacitors with air between them... Can someone clear me up on this? Especially because I was also taught that electricity stops flowing if the wires aren't connected... But that was 5th grade, and they didn't need to confuse us with capacitance.

There is often a material called a dielectric (not semiconductor) between the plates of a capacitor. Air can be the dielectric, but some other materials have desirable properties.

So recap, are switches crappy capacitors? And do stronger currents need bigger switches?

Stronger currents need bigger switches. The metal in a switch has some resistance and will heat up in proportion to the current flowing through it. With enough current, the plastic parts of the switch will melt or burn, or if there is enough current the metal will melt. That's why you need a bigger switch.

Is there a current spike upon turning on a circuit's switch? What's the difference between a capacitor and a spark gap? How do capacitors work in a complex printed circuit or whatever if it follows the path of least resistance and goes around the capacitor, or are there diodes to prevent that happening?
Next, radio. Is it really just electricity vibrating around a piece of metal, like vibrations along a tuning fork? How can it do that if it goes from one wire to the other without "bouncing"? And it's AC... but with a frequency in the megahertz range??? How the heck do they get AC currents so high in frequency? My dad told me it was just a capacitor(>.<) with such a low capacitance, it almost immediately discharges, producing (not quite AC per se, but with all the flux still involved) a very jittery current rapidly turning on and off. Is that an industrial method for producing megahertz AC? Or do they use something to do with crystals? I've been hearing about those too. Where can I figure out how those work? Or, what do I look up on wikipedia?
I have heard that radio waves hitting metal make AC electricity with the frequency of the radio wave. But it's obviously too weak to use, or we would be using it. Again, where do I learn more? And I'm assuming people use a transistor to amplify currents in a regular radio, correct? Is a small amount of DC current being produced by radio waves hitting a diode, causing the electrons to travel one way across the diode, DC?
Lastly how can you change the radio signals your antennae picks up (or relays to the speakers)? Something to do with variable capacitance? Is that directly relevant to the AC frequency of the amplified current being charged and discharged in equilibrium with the capacitor? So much to learn. I realize I've asked a lot...

You need to start off by learning some basic electrical theory. A class in school would be best but I think you could probably learn quite a bit by reading an online tutorial, like this one for example.
http://www.electronicstheory.com/