Help with diodes and waves

[qdgjcl]

I’m reading a textbook on electronics, and I’m in the diode section. They show a circuit with one diode and a resistive load. The cathode is facing away from the AC voltage source. There is an arrow showing the current moving counter clockwise, and it says that only the positive half of the wave will be seen on the oscilloscope. I understand that the diode will only let current move through it from the cathode to the anode. Does that mean when I look at a circuit with a diode, and I want to predict which half of the wave will appear the negative half moves counter clockwise and positive moves clockwise?

Thanks for any help,
Brad

[bridgen]

In the circuit you describe the "negative half" doesn't move at all. The diode lets the current pass in only one direction.
If you reversed the diode it would let the current pass in only the other direction and you would see the negative half cylce across the resistor in your example.

[ad5mb]

The arrow points toward the negative side. If the "tail" of the arrow is positive and the target the arrow whacks is negative, current flows.<p>Current flows from negative to positive, so the direction of current flow is the opposite of the direction of the arrow.

[bodgy]

I sniff the Conventional versus Electron flow in the offing.<p>colin

[qdgjcl]

I understand that electrons flow from negative to positive, and current flows against the diode arrow. What I can't figure out is when the book asks, " will the output be negative or positive", when a diode is put in a circuit with an ac source. If the anode is hooked up to the ac source and the cathode is hooked to the resistor in series, I will see a positive output. Is this because I can assume that when the current is flowing counter clockwise the diode will let it pass and that counter clockwise flow will show up as a positive half of the sine wave on the?<p>Thanks,<p>Brad
osilliscope?

[bridgen]

Brad,
I've sent a private message which you should be able to access in your profile area.

[chessman]

Brad-<p>Okay, here goes:<p>A standard diode such as the one you are talking about will only pass current in one direction. That is, in your textbook circuit, the positive half of the wave will be passed through the diode, and the negative half will not.<p>To revert to the electron-flow version:<p>Electrons flow from negative to positive, as you know. So with a diode, the electrons flow into the cathode and out of the anode. That means to have conduction you will have to connect the cathode to the negative terminal and the anode to the positive terminal.<p>The above is called "forward biased". With your AC wave applied across the positive and negative terminals, there will be conduction on the positive half of the wave, but there will not be conduction on the negative half of the wave. So on the output, you would see the positive part of the wave, then a gap, then the next positive cycle, etc.<p>To simply answer your question, the output would be positive-only.<p>That is why diodes are used as "rectifiers", to make a mains AC signal positive-only.<p>Hopefully this helps,
~Kyle