Explanation of the Graetz circuit

Question

My knowledge of circuits is pretty rudimentary and I've never really understood circuits, so I'm having trouble with the concept of Graetz circuits:

When you register the voltage on the resistor R on a screen of an oscilloscope, you get:

Why is this exactly? As I said, my knowledge of circuits is very limited. My idea:

The sign at the bottom of the circuit means it is an AC current. If the current goes from left to right it will be stopped by the diode above and let through by the diode below (to the left of the resistor) and vice versa if it goes from the right to the left. Is this correct?

Answer 1

You've correctly deduced how the circuit works. This particular configuration is better known as a bridge rectifier and is often packaged as a single component containing 4 diodes. There are two uses for this - rectifying alternating current as depicted in your question, and creating circuits that can handle direct current with reversed polarity (for instance, in the event a battery is inserted backwards).