Capacitors

Starting with Version 3.

In this writing, I use Past Tense-Present Tense (rather than Present Tense-Past Tense) for the story and explanation.

This page is assumed to come in the middle of the book, so it has several references to past events that are currently unexplained.

The final section "Capacitors in Nature" is off to the side (in a fancy box, perhaps).

Please help me with my transition. I want Rachel to explain the concepts to the reader without interrupting the story. She needs to break into this mode (pause-time or something) somehow.

-----------------------------------------------------

Capacitors

Kevin ran toward The Storm, excited to get a better view of the monstrous roller coaster. He called to Rachel, “Hey! Take my picture with this sign!” Kevin stood grinning next to a large board that said “The Storm” in letters shaped like lightning bolts.

Kevin ran toward The Storm, excited to get a better view of the monstrous roller coaster. He called to Rachel, "Hey! Take my picture with this sign!" Kevin stood grinning next to a large board that said "The Storm" in letters shaped like lightning bolts.

Rachel pulled out her disposable camera “Hold on, the board is casting a shadow on you. Let me charge the flash!”

Kevin waited patiently and a few seconds later he was attacked by a bright light. “Ouch. Why is that light so much stronger than the lamps we saw earlier? The camera is probably running on batteries! Shouldn't something running on batteries be much dimmer than something powered by the grid?”

Rachel apologized, “Sorry Kevin, I should have warned you that this flash was so bright.”

“I think this is a good time to meet our next circuit element,” Rachel exclaimed, “Introducing the Capacitor!”

~~~

A disposable camera battery has a lot of energy in it, but cannot release it quickly enough to make a bright flash. To make a flash, we need some sort of energy storage that can quickly dump all the energy through a light-bulb.

Capacitors are basically two conductors separated by an insulator. Capacitors can store energy by storing charge. Unlike resistors, capacitors do not let current flow directly through them. Remember that charges do not easily flow through insulators. When charges go in one side of the capacitor, they accumulate and store energy.

In a disposable camera, a battery charges the capacitor by using energy to force a current into one side of a capacitor. On some cameras, they tell you to hold down a button for “readying the flash”. When you press the button, the battery is connected to the capacitor and the capacitor charges. If you listen carefully, you can sometimes hear a whirring noise as this happens!

Now let’s think about what happens when we have a lot of negative charges collected on one side of the capacitor and a lot of positive charges on the other side. Recall that like-charges repel each other; these accumulated charges want to separate from each other if possible. What do you think will happen if we connect the two sides of a charged capacitor with a conductor? The charges will rush through the conductor away from other like-charges!

When you press the “take picture” button on a disposable camera, the two sides of the charged capacitor are connected by a light-bulb. A large current rushes through the light-bulb and the light-bulb releases the stored energy. If enough energy is stored, the result is a blinding flash of light!

~~~

“It’s okay, but I think we need to take another photo. I wasn’t ready. I closed my eyes!” Kevin laughed, rubbed his eyes, and posed in front of the sign again.

“Sure, I’ll take another photo. But if this small camera can scare you, I don’t know how you’re going to ride The Storm.”

##

Capacitors in Nature

You probably have seen capacitors in nature before. Thunderstorms are a good example of capacitors. Let’s say that the ground and the clouds are conductors and are separated by the insulating air. What does this make? A capacitor!

Charges collect on the clouds because of the rough weather. When enough charges collect, there is enough stored energy for the charges to break through the air. The charges that rush through the air cause the air to burn and energy is released in a bright flash! If you’re lucky enough to see this, you’ve just watched lightning strike.