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Bite-Size Physics

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Here’s a lesson that you’ll get a charge out of! Now that you’ve spent the last two lessons learning about the strange world of the atom, this lesson we’re going to play with them.

Electrical Charges

Different parts of the atom have different electrical charges. The proton has a positive charge, the neutron has no charge (neutron, neutral get it?) and the electron has a negative charge. These charges repel and attract one another kind of like magnets repel or attract. Like charges repel (push away) one another and unlike charges attract one another. So if two items that are both negatively charged get close to one another, the two items will try to get away from one another. If two items are both positively charged, they will try to get away from one another. If one item is positive and the other negative, they will try to come together.

How do things get charged?

Generally things are neutrally charged. They aren’t very positive or negative. However, occasionally (or on purpose as we’ll see later) things can gain a charge. Things get charged when electrons move. Electrons are negatively charged particles. So if an object has more electrons than it usually does, that object would have a negative charge. If an object has less electrons than protons (positive charges), it would have a positive charge. How do electrons move? It turns out that electrons can be kind of loosey goosey. Depending on the type of atom they are a part of, they are quite willing to jump ship and go somewhere else. The way to get them to jump ship is to rub things together. Let’s play with this a bit and see if we can make it more clear.

 

 

Experiment 1

Charge It!

 

You need:

Balloon

Spoon

Pencil

Plastic straw

Something wool (scarf or sweater)

Towels or shirts made of different materials (cotton, polyester, etc)

Your hair

Strip of paper (1 inch by 8 inches or so)

Tape

1. Take the strip of paper and tape it to the table so that it hangs down and can swing freely.

2. Rub the balloon on your hair.

3. Slowly move the balloon close to the strip of paper and watch what the paper does. It should be attracted to the balloon and come closer to it.

4. Try rubbing other things on more stuff. The pencil on the shirt, the straw on the wool sweater etc. Have fun and feel free to try whatever you want to try.

5. Hold each thing close to the paper and see what happens.

6. If you’d like, you can write down what attracted the paper. Be sure to write what the object was and what it was rubbed against.

If the paper was attracted to the object, you’ve charged the object. You either rubbed more electrons on to the object, making it negative. Or you rubbed electrons off of the object, making it positive. Electrons will jump to whatever is more attractive to them. When you rub the balloon on your head, the electrons come out of your hair and onto the balloon. When you rub one thing against another thing, electrons may move to the more attractive thing, leaving one thing positive and the other thing negative (unless it’s grounded which we will talk about more next lesson). Did all the things you tried attract the paper? Probably not. Some objects hold their electrons fairly tightly so those objects can be difficult or impossible to charge. The spoon and the pencil probably did not get charged. By the way, the paper is not charged. “But Jim, you said opposite charges attract. How could the paper be attracted to things if it’s not charged?” Another excellent question. Things can be temporarily charged by a charged body being held near them. Next lesson we will talk more about that as well. For now we will just say that if the paper moved, the object we rubbed is charged.

 

Experiment 2item4

Charge Detector

 

You need:

Scotch tape

Balloon

Your hair

 

1. Rip off a piece of tape about three inches long.

2. Now stick it to the table. Rub the tape a bit and then rip it off the table.

3. Stick just the end of the tape to the edge of the table so that it dangles down from the table. What you’ve made is a charge detector.

4. Slowly bring your hand towards the dangling tape. You should notice that the tape is attracted to your hand. If it is, you’ve charged the tape.

5. Let’s find out what charge the tape is. Rub a balloon against your hair (or a shirt if you have a fancy hair do). Balloons are very attractive to electrons and so they are almost always negatively charged.

6. Now bring the balloon slowly to the tape and see whether the tape is attracted to, or repelled from the balloon. Usually, the tape is repelled.

If the tape is repelled from the balloon, what is the charge on the tape? Remember, opposite charges attract, same charges repel. So if the balloon is negative, and it repels the tape, then the tape is negative. Now that we know that, let’s try this.

Experiment 3

What’s the Charge Officer?

 

You need:

Balloon

Spoon

Pencil

Plastic straw

Something wool (scarf or sweater)

Towels or shirts made of different materials (cotton, polyester, etc)

Your hair

Charge Detector (made in experiment 2)

 

1. Recharge your charge detector by removing it from the table and sticking the entire piece of tape to the table. Rub it a little and then rip it off again. Now tape just the end to the edge of the table and let it dangle. You are going to want to recharge your tape after each trial.

2. Now rub different things together and hold them near the tape. Do they repel or attract the tape?

3. If you’d like, you can write down what attracted and repelled the tape. Be sure to write what the object was and what it was rubbed against.

So what did you find? You probably found a few things that attracted the tape and a few things that repelled the tape. So, can you tell what the charges of the things are? Yes you can...and well, no you can’t. You can certainly tell which of the things you used have a negative charge. If the charged object repelled the tape, then you’ve got a negative charge. However, if the charged object attracted the tape, then you can’t be so sure. You may have a positively charged object (opposites attract right), but you may have an object that has no charge. Notice how the tape is attracted to your hand. Your hand is not positive. It’s neutral. Remember above, when I said that sometimes things can have a temporary charge when close to something that’s electrically charged. Well, that is what’s happening with your hand and could be happening with whatever else attracted the tape. Hmmm, so how can you tell if something is positively charged? One way is to ground the tape. Keep touching it until it is no longer attracted to your hand. When that happens the tape has no charge. Now take the object that was attracted to the tape before, charge it up and see if the tape is attracted to it now. If it is, the object probably does have a positive charge. If it is attracting the tape now, it must have a charge (it’s creating a temporary charge on the tape) and since it attracted the tape when the tape had a negative charge, the charge on the object must be positive since opposites attract.

 

Experiment 4item5

A Hair Raising Experience

 

You need:

A balloon

Hair (Sorry Grandpa Joe!)

1. Rub the balloon on your hair.

2. Hold the balloon a few inches above your head.

Your hair is attracted to the balloon so it stands up. Again, this is a temporary charge (more next lesson). If your hair is attracted to the balloon, what is the temporary charge on your hair? Positive, yes. Notice how many of your hairs are staying as far away from one another as possible. Why do you think that is? Well if each hair is positive and like charges repel, your hair is repelling itself! That’s why it not only stands up, but stands out as well!

Next month we will talk more about static electricity, temporary charges, and electric shocks. If you got a charge out of this lesson, you’ll be shocked by the next one! (Sorry, couldn’t help myself!)

 

 

Different parts of an atom have different charges.

Neutrons are neutral (they have no charge).

Protons are positively charged.

Electrons are negatively charged.

If an item has more electrons than protons, it is said to be negatively electrically charged.

If an item has fewer electrons than protons, it is said to be positively electrically charged.

Electrons can move from some objects to other objects.

Electrons can move if objects are rubbed against one another.

Opposite charges attract one another.

Same charges repel one another.

Something that is charged can create a temporary charge in something else (more about this next month).

 

 

1. What is the charge on a proton?

2. What is the charge on a neutron?

3. What is the charge on an electron?

4. What moves to create static electricity?

5. If something has a negative charge, does it have too many electrons or too few?

6. If something moves away from a negatively charged object, is that something positively or negatively charged?

7. If something moves towards a positively charged object, is that object positive or negative?

8. Two neutrons walk into a fast food shop. After they order their food what does the cashier say?

9. Why don’t electrons get invited to parties?

 

Answers

1. Positive

2. Neutral

3. Negative

4. Electrons move from one object to another.

5. Too many. Electrons are negative.

6. Negatively charged. Same charges repel.

7. Negative...maybe. It may just have a temporary charge and as such be attracted.

8. For you...no charge. (Get it, they’re nuetrons!)

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