PURPOSE

Investigate the behavior of static electricity 

DISCUSSION, FILL THE BLANKS FOR FULL CREDITS (after watching movie)

( use words as: negatively, positively, positive, negative, electrons, ground,  rubbed, charges)

As seen in the movie, clothes removed from the dryer usually cling to each other and spark or crackle with static electricity when they are separated, When 2 dissimilar materials are ______________ together they can become _____________. Object can acquire static electric charges by either gaining or losing _____________. An object that gains ___________ has a net _________ charge and is said to be ______________ charged. An object that loses _____________has a net _____________ charge and is said to be ___________ charged. Only those objects separated from a ground or Earth, by an insulator will retain their charge for any length of time (capacitor or Leyden jar can hold charges). Objects that are attached to the _________ through a conductor will remain uncharged, since the charge travels into the ___________ and is quickly dissipated.

Remember the affinity chart ?

Hold electrons tightly 
brass
copper
ebonite (rubber)
wax
silk
lead
fur
wool, fur
glass
hold electrons lightly

According to this chart if you rub a hard rubber rod with wool or fur, the rod will become _____________ charged. Whereas, if you rub a glass rod with silk, the glass rod becomes ____________ charges. In this experiment, you will charge object and observe their interactions with other charges objects.

Materials

Hard rubber rod                                 wool pad

Glass rod                                            pith ball suspended by silk thread from holder

Plastic wrap or acrylic rod                 leaf electroscope

Silk pad                                              leyden jar                                       wire with alligator clip

Procedure

Try to perform the experiment in a cool dry day. (humidity take the charges away). You may have to be energy when rubbing the rods. 

Don’t hesitate to do an experiment several times. Take turn.

PARTII : Positively charging a pith ball

Step1: Touch the pith ball  with your fingers to discharge it.  (in case it got charges). 

Rub vigorously the hard rubber rod with the fur or wool pad to charge it vigorously  (the rod becomes negatively charged). 

Bring the rod close to , BUT NOT TOUCHING, the suspended pith ball, as shown in figure (above). Observe the behavior of the pitch ball and record your observations :

___________________________________________________________________________________________________________________

___________________________________________________________________________________________________________________

Explain what is happening. (it is called polarization, see PART 2, 3)

_______________________________________________________________________________________________________________________________________________

Step2:  Touch the pith ball with your finger to remove the any charge it may have (grounded).

Charge the robber rod again.  (rub vigorously) Bring it close to the pith ball and allow it to touch the ball. 

Then bring the charged rod near the charged ball (without touching it ) and observe the behavior of the ball. Record your observation:

___________________________________________________________________________________________________________________

Knowing that the rod was negatively charged, explain what happened :

____________________________________________________________________________________________________________________

PARTII : Positively charging a pith ball

Step1: Touch the pith ball with your finger to remove the any charge it may have (grounded).

Rub the glass rod with a piece of silk to charge it (it will be positively charged). Bring the rod close to, BUT NOT TOUCHING, a suspended pith ball. 

Observe the behavior of the pith ball and recode your observations:

_____________________________________________________________________________________________________________

WHat happened ?_____________________________________________________________________________ (polarization)

Touch the pith ball with your finger to remove any charge any charge it may have.

Step2: Charge the glass rod again. Bring it to the pith ball and allow it to touch the ball. Then bring the charged rod near the charged ball (don't touch)

and observe the behavior of the pith ball: 

___________________________________________________________________________________________________________

what happened ? _______________________________________________________________________________________________

PART III: charging the electroscope by conduction

Step1: Look at the leaf electroscope or a vane electroscope that you will be using now.  familiarize  yourself with its responses to static charges: 

Charge the rubber rod with the fur or the wool. THe rod is now negatively charged.

GENTLY bring it in contact with the top of the electroscope. The electroscope is now negatively charged. 

Observe what changes take place in the electroscope. Record your observations:

____________________________________________________________________________________________________________

Step2: Recharge the rubber rod (fur). Bring it near the charged electroscope (NOT TOUCHING) Observe what changes take place to the leaves or the vane. 

Record your observations: 

__________________________________________________________________________________________________________________

Step3: Recharge the electroscope with a negative charge (step1) from the rubber rod (and fur) (REPEAT step1 ABOVE).

Charge (positively) the glass rod with silk and bring it near the top of the negatively charged electroscope (NOT TOUCHING). 

Observe the electroscope deflections as the charged rod is moved close to and away from the electroscope. record your observations :

__________________________________________________________________________________________________

Explain what happened : _________________________________________________________________

Step4: Discharge the electroscope by momentarily touching the top of it with your finger. Make sure the legs are back to their rest position.

Charge the plastic wrap or acrylic rod with a piece of silk (we don't know the charge, you will find out).

Touch the plastic material to the top of the electroscope to charge it.  (it is either negatively charged or positively charges).

Set the plastic material   aside. Charge negatively the rubber rod with the fur. 

bring it near to the electroscope (NOT TOUCHING)  while observing the deflections of the leaves or vane. 

Record your observations. (are the leaves moving a part or getting together ?) 

____________________________________________________________________________________________

So the acrylic rod rubbed by the silk is negative or positive ? (think !  and get it right for full credits)

______________________________________________________________________________________________________

PARTIV : Positively charging a pith ball

Step1: Uncharge the electroscope by touching it. Place a Leyden jar beside the electroscope.

Step2: Charge one of the rods by rubbing it and gently touch the electroscope to charge it.  

Repeat the procedure again and again to place a fair amount of charge and to cause a large deflection

Note the angle of deflection : __________________ (use a protractor)

Step3: Discharge the electroscope by touching the top with your finger. Use the clip wire to attach the top of the electroscope to the top of the leyden jar 

(see figure above ). Note that the leyden jar is not grounded (not connecting to the ground, charges can be trapped in it). DO NOT TOUCH THE

LEYDEN JAR .  Repeat STEP 2 (above) and find out if there is any difference in the ability of the electroscope to be charged? 

Observations : ________________________________________________________________________________

PARTV : CHARGING AN ELECTROSCOPE BY INDUCTION

Step1: Uncharge the electroscope. Charge one of the rod (positively or negatively). Bring the rod  near the electroscope within 1-2cm. 

NOT TOUCHING the electroscope. Observe the leaves or vane. Record your observation 

___________________________________________________________________________________________________________

Step2: READ THE PARAGRAPH FIRST. THE electroscope is uncharged, leaves are at rest. 

BRING  the charged rod NEAR the electroscope. DO NOT TOUCH IT with the rod. With the rod near the electroscope, touch QUICKLY the top of the

electroscope with a finger. Remove quicly your finger AND remove the rod. Observe the leaves or vane.

Observations: ____________________________________________________________________________________________

Explain: ______________________________________________________________________________________________

Hint: touching the electroscope is grounding it. You offer charges a path to follow. The charges that flow will be the ones that are repelled by the charged rod (like charges repell). 

The ones that stay are the ones that are attracted (therefore opposite) to the rod ones.

Step3: Following the procedure in part 3, determine the type of charge on the electroscope: Bring a negatively charged rod near the electroscope.

(rub the rubber rod with the fur). See if the leaves move closer or  farther.  

The electroscope is charged ______________________ because _______________________________________.