. You are now ready to use the electrometer to measure potentials. To select the

Question

. You are now ready to use the electrometer to measure potentials. To select the desired range of the meter, press the "Rang" button located on the lower left of the unt. To begin, set the meter to the 30 Volt or the 100 Volt range. The range setting refers to the potential input instance a setting of 30 means that a full scale meter deflection indicates a poten of 30 Volts.) D uired to produce a full scale meter deflection. (For tial of the uring the following measurements adjust the sensitivity electrometer so that the readings are in lie upper two thirds of the scale. Again use the zero button to discharge the Ice Pail. Discharge the two (white an blue) charge producing disks. This can be done by touching the aluminum part the disk to ground (i.e., the outer cylindrical mesh). (You may t temporarily create for charges on the disk by blowing on the plastic neck. The moisture in your breath will produce a leakage path for charge. Do not touch the plastic since grease from your hand will destroy the insulating properties of the plastic. If needed, you can clean the plastic neck with alcohol and/or dry it using a heat lamp.) Check that the charge producers are in fact disch within the ice pail. It will be worthwhile in the following measurements to g yourself by touching the grounded shield. by placing them one at a time Part I: Measurement of Charge 1-1. Rub the two charge producers together (white disk against blue disk) to produce net charge on each. Insert one wand (either blue or white) into the Ice Pail but Record the electrometer reading (sign and do not let it touch the magnitude). The charged object should inserted at least into the lower half of the Ice- Pail. Remove the wand from the Ice-Pail and again record the electrometer reading. Repeat 5 times. Part II: Measurement of Induced Charge Il-1. Discharge the Ice Pail and again insert the charged wand, but now allow it to touch the inside of the Pail for a few seconds before it is removed. Record the electrometer reading after the wand is removed. Discharge the Ice Pail and then touch the object to it again. Record the electrometer reading. Does any charge remain on the object? Recharge the wands by rubbing again, and repeat the procedure 5 times. What conclusion can you draw about the induced charge on he Ice Pail as compared to the charge on the charge producer? Part III: Two Types of Charge III-1. Discharge the Ice Pail and the two charge producers. Rub the two charge producers together and measure the charge on each. Next, discharge each wand touching them to the outer mesh, then repeat procedure 5 times. What is the relationship between these charges? III-2. Rub the rubber rod against the cat's fur. Insert the rubber rod into the ice pail, and note the direction of deflection on the electrometer. Repeat one time. Next, rub a glass rod against the silk, and repeat the measurement procedure.

Explanation / Answer

Hi.

1) This is a very experimental question and can be answered only by you , who is doing the experiment. Basically, there will be no effect in varying the position within the pail. If we get too close to the pail wall, then the ball might get attracted too much and touch the wall and transfer the charge. SO, you wont be going too close to the wall anyway. You will be near the axis of the pail. By lowering the ball into the lower half of the pail, you ensure that the flux lines produced by the ball are all made to pass into the pail and not the open top of the pail.

2) Part 1 and Part 3.

Eventhough it is neutral, when we take the ball near the pail, there is a local concentration of charge in the pail.

The charge that is opposite to the pail charge (hence the same as the ball charge) get concentrated in the farthest point they can be, which are the terminals of the electroscope. Hence, the net effect (as long as the ball is within the pail) is having charged terminals and it is measured.

3) Only part 2 because we let the ball touch.

4)Conductors : Copper, Silver, basically all metallic objects

Insulators: Plastic, Wood, Cotton

Conductors have free electrons, that are not tightly bound to a single atom. Hence they can move freely within the conductor.

Insulators have very tightly bound electrons and offer great resistance to electric fields that are applied across them. Their electrons are not free to move.

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