Lab 2 Electrostatics

neutral

A ____ (unchanged) object has zero total charge, but different regions of a neutral body may have charge.

polarization

A charged object can exert an attractive electric force on an electrically neutral object. This comes about through a process called _____ in which the charged object causes a rearrangement of the charges in the neutral object.

A charged rubber rod was brought near the electroscope. The meter will indicate a voltage. Why?

Although the electrometer is off, the electrometer indicates a voltage because

Purpose:

Electric charges were separated by friction and the interaction of two different kinds of electric charge were explored.

conductors

Electrons can move around easily on metal objects since most metals are good electric _____. If you bring a charged object near a conducting surface, you will cause electrons to move on the _____ even though there is no physical contact.

positive charges remain where they were

Negative charges (electrons) are transferred while...

electric force

Objects that have a net electric charge exert an ____ ____ on other charged objects.

The ball came in contact with the entire glass rod. Now both of them have the same charge. The charged rubber rod was brought near the ball. Q4. Describe what the ball does now. Is the pith ball attracted to or repelled from the rubber rod? Why?

Since they both had the same charge, the pith ball was repelled from the rubber rod because like repels like.

charging by induction

The electroscope is left with a net charge when the rod is removed after removing my finger. Electrons are pulled in from my hand (or pushed out to your hand) by the influence of the charged rod, then become trapped on the electroscope when my finger was removed.

Setup:

The interactions of the two electric charges were explored by rubbing flannel against the rod in order to give the rod a charge. Using a string, the charged rubber rod was hanged. The charged glass rod was then brought near to one end of the rubber rod. The entire recharged rubber rod was rubbed all over the hanging pith ball. A glass rod that has been rubbed with cloth was brought near the same ball without touching. The charged rubber rod was placed near a stream of water and then near the electroscope. While holding the rod near the electroscope, I touched the metal strip inside the cylindrical housing with my finger. The electrometer indicated zero. I removed my finger. And then removed the rod. In another experiment, the plastic plate was rubbed with flannel. The metal disk was placed on top of the plate. The metal disk was discharged by touching it. I then removed my fingers. The disk was discharged again. These steps were repeated until there was a spark.

Coulomb's Law

The magnitude of the electric force depends on the amount of charge on each object and inversely on the square of the distance between the objects

1. The charged rubber rod was hanged by a string. The charged glass rod was brought near to one end of the rubber rod. Q1. Explain what happens. Does the strength of the electrostatic force appear to depend on the distance between the rods?

The negatively charged rubber rod was attracted to the positively charged glass rod, so the rubber rod moved towards the glass rod. The strength of the electrostatic force depends on the distance between the rods. EXPLAIN WHY

2. The entire recharged rubber rod was rubbed all over the hanging pith ball. This caused them to have the same charge. Q2. Is the pith ball attracted to or repelled from the rubber rod? Why?

The pith ball is repelled from the rubber rod because they have the same charge and like repels like.

insulated

The total amount of charge on an electrically isolated, or _____, object does not change.

D. The Electrophorous

This is a plastic square and a metal disk with an insulated handle used to illustrate charging by induction. The plastic square tends to hold on firmly to any charge it acquires.

Analysis: A. Charging by Friction and Electrostatic Forces

Upon rubbing with flannel, the rubber rod was negatively charged, and glass rod was positively charged.

(1) Positive (protons) (2) Negative (electrons)

What are the two kinds of electric charge we find in nature?

The glass rod becomes positively charged and the cloth becomes negatively charged. A glass rod is willing to give up electrons to the cloth.

What will happen when a glass rod is rubbed with a cloth?

Since the rubber rod does not want to give up its electrons to the cloth, electrons transfer from the cloth to the rubber. This makes the rubber rod negatively charged.

When a rubber rod is rubbed with cloth, where will the electrons transfer to?

A glass rod that has been rubbed with cloth was brought near the same ball without touching. Q3. Is the pith ball attracted to or repelled from the glass rod? Why?

When the glass rod was rubbed with the cloth, it made it positively charged. Since the rubber rod was negative and since it transferred its charge to the pith ball, the pith ball was also negative. The negatively charged pith ball was thus attracted to the positively charged glass rod because opposites attract.

when there is an imbalance between the number of protons and the number of electrons

When will an object be electrically charged?

They have equal number of protons and electrons

Why are atoms electrically neutral or uncharged?

Electrostatics

____ is the study of the forces between charges that are static (not moving).

negative charge

more electrons than protons

positive charge

more protons than electrons

Equipment:

•Stand and one pith ball •Rubber and glass rods, silk, flannel and fur •Electroscope, with PASCO Basic Electrometer (ES-9078) in place of gold foil •Electrophorus •Neon bulb •Rod holder and string