1- What is the conclusion of the first video activity(Electric Force vs. Charge)?

Explain your answer by referring tothe graph “Force vs. Charge” that you created in Part H of thefirst video activity. Please insert the data table and the graphside by side and then write your answer underneath.

Viedo Link:https://mediaplayer.pearsoncmg.com/assets/_frames.true/secs-coulomb-force-2-force-vs-charge

Part A

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Assume that the Styrofoam slab and the fur are both initiallyneutral, and that the slab charged negatively after it isrubbed with the fur. Describe what happens.

Mark all the correct statements among those provided below.

Protons move from the fur to the slab.

Protons move from the slab to the fur.

Electrons move from the fur to the slab.

Electrons move from the slab to the fur.

The fur becomes negative after rubbing the slab.

The fur becomes positive after rubbing the slab.

The fur remains neutral after rubbing the slab.

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Since the electrons are the mobile charge carriers, they aretransferred in this case from the fur to the slab. As a result, thefur will have fewer electrons than it began with, thus leaving itpositively charged.

Part B

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After the slab is charged, and the electrophorus is placed onthe slab, the student briefly touches the electrophorus,effectively grounding it. After that, the electrophorus appears tobe charged. By what method is it charged?

Select the best answer from the choices provided.

induction

conduction

rubbing

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Charging by induction means that a charged object (the slab)causes the other one (the electrophorus) to become charged byinfluencing (inducing) the process of charge transfer;however, little or almost no charge transfer occurs directlybetween the charging object and the object being charged.

What, exactly, is happening in this particularcase?

Part C

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As the hand touches the electrophorus, in which direction do theelectrons move?

Select the best answer from the choices provided.

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The electrons move from the electrophorus to the slab.

The electrons move from the hand to the slab.

The electrons move from the hand to the electrophorus.

The electrons move from the slab to the electrophorus.

The electrons move from the slab to the hand.

The electrons move from the electrophorus to the hand.

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The negatively charged slab is pushing the “free” electrons inthe conducting electrophorus away. Before the electrophorus isgrounded, there is no escape path for those electrons.Therefore, the electrophorus is polarized; that is, itstop surface is negative, and the bottom one, the one nearest theslab, is positive. However, the electrophorus remainsneutral until the hand provides a conducting path thatallows some electrons escape from the electrophorus, rendering itpositive.

Part D

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Observe the process by which the grey and the red spheres arecharged using the electrophorus. After each sphere is firstcharged, what are their charges?

Select the best answer from the choices provided.

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The gray sphere has a negative charge and thered sphere has a positive charge.

The gray sphere has a negative charge and thered sphere has a negative charge.

The gray sphere has a positive charge and thered sphere has a positive charge.

The gray sphere has a positive charge and thered sphere has a negative charge.

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The electrophorus becomes less positive once it pulls someelectrons away from the red sphere. However, the electrophorus isreplaced on the slab and recharged by grounding it before itproceeds to charge the grey sphere. This ensures that both spheresinitially have about the same amount of charge.

Since the red sphere is suspended on an insulating handle, andno other objects toch it, we cna assume that its charge remainsconstant throughout the experiment. However, this is not the casefor the gray sphere.

Part E

Part complete

Before we proceed with the quantitative part of this set, let usmake sure that you can see the reading of the electronic balanceclearly on your screen. What is the reading of the scale rightafter the red sphere is first charged, and the electrophorus hasbeen replaced on the slab? Use the “pause” and the“frame-by-frame-advance” buttons to navigate to the appropriatepart in the video.

Select the best answer from the choices provided.

0.000005N0.000005N

0.00005N0.00005N

5N5N

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Note that the scale has been adjusted so that it readsapproximately zero when the only force acting on it is gravity. Asmall difference from zero is frequently observed with sensitivescales.

Part F

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What is the reading of the scale after both spheres have beencharged, and the student is getting ready to bring the hand-heldsphere close to the bottom sphere? Consider the moment when thehand-held sphere is about half-way between the handle of theelectrophorus and the bottom sphere. Use the “pause” and the“frame-by-frame-advance” buttons to navigate to the appropriatepart in the video.

Express your answer in Newtons. Use three significant figures inyour answer.

0.00175

NN

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Now let us see what happens when the charge of the bottom spherebegins to change.

Part G

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The bottom sphere is briefly touched by another conductingsphere of the same size, mounted on an insulating handle. Assumingthat the charge of the bottom sphere is +q+q before it is touchedby the other sphere, what is its charge after it is touched?

Select the best answer from the choices provided.

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−q/2−q/2

−q−q

−2q−2q

+q/2+q/2

+q+q

+2q+2q

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Note that, after each touch of the spheres, the handheld one isbriefly touched by hand—that is, neutralized—through grounding.That means that each subsequent touch would remove half of thecharge from the bottom sphere.

Part H

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We will now try to determine how the magnitude of the Coulombforce between the spheres depends on the charge of the bottomsphere. Now that we understand that the charge of the bottom sphereis halved after each touch, create a graph “force vs. charge of thebottom sphere” using +q+q, +q/2+q/2, +q/4+q/4, etc. as the chargevalues. What is the most reasonable conclusion that can be madefrom the graph about the magnitude of the Coulomb force?

Select the best answer from the choices provided.

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It is inversely proportional to the square of the charge of thebottom sphere.

It is inversely proportional to the charge of the bottomsphere.

It is directly proportional to the square of the charge of thebottom sphere.

It is directly proportional to the charge of the bottomsphere.

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It seems reasonable to assume that the magnitude of the forcewould be also directly proportional to the charge of thetop sphere—in other words, directly proportional tothe product of the charges of the spheres! (Recall thatthe magnitude of the force of gravity between two spherical massesis directly proportional to the product of the masses ofthe spheres.)

Now, let's do one last exercise to make sure you are comfortablewith this idea.

Part I

Part complete

Let us suppose the magnitude of the original Coulomb forcebetween the two charged spheres is FF. In this scenario, a thirdsphere touches the grey sphere and the red sphere multiple times,being grounded each touch. If the grey sphere is touched twice, andthe red sphere is touched three times, what is the magnitude of theCoulomb force between the spheres now?

Select the best answer from the choices provided.

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F/5F/5

F/6F/6

F/8F/8

F/16F/16

F/32F/32

In another DMV-based activity, you will explore (if you haven’talready done that) the dependence of the Coulomb force on thedistance between the spheres.