Section 201 Electric Charge and Static Electricity Review and Reinforce
Static Electricity Review
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17. Which of the following charging methods work without always touching the object to be charged to the object used to charge it? Choose all that apply.
| a. charging by friction | b. charging by contact | c. charging by consecration |
Respond: C
In charging by consecration, a charged object is brought virtually an object without touching it. The presence of the charge object induces electron motility and a polarization of the object. And so conducting pathway to ground is established and electron movement occurs between the object and the ground. During the process, the charged object is never touched to the object being charged.
eighteen. Which of the post-obit charging methods result in charging an object opposite to the charge on the object used to charge it? Choose all that apply.
| a. charging by friction | b. charging by contact | c. charging past consecration |
Respond: AC
In charging by friction, the 2 objects being rubbed acquire opposite types of accuse as electrons are transferred betwixt objects.
In charging by contact, both objects acquire the same type of charge.
In charging by induction (as described in the answer to Question #17), the objects acquire the reverse type of accuse.
19. Which of the following statements are true statements virtually electrical force? Choose all that apply.
- Electric forcefulness is a contact strength.
- Electrical forces can only act betwixt charged objects - either like-charged or oppositely-charged.
- Electric forces between two charged objects increases with increasing separation altitude.
- Electric forces betwixt two charged objects increases with increasing quantity of charge on the objects.
- If object A attracts object B with an electric force, then the attractive force must exist common - i.east., object B likewise attracts object A with the same force.
- A doubling of the quantity of charge on one of the objects results in a doubling of the electric force.
- A tripling of the quantity of accuse on both of the objects results in an increase in the electric force past a gene of vi.
- A doubling of the separation distance between two point charges results in a quadrupling of the electric forcefulness.
- A tripling of the separation distance betwixt 2 point charges results in an electric force which is 1-sixth of the original value.
Answer: DEF
a. Electric force is a non-contact forcefulness (or field force); information technology can act over separation distances even when the objects do not touch on.
b. An electrical attraction can even occur between a charged object and a neutral object. The neutral object is first polarized and so the allure can occur.
c. Every bit separation distance increases, the electric force decreases; there is an inverse relationship.
d. Every bit the charge on any of the 2 objects increases, the electrical force increases; there is a directly relationship.
e. Forces - even electric forces - come in pairs. For every action, there is an equal and opposite reaction force. Indeed, to say that "object A attracts object B" is to automatically infer that object B besides attracts object A.
f. Whatever alteration is in made of the charge, the same alteration is fabricated of the electrical force. Doubling the charge will double the force.
m. Whatever alteration is in made of the charge, the same amending is made of the electric forcefulness. Tripling the accuse will triple the force; tripling the other accuse will triple the force once more. Tripling the force (x3) two times will have the net effect of increasing the force by a cistron of ix (non 6).
h. Strength is inversely proportional to the square of the distance. Whatever alteration is fabricated of the distance, the inverse square alteration is made of the force. And so increasing distance by a factor of two (doubling it) will decrease force by a factor of 4.
i. Force is inversely proportional to the foursquare of the distance. Whatever alteration is made of the altitude, the changed foursquare alteration is made of the strength. Then increasing distance by a gene of 2 (doubling it) volition decrease force by a cistron of 9 (3^2).
20. Which of the post-obit statements are truthful statements nigh electrical field? Choose all that apply.
- The electrical field strength created by object A is dependent upon the separation altitude from object A.
- The electric field forcefulness created by object A is dependent upon the accuse on object A.
- The electric field strength created past object A is dependent upon the accuse of the test object used to measure the strength of the field.
- The electric field strength nigh charged Object A is the force per charge experienced by a exam accuse placed at some location about Object A.
- As the distance from Object A is doubled, the electric field strength created by object A increases past a factor of 4.
- As the charge of Object A is doubled, the electric field forcefulness created past object A increases by a factor of 2.
- As the charge of Object A is doubled and the altitude from object A is doubled, the electric field strength created by object A decreases past a gene of two.
- Object B is used to exam the electric field strength about Object A; as the charge of Object B is doubled, the force which it experiences is doubled simply the electric field force remains the same.
- Object B is used to exam the electric field forcefulness about Object A; as the separation distance between Object A and Object B is doubled, the force which information technology experiences decreases past a factor of 4 merely the electric field strength remains the aforementioned.
- The electric field force inside of a closed conducting object (eastward.grand., inside the sphere of the Van de Graaff generator) is aught.
- For irregularly shaped objects, the electrical field strength is greatest effectually points of highest curvature.
- The electric field is a vector which points in the management which a positive exam charge would be accelerated.
- Electric fields are directed inwards in regions effectually negatively-charged objects and outwards in regions around positively-charged objects.
- Units on electric field are Newtons/Coulomb (N/C).
Answer: ABDFGHJKLMN
a. True The Eastward vector depends upon ii factors - the accuse of the object creating the field and the separation distance from that accuse.
b. TRUE The E vector depends upon two factors - the charge of the object creating the field and the separation altitude from that accuse.
c. Faux An object tin can be used to measure the strength of an electric field; such an object is called a test accuse. The test accuse encounters an electric force. The electric field is the ratio of the force divided by the accuse on the test charge. If the quantity of charge on the test charge is increased, the strength is increased proportionately but the ratio remains the aforementioned.
d. TRUE An object can be used to measure the forcefulness of an electrical field; such an object is called a test charge. The test charge encounters an electric force. The electric field is the ratio of the force divided by the charge on the examination charge.
eastward. FALSE The electrical field strength is inversely proportional to the foursquare of the distance of separation from the accuse. If the altitude is increased by a cistron of 2, and then the East is decreased by a gene of 4.
f. Truthful The electrical field strength is directly proportional to the quantity of accuse on the object which creates the field. Doubling the charge (Q) will double the electric field strength.
yard. True The electric field strength is directly proportional to the quantity of accuse on the object which creates the field and inversely proportional to the square of the distance of separation from that accuse. Doubling the charge will take the effect of increasing the E by a factor of 2; doubling the altitude will accept the effect of decreasing the E by a factor of 4. The combined effect of these two factors will result in decreasing the E past a factor of 2.
h. TRUE The electric field force (Due east) created past object A does not depend upon the charge on the object used to examination information technology. The electric field force (F) would be doubled by the doubling of the accuse. But the electrical field force (E) is the forcefulness per charge - twice the force on twice the accuse yields the same electrical field strength.
i. FALSE The electric field strength created by object A does depend on how far from object A that the examination charge is. Twice the separation altitude means one-fourth the electric forcefulness (the inverse square police) and therefore one-fourth of the electric field.
j. True This is a unique property of the electric field inside a closed conductor.
chiliad. TRUE This is another unique property of the electric field. This belongings explains how lightning rods work. Being pointed, the electric field strength is large around the points (parts of highest curvature).
fifty. Truthful This is the customary convention used to define the direction of the electric field around any charged object.
m. TRUE Because electrical field direction is defined every bit the direction which a positively-charged object would advance, the direction would exist toward negatively charged objects (+ test charges are attracted) and away from positively-charged objects (+ examination charges are repelled).
n. True Since electric field is the force per charge exerted upon a test accuse, the units would be strength units per accuse units - Newtons/Coulomb.
21. Which of the post-obit statements are true statements well-nigh lightning rods? Choose all that utilize.
- Lightning rods are placed on homes to reduce the risk of lightning harm to a dwelling.
- Whatsoever metal object which is placed on the roof of a habitation and grounded past an appropriate conducting pathway tin serve as a lightning rod.
- Most lightning rods are pointed every bit a decorative characteristic.
- To be totally effective, a lightning rod must stretch loftier into the sky and draw accuse from the everyman clouds by the method of contact.
- Lightning rods are capable of reducing the excess charge buildup in clouds, a characteristic of dangerous thunderstorms.
- Accuse is incapable of passing from clouds to a lightning rods since the air betwixt the clouds and the lightning rod has an insulating effect.
- The electric field strength about the points of lightning rods are very high.
Answer: AG
a. TRUE The role of lightning rods is to divert charge effectually your dwelling house to the basis in the result of a possible lightning strike.
b. Fake If the lightning rod does non have the feature protrusion up into the air above the building it protects, then it might fail to do what it does best - divert charge around the edifice and preventing it from existence conducted through the home.
c. False Lightning rods are pointed considering the electric field around a sharply curved object is loftier and serves to ionize air around it; this provides a conducting pathway from the cloud to the ground. The pathway allows accuse to slowly flow between cloud and basis, thus preventing a sudden lightning discharge. In more recent years, scientists have plant that a blunt tip on the lightning round provides and equal if not greater measure of protection.
d. FALSE Lightning rods do not need to contact the clouds to discharge them. The strong electric fields around the points serves to turn air from an insulator to a conductor (by ionizing particles in the air). This provides a conducting pathway betwixt the cloud and the lightning rod.
east. FALSE This argument is a good description of the classical dissipation theory of lightning rods. Information technology was once believed (starting time with Ben Frnaklin) that lightning rods served to dissipate or remove electrostatic charge buildup in clouds past removing the charge gradually over time. Scientists generally agree that that dissipation theory is non an authentic view of the role of lightning rods. It is believed that lightning rods serve to divert electrostatic charge around a dwelling during a lightning strike.
f. Fake If this were true, then at that place wouldn't be whatever lightning strikes. The office of the lightning rod is to actually make the pathway between the deject and the ground more than conductive by ionizing the air around the rod and providing a more conductive path from cloud to footing through the lightning rod.
g. True This explains why lightning rods are oftentimes pointed. Though as discussed in more than detail in c. above, blunt-tipped lighning rods take been constitute to provide equal or even greater protection as pointed-tip lightning rods.
22. Charged balloons are used to induce a charge upon neutral metal pop cans. Identify the type of excess accuse which would be present on cans K, H, I, J, Yard, L, M, North and P as shown in the diagrams below.
a. positive
b. negative
c. neutral
Diagram Type of Accuse on... I.
G: positive (A) H: negative (B)
II.
I: negative (B) J: positive (A)
Ii.
K: positive (A) L: negative (B)
M: positive (A)
4.
Northward: negative (B) V.
P: neutral (C)
Reply: See table in a higher place.
I. The presence of the negatively-charged balloon repels electrons which are present in can G. Many of these electrons motility into can H. This leaves can G charged positively (information technology lost electrons) and can H charged negatively (it gained electrons).
2. The presence of the negatively-charged airship next to can J repels electrons which are nowadays in can J. Many of these electrons move into can I. Similarly, the presence of the positively-charged balloon side by side to tin can I will attract electrons present in both cans. This combined effect leaves can J to become charged positively (information technology lost electrons) and can I to become charged negatively (it gained electrons).
Three. The presence of negatively-charged balloons on each cease of the collection of cans causes electrons to be repelled from the balloons. Many electrons leave the 2 cans on the ends and enter the tin can in the middle in order to distant themselves from the balloons. This leaves Can L charged negatively (it gained electrons) and Cans K and 1000 charged positively (they lost electrons).
4. The presence of the positively-charged airship will attract electrons towards itself. In that location is a migration of electrons from the ground (hand) towards the balloon. This leaves can N charged negatively.
V. Electrons in tin can P will exist attracted to the positively-charged airship. This will polarize the tin. But unless there is a source of electrons connected to can P, there is no manner for the can to develop an overall charge. The can remains neutral.
23. In diagram 4 of Question #22, the popular tin acquires the charge that information technology does because ___.
- electrons motion from the balloon to the pop tin
- electrons move from the popular can to the balloon
- protons move from the balloon to the pop can
- protons move from the pop tin to the balloon
- electrons move from the pop can to the hand (ground)
- electrons move from the paw (basis) to the pop can
- protons movement from the pop can to the hand (basis)
- protons move from the hand (ground) to the pop can
Answer: F
Whatsoever explanation which involves the movement of protons can be apace ruled out since protons are bound in the nucleus and incapable of moving about during ordinary electrostatic experiments. Electrons cannot movement from the balloon to the pop can (nor vice versa) since at that place is no connecting path between these two objects. Air is a relatively good insulator and prevents the motility of charge between these ii objects. What happens is that electrons in the hand sense the electric pull of the airship and are fatigued towards information technology, entering the popular can and imparting a negative charge to it.
24. A negatively charged balloon will be attracted to a neutral wooden cabinet due to polarization. Which one of the post-obit diagrams best depict why this occurs?
Answer: D
The molecules of the wooden cabinet are neutral (which rules out diagrams A, B and Due east) yet polarized. The molecules polarize in such a way and so as to make its forward side most highly-seasoned to the airship. This means that the positive poles of the wood molecules are nearest the negative charge of the airship. Merely diagram D shows this orientation.
For Questions #25 - #27, identify the blazon of charge on objects A-D based on the electric field lines shown for each configuration of charges.
a. positive
b. negative
c. neutral
| 25.  A is positive | 26.  B is negative |
| 27.  C is positive and D is negative. | |
Respond: Meet diagrams higher up.
The direction of an electric field is the direction which a positively charged test charge would be accelerated. The electric field lines indicate in this same direction. Equally such, electric field lines are always directed away from + charges and towards - charges (or infinity) . From this principle, it can be reasoned that A is positive, B is negative, C is positive and D is negative.
Part B: Diagramming and Assay
28. A neutral conducting sphere is charged by induction using a positively-charged balloon. What will be the charge of the following sphere in pace e if steps a - d are followed? _________
Explain how the object acquires this charge. Prove the type and location of excess charge on the conducting sphere in each stride of the diagram (where appropriate).
Reply: See diagram higher up.
In b., the presence of the positively-charged airship serves to polarize the sphere. Electrons in the sphere are drawn towards the positively-charged balloon. This leaves a separation of accuse in the sphere, with the excess negative accuse on the left and the excess positive accuse on the correct.
In c., the sphere is touched to ground and electrons from the ground are fatigued upwards and into the right side of the sphere. Information technology is the presence of the + charge on the right side of the sphere which attracts these electrons to itself. At this signal the sphere is charged negatively.
In d., this excess negative charge is shown distributed on the left side of the sphere, yet fatigued towards the positively-charged balloon.
In e,. the balloon is pulled away and in that location is a movement of electrons about the sphere so that the excess negative charge is uniformly distributed.
A negatively-charged balloon is held in a higher place (without touching) a neutral electroscope. The presence of the nearby balloon causes the needle of the electroscope to deflect.
a. Draw the location and type of excess charges on the "polarized" neutral electroscope.
b. Explain how the airship has induced the temporary charge upon the electroscope (i.e., describe the direction of electron movement).
Answer: See diagram at right.
The negative balloon repels electrons from the plate to the needle and base. Since like charges are repelled, electrons in the top of the electroscope (the plate) are repelled and forced down to the bottom of the electroscope (the needle and base). This causes the temporary separation of charge or polarization of the electroscope.
[ #17 | #xviii | #19 | #twenty | #21 | #22 | #23 | #24 | #25 | #26 | #27 | #28 | #29 | #30 | #31 | #32]
thirty. Construct electrical field lines around the following configuration of charges. Include at least six lines per charge.
Answer: Meet diagrams above
Electric field lines begin at either infinity or a + charge and are fatigued either to infinity or to - charges. Avoid crossing lines. At the surface of charges, the lines should exist directed radially inwards (for - charges) or radially outwards (for + charges).
31. Utilize an unbroken arrow to show the direction of electron move in the following situation. The arrow should extend from the source of the electrons to the concluding destination of the electrons.
| a. A positively charged balloon is touched to a neutral conducting sphere.  Electrons movement from the sphere to the + balloon. | b. A glass rod is rubbed with a piece of wool. The wool has the greater electron affinity.  Electrons motion from the drinking glass rod to the wool. |
| c. A positively-charged balloon is held near a neutral conducting sphere. The sphere is and then touched on the opposite side.  Electrons move from the manus to the sphere. | d. A negatively-charged rod is held near a neutral conducting sphere. The sphere is touched on the reverse side.  Electrons move from the sphere to the hand. |
Answer: Encounter diagrams above.
In a, c, and d, the movement of electrons is governed by the principles that opposites concenter and similar-charged objects repel. Electrons (beingness negative) are attracted to positively charged objects and repelled by negatively charged objects.
In b, the more electron-loving substance (highest electron affinity) gains the electrons from the object with which it is rubbed.
32. A negatively-charged object creates an electric field which can be measured at diverse locations in the region nearly it. An electric field vector is drawn for bespeak X. Use your understanding of the electric field - distance relationship to describe E vectors for points A - E. (The length of the pointer should exist indicative of the relative strength of the Eastward vector.)
Respond: Run into diagram higher up.
The electric field vector points in the direction which a positive test charge would be accelerated. This would result in a vector directed towards a negatively charged object. Thus all E vectors point towards the negatively-charged object. The Eastward vector is inversely dependent upon square of the altitude. Thus, the points which are further away have the smallest E vectors.
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