Skills Worksheet Concept Review Section Electric Charge and Force
Static Electricity Review
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17. Which of the following charging methods work without e'er touching the object to be charged to the object used to accuse it? Choose all that apply.
| a. charging by friction | b. charging by contact | c. charging by induction |
Answer: C
In charging by induction, a charged object is brought near an object without touching it. The presence of the charge object induces electron move and a polarization of the object. Then conducting pathway to ground is established and electron motility occurs between the object and the ground. During the process, the charged object is never touched to the object beingness charged.
18. Which of the following charging methods upshot in charging an object reverse to the charge on the object used to charge information technology? Choose all that use.
| a. charging by friction | b. charging by contact | c. charging by induction |
Respond: AC
In charging by friction, the two objects being rubbed learn opposite types of accuse as electrons are transferred between 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 opposite type of charge.
19. Which of the following statements are true statements virtually electric force? Choose all that use.
- Electric force is a contact force.
- Electrical forces can merely human action between charged objects - either like-charged or oppositely-charged.
- Electric forces between two charged objects increases with increasing separation distance.
- Electric forces betwixt 2 charged objects increases with increasing quantity of charge on the objects.
- If object A attracts object B with an electric force, then the bonny strength must be mutual - i.e., object B too attracts object A with the same strength.
- A doubling of the quantity of charge on i of the objects results in a doubling of the electric force.
- A tripling of the quantity of charge on both of the objects results in an increment in the electric forcefulness by a cistron of 6.
- A doubling of the separation distance between ii point charges results in a quadrupling of the electric force.
- A tripling of the separation altitude between 2 betoken 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 tin act over separation distances even when the objects do not touch.
b. An electrical attraction can even occur between a charged object and a neutral object. The neutral object is first polarized and then the attraction tin occur.
c. As separation distance increases, the electrical force decreases; there is an inverse human relationship.
d. As the accuse on whatever of the ii objects increases, the electric forcefulness increases; there is a straight relationship.
e. Forces - even electrical forces - come in pairs. For every action, at that place is an equal and opposite reaction force. Indeed, to say that "object A attracts object B" is to automatically infer that object B also attracts object A.
f. Whatever alteration is in made of the charge, the same alteration is made of the electric force. Doubling the charge will double the strength.
yard. Whatever alteration is in made of the accuse, the same alteration is fabricated of the electrical force. Tripling the accuse will triple the strength; tripling the other charge will triple the force over again. Tripling the force (x3) two times will have the net effect of increasing the force past a factor of 9 (not 6).
h. Forcefulness is inversely proportional to the square of the altitude. Whatever alteration is made of the distance, the inverse square alteration is made of the forcefulness. So increasing altitude by a factor of 2 (doubling it) will subtract forcefulness by a factor of 4.
i. Force is inversely proportional to the square of the altitude. Whatever amending is made of the distance, the inverse square alteration is made of the strength. Then increasing distance by a cistron of 2 (doubling it) will subtract force past a factor of 9 (3^2).
xx. Which of the following statements are true statements nearly electrical field? Choose all that apply.
- The electric field strength created by object A is dependent upon the separation distance from object A.
- The electric field force created past object A is dependent upon the accuse on object A.
- The electrical field strength created by object A is dependent upon the charge of the test object used to mensurate the strength of the field.
- The electrical field strength about charged Object A is the force per charge experienced past a test accuse placed at some location about Object A.
- As the distance from Object A is doubled, the electric field force created by object A increases by a factor of four.
- As the charge of Object A is doubled, the electric field forcefulness created past object A increases past a factor of 2.
- As the charge of Object A is doubled and the distance from object A is doubled, the electric field force created past object A decreases by a cistron of 2.
- Object B is used to test the electric field force about Object A; as the charge of Object B is doubled, the strength which it experiences is doubled but the electric field force remains the same.
- Object B is used to test the electric field strength nearly Object A; equally the separation distance between Object A and Object B is doubled, the force which information technology experiences decreases by a factor of four but the electric field strength remains the same.
- The electrical field strength inside of a closed conducting object (e.g., inside the sphere of the Van de Graaff generator) is nix.
- For irregularly shaped objects, the electric field strength is greatest effectually points of highest curvature.
- The electric field is a vector which points in the direction which a positive test accuse would be accelerated.
- Electrical fields are directed in in regions around negatively-charged objects and outwards in regions around positively-charged objects.
- Units on electric field are Newtons/Coulomb (Northward/C).
Reply: ABDFGHJKLMN
a. TRUE The Eastward vector depends upon two factors - the charge of the object creating the field and the separation altitude from that charge.
b. TRUE The E vector depends upon two factors - the charge of the object creating the field and the separation distance from that charge.
c. Faux An object can be used to mensurate the strength of an electric field; such an object is called a exam charge. The test charge encounters an electric force. The electric field is the ratio of the force divided by the charge on the test accuse. If the quantity of accuse on the examination charge is increased, the force is increased proportionately merely the ratio remains the same.
d. TRUE An object tin can be used to measure out the strength of an electric field; such an object is called a test charge. The exam charge encounters an electric forcefulness. The electric field is the ratio of the forcefulness divided by the charge on the exam charge.
e. FALSE The electric field strength is inversely proportional to the foursquare of the distance of separation from the accuse. If the distance is increased by a factor of ii, then the East is decreased by a cistron of 4.
f. TRUE The electric field forcefulness is directly proportional to the quantity of charge on the object which creates the field. Doubling the charge (Q) will double the electric field force.
m. True The electric field forcefulness is directly proportional to the quantity of charge on the object which creates the field and inversely proportional to the square of the distance of separation from that charge. Doubling the charge will take the consequence of increasing the E by a factor of 2; doubling the altitude volition accept the effect of decreasing the E by a factor of iv. The combined issue of these 2 factors will result in decreasing the E by a factor of 2.
h. TRUE The electric field strength (Due east) created by object A does not depend upon the charge on the object used to test it. The electric field force (F) would be doubled by the doubling of the charge. But the electrical field forcefulness (E) is the forcefulness per accuse - twice the forcefulness on twice the charge yields the aforementioned electric field strength.
i. Fake The electric field forcefulness created past object A does depend on how far from object A that the examination charge is. Twice the separation distance means one-4th the electrical force (the changed square law) and therefore one-fourth of the electrical field.
j. Truthful This is a unique property of the electric field within a airtight conductor.
thousand. TRUE This is another unique property of the electrical field. This property explains how lightning rods work. Existence pointed, the electric field force is big effectually the points (parts of highest curvature).
fifty. Truthful This is the customary convention used to define the management of the electric field around any charged object.
1000. Truthful Because electric field management is defined every bit the direction which a positively-charged object would advance, the direction would be toward negatively charged objects (+ test charges are attracted) and abroad from positively-charged objects (+ examination charges are repelled).
due north. Truthful Since electric field is the forcefulness per charge exerted upon a test charge, the units would be force units per charge units - Newtons/Coulomb.
21. Which of the following statements are true statements about lightning rods? Choose all that utilise.
- Lightning rods are placed on homes to reduce the risk of lightning damage to a domicile.
- Any metallic object which is placed on the roof of a home and grounded past an advisable conducting pathway can serve as a lightning rod.
- Virtually lightning rods are pointed as a decorative feature.
- To be totally effective, a lightning rod must stretch high into the heaven and draw charge from the lowest clouds by the method of contact.
- Lightning rods are capable of reducing the excess charge buildup in clouds, a characteristic of dangerous thunderstorms.
- Charge is incapable of passing from clouds to a lightning rods since the air between 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 accuse effectually your home to the footing in the issue of a possible lightning strike.
b. False If the lightning rod does not accept the characteristic protrusion up into the air above the edifice it protects, then it might fail to practice what information technology does best - divert accuse around the building and preventing it from being conducted through the home.
c. False Lightning rods are pointed because the electric field around a sharply curved object is high and serves to ionize air around it; this provides a conducting pathway from the deject to the ground. The pathway allows charge to slowly flow between cloud and ground, thus preventing a sudden lightning discharge. In more contempo years, scientists have constitute that a blunt tip on the lightning circular provides and equal if not greater measure of protection.
d. Fake Lightning rods exercise not need to contact the clouds to belch them. The strong electric fields around the points serves to plow air from an insulator to a conductor (past ionizing particles in the air). This provides a conducting pathway between the cloud and the lightning rod.
e. FALSE This statement is a practiced description of the classical dissipation theory of lightning rods. It was once believed (beginning with Ben Frnaklin) that lightning rods served to misemploy or remove electrostatic accuse buildup in clouds by removing the accuse gradually over time. Scientists generally concord that that dissipation theory is not an accurate view of the role of lightning rods. It is believed that lightning rods serve to divert electrostatic charge effectually a home during a lightning strike.
f. FALSE If this were truthful, and then at that place wouldn't be any lightning strikes. The role of the lightning rod is to really make the pathway between the cloud and the basis more conductive past ionizing the air around the rod and providing a more conductive path from cloud to basis through the lightning rod.
g. TRUE This explains why lightning rods are often pointed. Though as discussed in more than detail in c. above, blunt-tipped lighning rods have been found to provide equal or fifty-fifty greater protection as pointed-tip lightning rods.
22. Charged balloons are used to induce a accuse upon neutral metallic pop cans. Identify the blazon of backlog charge which would be nowadays on cans 1000, H, I, J, K, L, M, Northward 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)
2.
I: negative (B) J: positive (A)
Ii.
K: positive (A) Fifty: negative (B)
Chiliad: positive (A)
IV.
N: negative (B) V.
P: neutral (C)
Answer: Run into table higher up.
I. The presence of the negatively-charged airship repels electrons which are present in can K. Many of these electrons movement into tin can H. This leaves tin can M charged positively (it lost electrons) and tin can H charged negatively (it gained electrons).
2. The presence of the negatively-charged balloon next to tin J repels electrons which are present in tin J. Many of these electrons move into tin I. Similarly, the presence of the positively-charged balloon next to tin can I will concenter electrons present in both cans. This combined effect leaves can J to become charged positively (it lost electrons) and tin I to become charged negatively (it gained electrons).
3. The presence of negatively-charged balloons on each finish of the collection of cans causes electrons to be repelled from the balloons. Many electrons leave the two cans on the ends and enter the can in the eye in order to afar themselves from the balloons. This leaves Tin 50 charged negatively (it gained electrons) and Cans K and G charged positively (they lost electrons).
Iv. The presence of the positively-charged balloon volition attract electrons towards itself. There is a migration of electrons from the ground (hand) towards the balloon. This leaves can N charged negatively.
Five. Electrons in can P will be attracted to the positively-charged balloon. This will polarize the can. But unless there is a source of electrons continued to tin P, there is no style for the can to develop an overall charge. The tin can remains neutral.
23. In diagram Four of Question #22, the popular can acquires the accuse that information technology does because ___.
- electrons move from the balloon to the pop tin
- electrons move from the pop tin can to the balloon
- protons move from the balloon to the pop can
- protons movement from the pop tin to the balloon
- electrons motility from the popular tin can to the mitt (ground)
- electrons motion from the hand (ground) to the pop can
- protons move from the popular can to the hand (basis)
- protons move from the mitt (ground) to the pop tin can
Answer: F
Any explanation which involves the movement of protons tin can be chop-chop ruled out since protons are bound in the nucleus and incapable of moving well-nigh during ordinary electrostatic experiments. Electrons cannot movement from the balloon to the pop can (nor vice versa) since there is no connecting path between these two objects. Air is a relatively good insulator and prevents the movement of accuse betwixt these ii objects. What happens is that electrons in the hand sense the electric pull of the balloon and are fatigued towards it, entering the pop can and imparting a negative charge to it.
24. A negatively charged balloon volition exist attracted to a neutral wooden cabinet due to polarization. Which one of the following 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 equally to brand its forward side well-nigh highly-seasoned to the balloon. This means that the positive poles of the wood molecules are nearest the negative accuse of the balloon. Only diagram D shows this orientation.
For Questions #25 - #27, identify the type 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. | |
Answer: See diagrams above.
The direction of an electric field is the direction which a positively charged test charge would be accelerated. The electric field lines signal in this aforementioned direction. As such, electric field lines are always directed away from + charges and towards - charges (or infinity) . From this principle, information technology can be reasoned that A is positive, B is negative, C is positive and D is negative.
Part B: Diagramming and Analysis
28. A neutral conducting sphere is charged by induction using a positively-charged balloon. What volition be the charge of the following sphere in step e if steps a - d are followed? _________
Explicate how the object acquires this charge. Show the type and location of excess accuse on the conducting sphere in each step of the diagram (where appropriate).
Answer: See diagram above.
In b., the presence of the positively-charged balloon 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 charge on the left and the excess positive charge on the right.
In c., the sphere is touched to ground and electrons from the ground are drawn upwards and into the correct side of the sphere. It is the presence of the + charge on the right side of the sphere which attracts these electrons to itself. At this point the sphere is charged negatively.
In d., this excess negative charge is shown distributed on the left side of the sphere, still drawn towards the positively-charged balloon.
In eastward,. the balloon is pulled away and there is a motility of electrons about the sphere then that the backlog negative charge is uniformly distributed.
A negatively-charged balloon is held above (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 balloon 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 meridian of the electroscope (the plate) are repelled and forced downwards to the bottom of the electroscope (the needle and base). This causes the temporary separation of charge or polarization of the electroscope.
[ #17 | #xviii | #nineteen | #twenty | #21 | #22 | #23 | #24 | #25 | #26 | #27 | #28 | #29 | #xxx | #31 | #32]
30. Construct electric field lines around the following configuration of charges. Include at least vi lines per charge.
Answer: Run across diagrams above
Electrical field lines begin at either infinity or a + charge and are drawn either to infinity or to - charges. Avoid crossing lines. At the surface of charges, the lines should be directed radially in (for - charges) or radially outwards (for + charges).
31. Use an unbroken arrow to show the management of electron movement in the post-obit situation. The pointer should extend from the source of the electrons to the final destination of the electrons.
| a. A positively charged airship is touched to a neutral conducting sphere.  Electrons move from the sphere to the + airship. | b. A drinking glass rod is rubbed with a piece of wool. The wool has the greater electron analogousness.  Electrons move from the glass rod to the wool. |
| c. A positively-charged airship is held near a neutral conducting sphere. The sphere is and then touched on the opposite side.  Electrons move from the hand to the sphere. | d. A negatively-charged rod is held near a neutral conducting sphere. The sphere is touched on the opposite side.  Electrons movement from the sphere to the hand. |
Answer: See diagrams above.
In a, c, and d, the movement of electrons is governed by the principles that opposites attract and like-charged objects repel. Electrons (existence negative) are attracted to positively charged objects and repelled past 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 electrical field which can be measured at diverse locations in the region nearly information technology. An electric field vector is drawn for bespeak X. Employ your understanding of the electric field - distance human relationship to draw E vectors for points A - E. (The length of the pointer should be indicative of the relative forcefulness of the Eastward vector.)
Answer: Meet diagram to a higher place.
The electric field vector points in the direction which a positive exam charge would be accelerated. This would result in a vector directed towards a negatively charged object. Thus all East vectors indicate towards the negatively-charged object. The Due east vector is inversely dependent upon foursquare of the altitude. Thus, the points which are further away accept the smallest E vectors.
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