TEACHER ANSWER KEY Electrostatics Test Study Guide 2015 1.
The study of electric charge that can be collected and held in one place is called Electrostatics.
2. Identify the SI units for the following: Measurement Electric Field Strength (E) Electric force
SI Unit Newton/coulomb (N/C) Newtons (N)
Measurement Potential Difference (voltage) Charge
SI Unit Volts (V) Coulomb (C)
3. What is the charge of an electron? negative 4. When two objects have the same charge, they will ( attract, repel ). 5. When two objects have different charges, they will ( attract, repel ). 6. What charge will you hair have if you rub a balloon on your head and the balloon becomes negatively charged? positive 7. One coulomb of negative charge has how many electrons? 6.24 x 1018 8. The charge on an electron is equal to the charge on a proton. 9. A rod carrying a negative charge is brought near sphere A. If sphere B is then separated from sphere A, what charge will be on sphere B? Negative 10. Balloons attract electrons. You rub your hair with the balloon. The balloon becomes negative and your hair becomes positive. 11. If you bring a negatively charged balloon near an electroscope, the leaves of the electroscope receive a negative charge because of induction. 12. If you have a strong electrical force, the magnitude of the charge is ( small, large ). 13. Which is the example of conduction? A) Rubbing a balloon on your arm B) Walking across a carpeted floor C) Making your hair stand up when you are touching the van de Graaf generator. D) Moving a soda can with a negatively charged rod. 14. If you have equal numbers of protons and electrons your object has a __ charge. A) Positive B) Negative C) Neutral 15. If you have more protons than electrons, your object will have a _____ charge. A) Positive
B) Negative
C) Neutral
16. If you have more electrons than protons, your object will have a _____ charge. A) Positive B) Negative C) Neutral 17. In a good insulator, electrons A) do not exist. B) are free to move around.
C) are tightly bound in place.
18. Why is metal, such as copper, used to ground buildings? Because it is a good conductor 19. Electric charges are conserved. What does that mean? They are not created nor destroyed. 20. What happens when you rub 2 objects together and create a static charge? Electrons are transferred from one object to another. 21. When 2 charges are moved further apart so their distance is 5 times greater, the force between them is 25 times smaller. 22. If you triple the charge of one object, what will happen to the force? You triple the force. 23. Which of the following is an example of induction? A) Walking across a carpeted floor B) Rubbing a balloon on your arm C) Making your hair stand up when you are touching the van de Graaf generator. D) Moving a soda can with a negatively charged rod. 24. When drawing electron field lines, the arrows always point toward ( positive, negative ) objects and away from ( positive, negative )
objects.
25. When an object is connected to the earth it is grounded. 26. If a charged object is brought closer to the knob of an electroscope, the force will ( increase, decrease ) 27. Electric forces are ( directly, inversely ) proportional to charge and ( directly, inversely ) proportional to the distance. 28. Attractive electric field lines ( curve, are straight lines ) from one charged object ( towards, away from ) the second charged object. 29. In your lab, when two pieces of tape were pulled from the surface, the pieces of tape repelled one another because A) They were oppositely charged B) they became statically charged. C) they were conducting electricity 30. The reason a charged balloon will stick to a wall is that A) electrons transfer back and forth between the wall and the balloon. B) induced opposite charges in the wall attract the balloon. 31. Object A is rubbed against object B and object B becomes positively charged. Electrons were transferred from object ( A, B ) to object ( A, B ).
32. What causes bits of paper to be attracted to a charged plastic comb? Electric charge 33. If I want to increase Electric Field strength, I would have to ( increase, decrease ) the charge? 34. Using the diagram to the right, which of the objects is negatively charged? B
35. The diagram below shows particles that have ( opposite, the same ) charges.
36. The diagram below shows two charges that are ( attracting, repelling )
37. Use the diagram below:
Which charge has the greatest magnitude? __F__ Which charge has the weakest magnitude? __G__
38. The parallel lines shown below are ( oppositely charged, have the same charge, are neutral ).
39. Convert 15 µC to Coulombs. 15 x 10-6 C
Use the following equations to answer Questions (40 – 45)
K q1 q 2 F d2 E
d
F |q|
K q1 q 2 F V
W q
F d2 K q1
q2
K 9.0 x109
V Ed
e- = 1.6 x 10-19
40. Two points on a cloud are both charged with +2 C. They are separated by a distance of 900 m. What is the force acting between these two points?
F
K q1 q 2 d2
(9 x109 ) (2) (2) F (900) 2
F 44,444 N
41. The force of attraction between a – 50 μC and + 90 μC charge is 4.5 N. What distance separates these two charges?
K q1 q 2 F
d
d
(9 x10 9 ) (50 x10 6 ) (90 x10 6 ) 4.5
d 3m
42. A 2.5 C charge is 18 m from the second charge, and the force between them is 1.5 N. What is the magnitude of the second charge?
F d2 q2 K q1
q2
q 2 .000000022 C
1.5 (18) 2 (9 x10 9 ) 2.5
q2
486 2.25 x1010
OR 2.2 x 10-8 C OR 22 x 10-9 C
43. A .5 C charge experiences a 2.0 N force when placed at a certain location. What would the electric field (E) at this location be?
E
F |q|
𝐸=
2.0 .5
E = 4.0 N/C 44. An electron in a TV picture tube passes through a potential difference of 16,500 V. How much work is done on the electron as it passes through the potential difference?
V
W q
16,500
W 1.6 x 10 - 19
1.6 x 10 -19 16,500
W 1.6 x 10 -19 -19 1.6 x 10
W = 2.64 x 10-15J 45. An electron in a TV tube moves 30 cm through an electric field of 500 N/C. How much potential difference is created?
V Ed
V 500 .30
V 150V
