Download 16 Electrostatics WS 08 [v6.0]

Honors Physics
Worksheet
Chapter 16 Electrostatics
N •m 2
Use k= 9.0 x 10
, g= 9.80 m /s2 and e= 1.60 x 10−19 C as needed.
2
C
9
1. Suppose a rubber rod is rubbed with cat fur.
(a) The rod acquires a€(negative, positive)
charge. (Answer: negative)
€
(b) What subatomic particle was transferred between the rod and the fur? (Answer: electron)
€
(c) The subatomic particle moved from (the fur to the rod, the rod to the fur).
(Answer: the fur to the rod)
2. Suppose a glass rod is rubbed with silk.
(a) The rod acquires a (negative, positive) charge. (Answer: positive)
(b) The silk acquires a (negative, positive) charge. (Answer: negative)
3. A pith ball is suspended by a thread. The ball is grounded by touching it and then a positively
charged rod is brought near the pith ball.
(a) The pith ball is (attracted to the rod, repelled from the rod, neither attracted to nor repelled
from the rod). (Answer: attracted to the rod)
(b) What is the net charge on the pith ball when the rod is in the vicinity of the ball?
(Answer: the pith ball is uncharged)
(c) A (negative, positive) charge is induced on the side of the pith ball closest to the rod.
(Answer: negative)
(d) If the rod touches the pith ball then the net charge on the pith ball will be (zero, negative,
positive) (Answer: positive)
(e) After the rod touches the ball, the ball will be (attracted to the rod, repelled from the rod,
neither attracted to nor repelled from the rod). (Answer: repelled from the rod)
4. A pith ball is suspended by a thread. The ball is grounded by touching it. A rubber rod is
rubbed with cat fur and is brought into contact with the ball. A glass rod that was rubbed with
silk is now brought near the pith ball. The ball will be (attracted to the glass rod, repelled from
the glass rod, neither attracted to nor repelled from the glass rod).
(Answer: attracted to the glass rod)
5. Fill in the chart that summarizes properties of the parts of an atom.
Particle
Mass
Charge
Proton
1
+1
Fundamental or made
of smaller parts
Location
Fundamental or made
of smaller parts
Location
Neutron
€
Electron
Answer:
Particle
Mass
Charge
Proton
1
+1
Neutron Slightly more
than 1
€
Electron Slightly more
than zero
6. (a)
(b)
(c)
(d)
0
−1
Made of smaller
parts (quarks)
Made of smaller
parts (quarks)
Fundamental
Nucleus
Nucleus
Outside
nucleus
What force holds the particles of the nucleus together? (Answer: strong nuclear force)
What force binds electrons
€ to the nucleus? (Answer: electromagnetic force)
What force is associated with radioactive decay? (Answer: weak nuclear force)
What force exists between any two masses? (Answer: gravitational force)
7. ____ is a force that involves charges in motion. (Answer: Magnetism)
8. An isotope of chlorine has atomic number 17 and mass number 36.
(a) How many protons are there in a chlorine atom? (Answer: 17)
(b) How many electrons are there in a neutral chlorine atom? (Answer: 17)
(c) How many neutrons are there in an atom of this isotope? (Answer: 19)
−19
(d) The magnitude of the charge on an electron is e= 1.60 x 10 C and
23
Avogadro’s number N A= 6.02 x 10 /mole. What is the total amount of negative charge
6
in 4.50 moles of (neutral) chlorine atoms? (Answer: 7.37 x 10 C)
€
9. A certain ion has 8 protons, 7 electrons and 6 neutrons. What is the net charge of this ion?
€
Express your answer
in fundamental charge units (the charge of a proton is 1).
(Answer: 1)
€
10. (a) (Metals, non metals) are good conductors of electricity. (Answer: metals)
(b) Explain why the materials of part (a) are good conductors of electricity.
(Answer: Metals have many free electrons. These electrons are not tightly held to a
nucleus. The free electrons can move about and transfer charge from one part of the
metal to another.)
11. An electroscope is grounded by touching its knob. A positively charged rod is brought close
to the knob but does not touch the electroscope. The rod is then moved away from the
electroscope.
(a) When the rod is close to the knob of the electroscope, the knob is (neutral, positively
charged, negatively charged). (Answer: negatively charged)
(b) When the rod is close to the knob of the electroscope, the leaves are (neutral, positively
charged, negatively charged). (Answer: positively charged)
(c) The leaves are (collapsed, diverged) when the rod is near the electroscope.
(Answer: diverged)
(d) The net charge on the electroscope is (neutral, positive, negative) when the charged rod is
near the electroscope. (Answer: neutral)
(e) The leaves are (collapsed, diverged) when the rod is withdrawn. (Answer: collapsed)
(f) After the rod is withdrawn,, the electroscope’s knob is (neutral, positively charged,
negatively charged). (Answer: neutral)
(g) After the rod is withdrawn,, the electroscope’s leaves are (neutral, positively charged,
negatively charged). (Answer: neutral)
12. If any charged object is brought near the knob of an uncharged electroscope then
(the leaves will be neutral, the leaves will have the same type of charge as the object, the leaves
and the object will have opposite types of charge). (Answer: the leaves will have the same type
of charge as the object)
13. An uncharged electroscope’s knob is touched with a negatively charged rod and then the rod is
removed.
(a) What is the type of charge on the knob of the electroscope after the rod is removed?
(Answer: negative)
(b) What is the type of charge on the leaves of the electroscope after the rod is removed?
(Answer: negative)
(c) The electroscope was charged by a process called ________. (Answer: conduction)
(d) After the rod is removed, the leaves are (collapsed, diverged). (Answer: diverged)
(e) If a positively charged rod is brought close to the knob of the electroscope, the leaves
(collapse, diverge further, are not affected). (Answer: collapse)
14. Residual charge of an electroscope by induction.
Suppose you wish to place a net negative charge on an electroscope and have a (positively)
charged glass rod that has been rubbed with silk. The following steps (not listed in the correct
order) are involved.
Remove finger
Remove your finger from the electroscope’s knob while keeping the positively charged rod
near the knob.
Introduce rod
Move the positively charged rod near the electroscope’s knob. Do not touch the knob with the
rod.
Remove rod
Remove the positively charged rod from the vicinity of the electroscope.
Ground electroscope
Touch the electroscope’s knob with your finger while the positively charged rod is near the
electroscope’s knob.
List these steps (Remove finger, Introduce rod, Remove rod, Ground electroscope) in
chronological order in the table. Put the earliest step in the first row and the latest step in the
last row. Then complete the table by indicating the charge (positive, negative or neutral) on
each part of the electroscope immediately after that row’s step is completed.
Step
Earliest
step
Latest
step
Net charge on
Charge on knob Charge on leaves electroscope just
just after step is just after step is after step is
completed
completed
completed
Answer:
Step
Earliest
step
Latest
step
Net charge on
Charge on knob Charge on leaves electroscope just
just after step is just after step is after step is
completed
completed
completed
Introduce rod
Negative
Positive
Neutral
Ground electroscope
Negative
Neutral
Negative
Remove finger
Negative
Neutral
Negative
Remove rod
Negative
Negative
Negative
15. A positively charged rod is brought near an electroscope that was charged by induction using a
negatively charged rod. As the rod is brought close to the electroscope, its leaves will
(collapse, diverge further, not be affected). (Answer: diverge further)
16. A charged rod is used to charge an electroscope by conduction.
(a) The electroscope and rod end up with (the same type of charge, opposite types of charge)
(Answer: the same type of charge)
(b) The rod ends up with (less charge than, the same amount of charge as, more charge than) it
originally had. (Answer: less charge than)
17. A charged rod is used to charge an electroscope by induction.
(a) The electroscope and rod end up with (the same type of charge, opposite types of charge)
(Answer: opposite types of charge)
(b) The rod ends up with (less charge than, the same amount of charge as, more charge than) it
originally had. (Answer: the same amount of charge as)
18. True or False
(a) Charge is always conserved. (Answer: True)
(b) There are exactly two types of charge. (Answer: True)
(c) If you ground an insulator then all of its charge is neutralized. (Answer: False)
(d) The chemical properties an atom are due to the arrangement of its electrons. (Answer: True)
(e) Non metals are electrical insulators. (Answer: True)
(f) The mass of a proton is exactly the same as the mass of a neutron. (Answer: False)
(g) The magnitude of a proton’s charge is exactly equal to the magnitude of an electron’s
charge. (Answer: True)
(h) Electrons have no mass. (Answer: False)
(i) Almost all of the mass of an atom is found in its nucleus. (Answer: True)
(j) Almost all of the charge in an atom is found in its nucleus. (Answer: False)
(k) The gravitational force is much weaker than the electrical forces or nuclear forces inside an
atom. (Answer: True)
(l) The strong force between two protons is stronger than the electrical force between the
protons. (Answer: True)
(m) The strong force acts over a larger distance than the electrical force. (Answer: False)
(n) The diameter of an atom is about ten times the diameter of its nucleus. (Answer: False)
(o) In a neutral atom, the number of protons always equals the number of electrons.
(Answer: True)
(p) All stable atoms have the same number of neutrons as protons. (Answer: False)
(q) Two different isotopes of the same element must have the same atomic number.
(Answer: True)
(r) Two different isotopes of the same element must have different mass numbers.
(Answer: True)
(s) In the Bohr model of the atom, electrons have definite orbits around a small, dense
nucleus. (Answer: True)
(t) In the modern model of the atom, electrons do not have definite locations within the
atom nor definite orbits around the nucleus. (Answer: True)
(u) All entities in the universe have both wave-like and particle-like properties.
(Answer: True)
(v) An uncharged electroscope can be used to detect charge and determine the sign of the
detected charge. (Answer: False)
(w) You can use an electroscope with a known type of charge to determine the type of charge
on an object. (Answer: True)
(x) Water is a polar molecule. (Answer: True)
(y) Static electricity experiments work best in humid weather. (Answer: False)
(z) Charge is a scalar quantity. (Answer: True)
19. State the number of protons, neutrons and electrons in the neutral atom. 40
19K
(Answer: Number of protons= 19, Number of neutrons= 21, Number of electrons= 19)
20. A charge of −2.0 x 10 −4 C and a charge of 8.0 x 10−4 C are separated by .30 m.
(a) Do the charges attract or repel? (Answer: attract)
€
(b) How does the magnitude of the force exerted on the −2.0 x 10 −4 charge compare with the
magnitude of the force exerted on the 8.0 x 10−4 charge? (Answer: The forces are equal in
€magnitude)
€
(c) What is the magnitude of the force between the charges? (Answer: 1.6 x 10 4 N)
€
−5
€
21. Conducting sphere A has charge −6.4 x 10 C and sphere B is an identical conducting sphere
with a charge of 1.8 x 10−5 C. The spheres are allowed to touch and are then moved so that
€
their centers are .12 m apart.
(a) Do the spheres attract or repel? (Answer: repel)
€ of the force between the spheres? (Answer: 330 N)
(b) What is the magnitude
€
22. Sphere A has charge q A and sphere B has charge q B. The distance between the centers of the
spheres is d. The force between the spheres has magnitude F. The charge on sphere A is
changed to 2.8 q A and the charge on sphere B is quadrupled. The distance between the centers
of the spheres is changed to .90 d. What is the new force that acts between the spheres?
Answer in terms
of F. (Answer: 14 F) €
€
€
23.
N
q1
q1 = 1.7 x 10−5 C
W
E
q 2 = − 5.6 x 10−5 C
€
82 cm
€
S
q 3 = 9.8 x 10−6 C
€
q2
€
q3
69 cm
€
€
(a) How many more electrons are there than protons on sphere 2? (Answer: 3.5 x 1014 )
(b) What is the magnitude of the force that sphere 1 and sphere 3 exert on sphere 2?
(Answer: 16 N)
(c) What is the direction of the force that sphere 1 and sphere 3 exert on sphere 2?
(Answer: 51° N of E)
€
24. The charge on a proton is 1.60 x 10−19 C. The mass of an electron is 9.11 x 10−31 kg. A
hydrogen atom contains a proton and an electron separated by 5.0 x 10−11 m. If the electron
orbited the proton in a circular orbit then what would the orbital speed be? Consider the
electrical force between the proton and the electron. Ignore the gravitational force.
€
(Answer: 2.2 x €
10 6 m/s)
€
25. The charge on sphere A is −2.2 x 10 −6 C. The distance between the centers of the spheres
is .40 m. The mass of sphere B is 660 grams.
€
€
60°
A
B
€
(a) What is the tension in the rope attached to sphere B? (Answer: 13 N)
(b) What is the charge on sphere B? (Answer: 9.1 x 10−5 C)
€
26. State whether it would be possible or impossible to put a charge of the given magnitude on a
sphere.
(a) 3.00 x 10−21 C (Answer: impossible)
(b) 6.80 x 10−18 C (Answer: impossible)
(c) 5.12 x 10−18 C (Answer: possible)
€ 27. The electric field lines in a given region of space are shown.
€
(a) Draw a vector indicating the force on a positive test charge located at point X.
(b) Draw a vector indicating the force on a negative test charge located at point Y.
€
X
Y
Answer:
X
Y
28. True or False
(a) Electric field lines always start on a positive charge and end on a negative charge.
(Answer: True)
(b) The electric field is strongest where the field lines are closest together. (Answer: True)
(c) Electric field lines due to stationary charges are never closed loops. (Answer: True)
(d) Electric field lines may cross. (Answer: False)
(e) Field lines are perpendicular to the electric field vector at each point. (Answer: False)
(f) The electric field at a point does not depend on the size of the small test charge used to
measure the field. (Answer: True)
(g) The electric field intensity is the force per unit charge experienced by a test charge that is
located in the electric field. (Answer: True)
29. A 26 µC charge located at point P experiences a force of 8.9 N.
(a) What is the electric field intensity at point P? (Answer: 3.4 x 105 N / C)
(b) What force would a 35 µC charge experience at point P? (Answer: 12 N)
€ 30. An electron (mass= 9.11 x 10−31 kg) accelerates at the rate of 4.2 x 104 m /s2 in an electric
field. What is the electric field intensity? (Answer:€ 2.4 x 10−7 N/C)
€
31. What is the electric field intensity 2.7 m from a point charge of 6.0 x 10−4 C?
€
€
(Answer: 7.4x105 N/C)
€
32.
q1 = 4.8 x 10−4 C
€
3.9 m
€
1.3 m
q 2 = 5.4 x 10−4 C
q1
€
X
€
q2
€
(a) What is the electric field intensity at point X? (Answer:
1.8 x 10 6 N/C)
(b) How far to the right of q1 would the electric
€ field intensity be zero? (Answer: 1.9 m)
€ many joules of electrical energy are
33. The potential difference across a lamp is 12 V. How
changed into light€and heat if a charge of 5.0 C passes through the lamp? (Answer: 60 J)
34. Express the unit of electric potential in fundamental MKS units (kg, m, s and C).
kg •m 2
(Answer: volt=
)
€
C •s2
35. The potential difference between two points in an electric field is the amount of ___ done per
coulomb by the field when a charged particle moves from one point to the other. (Answer:
work)€
36. (a) The electric field intensity equals the potential ____. (Answer: gradient)
(b) Express the unit of electric field intensity in volts and meters. (Answer: volts/meter)
37. The electric field intensity between two parallel plates is 3.3 x 104 N/C. The plates are 2.5 cm
apart.
(a) What is the potential difference between the plates? (Answer: 830 V)
(b) How much work would be required to move a charge of 50 µC from the negative plate to
to the positive plate? (Answer: .041 J) €
38. A particle has mass 4.7 x 10−5 kg and charge 3.2 x 10−3 C. The particle accelerates from rest
€ a speed of 3.5 x 103 m/s. The particle
from a positive plate and strikes a negative plate with
travels between the plates in 1.5 x 10−2 s.
(a) What is the electric field intensity between the plates? (Answer: 3400 N/C)
€
€
(b) What is the potential difference between the plates? (Answer: 9.0 x 10 4 V)
€ between the plates? (Answer: 11 N)
(c) What force does the particle experience as it travels
€
€
39. A particle has mass 3.9 x 10−3 g and charge 610 µC. The particle travels between two charged
plates. The particle starts at rest and strikes the negative plate with a speed of 580 m/s. The
distance between the plates is 35 cm.
(a) What is the electric field intensity between the plates? (Answer: 3.1 x 103 N/C)
(b) What €
is the potential difference across
€ the plates? (Answer: 1100 V)
40. A particle has charge 1.7 x 10−4 C. The particle experiences a force of 8.9 x 10−2 N as it travels
€
between charged plates that are 27 cm apart.
(a) What is the electric field intensity between the plates? (Answer: 520 N/C)
(b) What is the potential difference across the plates? (Answer: 140 V)
€
€
41. The electric field intensity between two parallel plates is 6400 N/C. The plates are 25 cm apart.
A particle has mass 2.0 x 10−4 kg and charge 720 µC. The particle starts from rest and is
accelerated from the positive plate to the negative plate.
(a) What is the potential difference between the plates? (Answer: 1600 V)
(b) What is the potential gradient? (Answer: 6400 N/C)
(c) What €
is the acceleration of the particle?
€ (Answer: 2.3 x 104 m /s2 )
(d) How much work is done on the particle as it travels from one plate to the other?
(Answer: 1.2 J)
(e) With what speed does the particle strike the negative plate? (Answer: 110 m/s)
€
−3
42. A particle of mass 3.9 x 10 kg and charge 9.3 x 10−6 C floats in the electric field between two
charged plates. If the plates are 80 cm apart then what is the potential difference between the
plates? (Answer: 3300 V)
€
HOMEWORK
€
€
GUIDE
Section in the
Notes
Worksheet Problems
16.1 to 16.7
1 to 19
16.8
20 to 26
16.9
27 to 32
16.10
33 to 42