Ch 5 - Electrostatic and Magnetism

Question 1

What is the SI unit of charge?

Answer 1

coloumb

Question 2

What is the charge for protons and electrons?

Answer 2

= 1.6 x 10^-19 C

- they have the same charge but different masses

Question 3

What are conductors?

Answer 3

allow the free and uniform passage of electrons when charged.
- ex. blood, copper, iron, sulfuric acid

Question 4

What are insulators?

Answer 4

resist the movement of charge and will have localized areas of charge that do not distribute over the surface of the material
- ex. hair, glass, distilled water

Question 5

What is Coulomb’s law?

Answer 5

• gives the magnitude of the electrostatic force vector between 2 charges
• the force vector always points along the line connecting the centers of the 2 charges
  Fe = (kq1q2)/r^2

Question 6

What is an electric field?

Answer 6

• the ratio of the force that is exerted on a test charge to the magnitude of that charge
  E = Fe/q = kQ/r^2
• electric fields are produced by source charges (Q); when a test charge (q) is placed in an electric field (E), it will experience an electrostatic force (Fe) equal to qE

Question 7

What are field lines?

Answer 7

• can represent electric field vectors for a charge
• point away from negative charge and towards positive charge
• the denser the field lines, the stronger the electric field
• field lines of a single charge never cross each other

Question 8

What direction do positive and negative test charges move?

Answer 8

• positive: in the direction of the field lines

- negative: in the direction opposite of the field lines

Question 9

What is electric potential energy?

Answer 9

the amount of work required to bring the test charge from infinitely far away to a given position in the vicinity of a source charge
U = kQq/r

Question 10

How is the electric potential energy of a system affected when charges 2 like charges and opposite charges react?

Answer 10

• energy increases when like charges move toward each other or when 2 opposite charges move further apart
• energy will decrease when 2 opposite charge move toward each other or when 2 like charges move further apart

Question 11

What is electric potential?

Answer 11

the electric potential energy per unit charge
- different points in the space of an electric field surrounding a source charge will have difference electric potential values
- units are volts
V = U/q = kQ/r

Question 12

What is the potential difference (voltage)?

Answer 12

the change in electric potential that accompanies the movement of a test charge from one position to another
- units are volts

Question 13

What does potential difference depend on?

Answer 13

it is path independent and depends only on the initial and final positions of the test charge

Question 14

Which direction to test charges move towards whether positive or negative?

Answer 14

move spontaneously in whichever direction results in a decrease in their electric potential energy

• positive will move spontaneously from high potential to low potential
• negative will move spontaneously from low to high potential

Question 15

What equipotential lines?

Answer 15

• the set of points within space at which the potential difference between any 2 points is 0
• always perpendicular to electric field lines

Question 16

How does work done relate to equipotential lines?

Answer 16

• work will be done when a charge is moved fone equipotential line to another; the work is independent of the pathway taken between the lines
• no work is done when a charge moves from a point on an equipotential line to another position on the same line

Question 17

What is an electric dipole?

Answer 17

• generated from 2 charges of opposite sign that are separated by a fixed distance
  p = qd

Question 18

What do electric dipoles experience in an external electric field?

Answer 18

• a net torque until it is aligned with the electric field vector
• an electric field will not induce any translational motion in the dipole regardless of its orientation with respect to the electric field vector

Question 19

What is the difference between a diamagnetic, paramagnetic, and ferromagnetic materials?

Answer 19

• di: posses no unpaired electrons and are slightly repelled by a magnet
• para: posses some unpaired electrons and become weakly magnetic in an external magnetic field
• ferro: posses some unpaired electrons and become strongly magnetic in an external magnetic field

Question 20

What type of magnetic fields do current carrying wires create?

Answer 20

magnetic fields that are concentric circles surrounding the wires

Question 21

What type of charges do external magnetic fields exert forces on?

Answer 21

charge moving in any direction except parallel or antiparallel to the field

Question 22

What is the Lorentz force?

Answer 22

the sum of the electrostatic and magnetic forces acting on a body

Question 23

What determines the direction of the magnetic force on a moving charge or current carrying wire?

Answer 23

the right hand rule

Question 24

When placed one meter apart from each other, which will experience a greater acceleration: 1 C of electrons or 1 C of protons?

Answer 24

though they are both subject to the same force, electrons will have greater acceleration because of its smaller mass

Question 25

What is the net charge of an object with 1 C of electrons and 3 moles of neutrons?

Answer 25

-1; neutrons do not affect charge

Question 26

What is the electric field midway between 2 negative charges in isolation?

Answer 26

0 because the 2 charges are the same so the fields exerted by each would cancel out

Question 27

What direction does the negative and positive electrostatic force point?

Answer 27

• neg: from one charge to the other (attractive)

- pos: from one charge away from the other (repulsion)

Question 28

How does a decrease in electric potential energy reflect on the stability of the system?

Answer 28

decrease indicates more stable

Question 29

What is the difference between electric potential energy and voltage?

Answer 29

• electric PE: ratio of charge’s electric PE to magnitude of the the charge itself
• voltage (potential difference): measure of change in electric potential which indicates the tendency of movement one way or the other

Question 30

How will a charge that is placed at a point of zero electric potential move relative to a source charge?

Answer 30

• a charge will move in such a way to minimize its PE
• placing a charge at a point of zero electric potential does not indicate that there is zero potential difference, so the charge may or may not move - and if it moves, it may move toward or away from the source charge depending on the sign of the source charge and test charge

Question 31

What is the voltage between 2 points on the equipotential line? Will this voltage cause a charge to move along the line?

Answer 31

• there is no voltage between 2 points on the equipotential line, so there will be no acceleration along the line
• however, there is a potential difference between different sets of equipotential lines, which can cause particles to move and accelerate

Question 32

Why is the electrical potential at points along the perpendicular bisector of a dipole zero?

Answer 32

• the perpendicular bisector of an electric dipole is an equipotential plane that is perpendicular to the axis of the dipole
• as such, the equation V = (kqd/r^2)cos is necessarily equal to 0 because cos90 = 0

Question 33

What is the behavior of an electric dipole when exposed to an external electric field?

Answer 33

a dipole will rotate within an external electric field such that its dipole moment aligns with the field

Question 34

What is a magnetic field?

Answer 34

• created by any moving charge - tesla (T)

- B = uI/2pi.r

Question 35

What is a magnetic force?

Answer 35

may be exerted on a charge that is moving in a magnetic field
Fb = qvBsin = ILBsin
sin0 = sin180 = 0

Question 36

What parts of the right hand rule are used for the magnetic force?

Answer 36

• thumb: velocity (indicates direction of movement - tangent to circle)
• fingers: field lines (fingers are parallel like the uniform magnetic field lines)
• palm: force on a positive charge
• back of hand: force on a negative charge

Question 37

How is an electric field’s direction at a given point defined?

Answer 37

defined as the direction of the force that would be exerted on a positive test charge in that position (meaning electrons would feel a force in the opposite direction)

Question 38

How are the change in potential energy and the change in potential related?

Answer 38

W = delta U = q delta V