Ch 5 - Electrostatics and Magnetism

Question 1

Charge of electron/proton

Answer 1

• e = 1.6E-19 C
• e is + or - for electron or proton

Question 2

Insulator and Conductor

Answer 2

• insulator - electrons more closely help to nucleus
  
  • less likely to spread charge
• conductor - electrons in loose cloud around nucleus
  
  • spread charge easily
  • distributes charge over surface

Question 3

Coulombs Law

Answer 3

• F = kq₁q₂ / r²
• electrostatic force between 2 charges
• k = 8.99E9 Nm²/C²

Question 4

w2Field lines

Answer 4

• represent electric field vectors
• away from positive charge
• toward negative charge
• dense lines, stronger field

Question 5

Types of Potential Energy

Answer 5

• Electric
• alastic
• gravitational
• chemical

Question 6

Electrical potential energy

Answer 6

• dependent on relative position of one charge with respect to another charge
• U = kQq/r
• U: potential energy
• decreasing U is increasing stability
• U increases as like charges move closer together
• U increases when dislike charges move farther apart

Question 7

Electric Potential

Answer 7

• ratio of the magnitude of a charge’s electrical potential energy to the magnitude of the charge itself
• V = U/q
• V = W_ab/q
  
  • ratio of work done to move a test charge form infinity to a point in an electric field surrounding a source charge divided by the magnitude of the charged
• 1 Volt = 1 J/C
• V = kQ/r
  
  • do not need test charge to find potential at a point in space
• Potential difference is voltage
• test charges spontaneously move to decrease electric potential
  
  • positive charge - move to decrease voltage
  • negative charge - move to increase voltage

Question 8

Equipotential lines

Answer 8

• potential at every point on the line is the same
• potential difference between points on the line is zero
• “lines” are actually spheres about a charge
• does require energy to move from one line to another

Question 9

electric dipole

Answer 9

• due to two equal and opposite charges being seperated by a small distance
• p = qd
  
  • p: dipole moment
• torque causes dipole to reorient itself with the electric field

Question 10

magnetic field

Answer 10

• caused by the movement of a charge
• electron moving through space
• current through a conductive material
• permanent magnets

Question 11

dimagnetic, paramagnetic, ferromagnetic

Answer 11

• diamagnetic - atoms without unpaired electrons, no net magnetic field
  
  • common materials - wood, glass, plastic, skin
• paramagnetic - atoms with unpaired electrons
  
  • become weakly magnetized when in presence of magnetic field that aligns the dipoles
  • Al, Cu, Au
• Ferromagnetic - unpaired electrons and permanent atomic magnetic dipoles
  
  • typically randomly oriented
  • highly magnetized when in presence of magnetic field
  • Fe, Ni, Co
  • field lines out of N and into S pole of bar magnet

Question 12

Magnetic fields

Answer 12

• Straight infinite wire with current
  
  • B = u₀I / 2pi*r
  • use right hand rule to determine direction of field lines
  • straight wire makes concentric rings around the wire
• Circular loop with current
  
  • B = u₀I / 2r
  • for field at center of loop
• u₀ = 4πE-7 Tm/A
• Tesla: 1 T = 1 N*s / m*C

Question 13

Lorentz force

Answer 13

• sum of electrostatic and magnetic force

Question 14

Magnetic Force

Answer 14

• F = qvBsin(theta)
• moving parallel to the magnetic field results in no magnetic force
  
  • sin (0) = 0
  • sin (180) = 0

Question 15

Right hand rule for magnetic force

Answer 15

• thumb - velocity
• fingers - field lines
• palm - positive particle
• back of hard - negative particle

Question 16

Force on current carrying wire

Answer 16

• F = ILBsin (theta)
• I - current
• L - length
• B - magnetic field
• current is flow of positive charge
  
  • use this info for right hand rule