electric field

Question 1

the electric field at point P

Answer 1

E = F / q0

q0 is the test charge

Question 2

the SI unit for the electric field

Answer 2

the newton per coulomb ( N/C )

Question 3

electric field line

Answer 3

1) extend away from positive charge and toward negative charge
2) the direction of a straight field line or the direction of the tangent to a curved field line gives the direction of field at that point
3) the number of lines per unit area, measured in a plane that is perpendicular to the lines, is proportional to the magnitude of E

Question 4

electric field at point P due to a point charge q1

Answer 4

put a test charge q0 at point P

E = F / (q0) = ( k q1 ) / r^2 ; along the direction of r

Question 5

the electric field at point P due to more than one point charge

Answer 5

can be found by superposition
put a test charge q0 at that point
E = ( F0 / q0 )
   = ( F01 / q0 ) + ( F02 / q0 ) + ...... + ( F0n / q0 )
   = E1 + E2 + ...... +En

Question 6

the electric field at point P due to an electric dipole

Answer 6

E = p / ( 2 π ε0 z^3 )
z = distance from dipole center to the point P

Question 7

electric dipole moment

Answer 7

electric dipole moment = p = q·d

the direction of d is from -q to +q

Question 8

measures of electric charge

Answer 8

1) charge —— q —— ( C )
2) linear charge density —— λ —— ( C / m^1 )
3) surface charge density —— σ —— ( C / m^2 )
4) volume charge density —— ρ —— ( C / m^3 )

Question 9

electric field due to a circle line charge

Answer 9

dq = λ ds
E = ( z λ ) ( 2πR ) / ( 4π εо ) ( z^2 + R^2 )^(3/2)

r = the distance from P to ds
R = the horizontal distance from P to ds = the radius of the circle
z = the vertical distance from P to ds

Question 10

electric field due to a charged disk

Answer 10

λ = σ dr
E = ( z σ dr ) ( 2πr ) / ( 4π εо ) ( z^2 + r^2 )^(3/2)
=

R = the radius of the disk
z = the vertical distance from P to ds