Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

Hi, I have to make 100 test of electromagnetism, but I have problems to these 6, I don´t know solutions.
Can anyone help me?
thanks

1 - What is the directional derivative in the direction v3,4,0)
of the scalar field f(x,y,z)=x2+ y2 +z2 at the point (1,0.5,1)?
    a. 3
    b. 0
    c. 1/3
    d. 1/2
    e. 2


2 - A uniform line charge of linear charge density l= 10.0 nC/m extends
from x= 5 m to x= 8 m. The magnitude of the electric field at x = 10 m is
    a. 27.0 N/C
    b. 37.5 N/C
    c. 15.3 N/C
    d. 9.62 N/C
    e. 18.8 N/C


3 - The electric potential in a region of space is given by
V(x, y, z) = 10x + 20y + 30z V The z-component of the electric field
in this region is
    a. 20 V/m
    b. 30 V/m
    c. –30 V/m
    d. –20 V/m
    e. –10 V/m


4 - A positively charged particle is moving northward in a magnetic field. 
The magnetic force on the particle is toward the northeast. 
What is the direction of the magnetic field?
      a. south   
      b. down   
      c. This situation cannot exist   
      d. west   
      e. up


5 - Two long, straight parallel wires 7.6 cm apart carry currents of equal magnitude I.
They attract each other with a force per unit length of 4.3 nN/m. 
The current I is approximately
    a. 37 mA   
      b. 59 mA   
      c. 40 mA   
      d. 1.6 mA   
      e. 4.0 mA


6 - An 8.0 mH inductor and a 2.0 Ω resistor are wired in series to an ideal battery.
A switch in the circuit is closed at time 0, at which time the current is zero.
The current reaches half its final value at time:
      a. 250 s   
      b. 170 s   
      c. 4.0 ms   
      d. 3 s   
      e. 2.8 ms