Q1

The field is not always parallel to the surface of the Earth.  The compass will tend to line up with the local direction of the magnetic field. This can cause the dip in the compass.

Q2

Point thumb in direction of current (the the left) and the fingers will curl in the direction of the field lines. They get weaker further away from the line.

a

F = ILBsinq     ð F/L = IBsinq = 7.6 N/m

b

P 1

a.

We can use equation 20-1 to find the foce at the given angle and length

F = ILBsinq       ð    F/L = 7.6N/m

b.

F/L = F = ILBsinq       ð    F/L = 5.3N/m

P10

We use equation 20-4 since the velocity and field are perpendicular

Fmax = qvB = 1.05x10^-13 N

Using the right hand rule the force is directed North

P27

With the assumption that the wire is long and straight, we can use equation 20-6

B_wire = m₀I/2pr   ð I = 2prB_wire/ m₀  = 69 A

P49

This is an application of equation 20-8 for the field inside a solenoid.

B = m₀IN/L   ð I = BL/m₀N = 94.3 A