E fields and B fields

1) Draw
the electric field lines surrounding a stationary, negative, point charge.

2) Draw
the electric field lines surrounding two stationary point charges next to each
other, one positive and the other negative.

3) Draw
the electric field lines surrounding two stationary point charges, still next
to each other, but this time both charges are positive.

4) The
picture below shows a positive charge moving past a second, stationary charge.
What is the direction of the *magnetic*
force on the moving charge? What is the direction of the *electric* force?

5) The
picture below shows an electron moving between two parallel metal plates. The
bottom plate is positive, and the top plate is negative. First, draw the
electric field lines between the plates. Second, what is the direction of the electric
force on the moving electron? Third, is there a magnetic force?

6) A + 25
mC charge is 0.75 m to the
right of a + 37 mC charge. What is the field (magnitude and direction) experienced by
the + 25 mC charge?

7) A
negative test charge is 0.45 m to the right of a + 9.5 mC charge. What is the field (magnitude and direction)
experienced by the test charge?

8) Fire
an electron through a magnetic field. The velocity makes an angle with the
field lines. Which angles (note the plural) will give the maximum magnetic force?
Which angles give the minimum?

9) A
charged particle moves at 7.5 ´ 10^{4} m/s through a magnetic field of 5.9 ´ 10^{-5} T, and experiences a 1.5 ´ 10^{-4} N force. The angle between the
particle’s velocity and the field lines is 35°. What is the magnitude of the
charge?

10) A
proton moves into a 0.25 T magnetic field. The proton moves perpendicular to
the field which causes it to move in a circle of radius 0.25 m. First, find the
speed of the proton. Second, find the centripetal force exerted on the proton.
The charge on a proton is 1.60 ´ 10^{-19} C, and the mass of a proton is 1.67 ´ 10^{-27} kg.

11) It is *impossible* for a constant magnetic field
to do work on a moving charge, even though the field exerts a force on the
charge. Please explain. (Use the right hand rule!)

12) You’ve
been given the equation for the magnetic force on a moving charge (i.e. F = qvBsinq). However, sometimes you have to deal not with individual point
charges, but with large numbers of point charges. In these cases, it’s much
easier to think in terms of currents rather than point charges. Current is
defined as I = q/t where I is the current. Using these equations, and your old
friend v = d/t, derive the eqution for the force on a
length of wire, starting from the equation for the force on a point charge.