Download Electricity: Forces and Charges and Fields – OH MY

Electricity: Forces and Charges and Fields – OH MY!
Name_________________________________________________Block__________
F= kC /q1/ /q2/
E = Kc _q__
kC = 8.99 x 109 F=ma
2
2
d
r
Note: μ= “micro” which is x 10-6 . For example 3.00 μC= 3.00 x 10-6 C
Remember- many calculations will need a test charge, which are assumed to
be positive (+) unless otherwise indicated.
1. An electric field of 12.0 N/C is directed along the positive x axis. What is the electric
force on an object with a charge of -6.00 C in this field?
2. An electric field of 1500 N/C is directed along the positive y-axis. What is the electric
force on an object with a charge of 5.0 x10-9 C in this field?
3. Millikan’s famous oil drop experiment measured the charge of an electron (by
suspending oil droplets in an electric field). If an oil droplet with a mass of
3.35 x 10-15 kg has the same charge as an electron. What electric force is required to
balance the weight of the oil droplet? (this looks complicated but needs one simple
older formula if you think about it)
E= F/q
#4 is for honors only: all others are for all students
Two equal charges of 3.00 μC (assume charges are + unless otherwise indicated) lie
along the x-axis: one is at the origin, the other is .55 m from the origin (to the right).
Find the magnitude and direction of the electric field at a point on the y-axis .25 m from
the origin. (this one will take awhile- it’s important that you do this one carefully to
make things faster later!)
5. A charge , q1=15.0 μC, is at the origin, and a second charge, q2= 5.00 x 10-8 C is on
the positive y-axis .500 m from the origin. Find the magnitude and direction of the
electric field at a point on the y-axis 1.000 m from the origin. (much like #4 but in a
straight line)
6. An electric field of 1663 N/C is directed along the positive x-axis. If the electric force
on a charge is 8.42 x 10-9 N, what is the charge?
7. An electric field of 4.0 x 103 N/C is directed downward. If the electric force on a charge
is 6.43 x 10-9 N, what is the charge?
8. The charge on both a proton and electron is the same magnitude: 1.60 x 10 -19 C (but
the charge is opposite, of course). A. If one of each of these particles is placed
5.3 x 10-11 m apart, how much electrical force is acting between the objects? B. In what
direction is this force?
9. A balloon gains a charge of – 8.0μC when it is rubbed again a pair of blue jeans (hintthe jeans are becoming equally charged). If the balloon is now held at a distance of 5.0
cm from the jeans…
a. how much force will the pants be experiencing due to the charges?
b. How much force will exist between the balloon and the pants? (Include direction)
c. What do you notice about the answer the a. vs. b.? Why is this?
10. Two electric point charges of +60.0 μC and +50.0 μC exert a repulsive charge on each
other of 175 N. How far apart must these charges be?
4.
1) 72.0 N 2) 7.5 x 10-6 N 3) 3.28 x 10-14 4) 1= 4.3x105 E2=7.5x104 Final answer is 4.7x105 N/C @ 990 5) 1= 1.35 x 105 N/C
2= 1.80 x103 N/C Final answer (after adding- both repel upward)1.37 x 105 N/C upward 6) 5.06 x 10-12 N/C 7) 1.6 x 10-12 C
8) 8.2 x 10-8 N 9) a. (use E=F/q then E= Kc q/r2
/
230N b. Use F= Kc /q1/q2 d2 230N 10) .393m