Electricity and Magnetism Answers

Two concentric conducting loops have radii Ra and Rb (Ra>>Rb). The inner loop has
current I flowing counter-clockwise through it, and the outer loop has no current. The outer
loop has resistance R. The inner loop is cut by scissors, so that in a fairly small duration
current in it drops to zero. What is the direction of induced current in the outer loop? How
much total charge passes a point in the loop during the period this current flows?

1. An electrically neutral glass rod is rubbed against a neutral piece of silk. During this process 2.0 x 1015 electrons are transferred from the rod to the silk.
a. How much charge (in coulombs) did the silk acquire?

b. What charge does the glass rod have after being rubbed on the silk?

A uniform electric field is produced between two parallel plates that have a PD of 100V across
them and separated by a distance of 20mm.

CONSTANTS
Acceleration due to gravity = 9.82 = m 2
s
Eo m
= s − 889 12 .
Speed of light = 3 108 x m
s Mass of an Electron = 911 10 31 . x kg −
Mass of proton = 1 67 10 27 . x kg − Charge on an Electron = 1 6 10 19 . x C −
Charge on proton = Planck’s Constant =
1eV = 1.6x10-9J

ii) Calculate
a) The force electron on an electron in the field. (6 marks)
b) The work done in moving an electron from one plate to another in
the field.

A charge particle X (-60μC) is on the x axis at the point (2,0) and a particle Y( - 100μC) is on
the x axis at the point (5,0). Calculate
i) The electric field strength and electric potential at the point (4,0). (10 marks)
ii) The coordinates of the point on the x axis where the electric field strength will be zero.

Suppose that two point chargers each with a charge of 1 coulomb are separated by A distance of 6.44 m determine the magnitude of the electrical force between them

.A particle of charge 2 X 10^-19 C is placed in the upward electric field of 10 N/C. What is the direction of gravitational force on the charge particle?

Can anyone verify my answer ?
3. A negatively charged particle is moving directly away from you when it enters a magnetic field pointing downward. Which direction is the force on the negatively charged particle from the magnetic field?
A. no direction, the force is 0
B. away from you
C. toward you
D. up
E. down
F. left
G. right
==> to the right

4.A positively charged particle is directly in front of you and moving to your left when it enters a magnetic field pointing to your right. Which direction is the force on the positively charged particle from the magnetic field?
A. no direction, the force is 0
B. away from you
C. toward you
D. up
E. down
F. left
G. right
==> A. Force is 0

Can anyone verify my answer ?
1. A conductor carrying a current is arranged so that current flows east. What direction is the magnetic field from the wire directly above the wire (away from the ground)?
A. no direction, there is no field
B.south
C. west
D. up
E. down
F. east
G. clockwise
H. counterclockwise
==> Clockwise

2. A positively charged particle is directly in front of you and moving to your right when it enters a magnetic field pointing upward. Which direction is the force on the positively charged particle from the magnetic field?
A. no direction, the force is 0
B. away from you
C. toward you
D. up
E. down
F. left
G. right
==> toward you

Obtain the directional derivative for a scalar field ϕ(x, y, z)=(3x^2y-y^3z^2) at the point (1, -2, -1) in the direction Î+ ĵ +k̂

A particle with charge 6.80 micro coloumbsis moving with velocity