UNIVERSITY OF BOTSWANA
Department of Physics
PHY 122 - Electricity & Magnetism, and Elements of Modern Physics
2019/2020
ASSIGMENT – EM 3
Tutorial Dates 27/28 February, 2020
1.
Find the total electric potential at a point in hydrogen atom between a proton and
electron which are 0.05nm and 0.09nm from the point respectively.
2.
Two parallel plates positioned horizontally are separated by 16 cm. The bottom plate
has an electric potential of +600V while the upper plate is held at -200V.
(a) What is the magnitude and direction of the electric field in between the plates?
(b) What are the potentials at distances 4 cm, 8 cm, and 12 cm from the lower plate?
3.
⁄ passes
A proton travelling in a uniform electric field of magnitude
⁄ towards point B, in the same direction as the
point A with velocity
electric field. The proton undergoes a displacement of
from point A and to point
B.
(a) Find the change in the electric potential between point A and B.
(b) Find the change in potential energy of the proton-field system for this
displacement.
(c) Calculate its speed at point B.
4. Two small spherical object that carry charges of +3 µC and -5 µC are initially separated
by 5 cm.
(a) What is the change in electrostatic potential energy if the separation is increased
by 2 cm?
(b) How much work has been done?
(c) What is the change in electrostatic potential energy if the separation is reduced to
2 cm?
(d) Is the work done on the charges in the latter case?
5.
Four charges are arranged in a square of sides 0.52m, starting from top left going in a
clockwise direction:
,
,
and
. Point B
is at the centre and point A is midway between
and . With the aid of a diagram:
(a) Calculate the energy required to assemble the charges into the shown
configuration.
(b) Calculate the electric potential at points A and B.
(c) Find the energy required to bring a charge q0 = -10μC
(i)
from infinity to point B
(ii)
from point A to B.
(d) If q0 (of mass 5g) is released from rest at point B and accelerates towards A,
calculate its speed by the time it reaches point A.
ZGK/VRKM/ MT/OEM 2019/2020