Assignment (Spring 2020)
Department of Mathematics and Physics
Course Name: Physics II
Course code: Phy108
Section: 18
Last date of submission: 04.06.2020
Important notes:
- Please write student ID and page number at the top of each page of your assignment.
-You have to answer all the questions.
-You may prepare it by typing or by hand writing, for submission please use pdf only.
-If hand written please write your answers neatly in clear white paper and scan the answers using your
phone.
-You should ‘handed in’ the completed assignment only through Google classroom (no email attachment).
-You have to solve the assignment with honesty and integrity.
-Submit as early as possible.
-You should not share your solutions with others.
-It may go through 'plagiarism test' on your assignment, significant similarity (copying from others)
would severely reduce marks from both.
-This submission will carry maximum 30% marks for grading.
Question 1:
(a) When a dielectric is inserted into an isolated and charged capacitor, the stored energy decreases
to 33% of its original value. (i) What is the dielectric constant? (ii) How does the capacitance
change?
(b) Define the term equivalent resistance. The South American eel Electrophorus electricus
generates 0.80-A pulses of current at a voltage of about 640 V. At what rate does it develop power
when giving a shock to its prey? If the shock pulse lasts 1 ms, how much energy is delivered?
(c) List some applications of RC circuits. For the RC circuit shown in Figure, the capacitor with
initial charge q0 is discharged through the resistor. What multiple of the time constant τ gives the
time the capacitor takes to lose (a) the first one-third of its charge and (b) two-thirds of its charge?
Question 2:
(a) Briefly discuss about the Ohm’s law and microscopic views of conduction through a metal.
(b) (i) Discuss the similarities and differences between the electrical force on a charge and the
magnetic force on a charge.
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⃗ where I =2.7A and 𝐿
⃗ =
(ii) A straight segment of a current-carrying wire has a current element 𝐼𝐿
3.0 𝑐𝑚 𝑖̂ + 4.0 𝑐𝑚 𝑗̂. The segment is in a region with a uniform magnetic field given by1.3 𝑇 𝑖̂.
Find the force on the segment of wire.
(c) (i) Define the magnetic dipole moment of a current loop.
(ii) A circular current loop of radius 2.0 cm carries a current of 2.0 mA. (a) What is the magnitude
of its magnetic dipole moment? (b) If the dipole is oriented at 30 degrees to a uniform magnetic
field of magnitude 0.50 T, what is the magnitude of the torque it experiences and what is its
potential energy?
Question 3:
(a) Discuss the differences and similarities between Gauss’s law for magnetism and Gauss’s law
for electricity.
(b) Parallel wires 1 and 2 carry currents I1 and I2 respectively, where I2 = 2I1. The two currents are
in the same direction. The magnitudes of the magnetic force by current 1 on wire 2 and by current
2 on wire 1 are F12 and F21 respectively. Find the relation between the forces.
(c) Make a field-line sketch of the magnetic field due to the currents in the pair of identical coaxial
coils shown in Figure. Consider two cases: (a) the currents in the coils have the same magnitude
and have the same direction and (b) the currents in the coils have the same magnitude and have
the opposite directions.
Question 4:
(a) Is the magnetic field of a current loop uniform? Consider a uniformly wound solenoid having
N turns and length L. Assume L is much longer than the radius of the windings and the core of the
solenoid is air. (i) Find the inductance of the solenoid. (ii) Calculate the inductance of the solenoid
if it contains 300 turns, its length is 25.0 cm, and its cross-sectional area is 4.00 cm2. (iii) Calculate
the self-induced emf in the solenoid if the current it carries decreases at the rate of 50.0 A/s.
(b) Compare the role of a capacitor and an inductor in the electrical circuits. Discuss briefly about
the statement, ‘Capacitors, Resistors, and Inductors Store Energy Differently’.
(c) Describe what effect the resistance of the connecting wires has on an oscillating LC circuit.
Question 5:
(a) Two solenoids are equal in length and radius, and the cores of both are identical cylinders of
iron. However, solenoid A has three times the number of turns per unit length as solenoid B. (i)
Page 2 of 3 (Phy 108 Assignment)
which solenoid has the larger self-inductance? (ii) What is the ratio of the self-inductance of
solenoid A to the self-inductance of solenoid B?
(b) A student asserted that if a permanent magnet is dropped down a vertical copper pipe, it
eventually reaches a terminal velocity even if there is no air resistance. Why should this be? Or
should it? Explain your answer.
(c) What are the relative advantages and disadvantages of Ampere’s law and the law of Biot and
Savart for practical calculations of magnetic fields?
Question 6:
(a) What are the Maxwell’s equations? Discuss briefly with their significances.
(b) An electron moves at 0.100c (c is the speed of light) as shown in Figure. Find the magnitude
and direction of the magnetic field this electron produces at the following points, each 2.00 µm
from the electron: (a) points A and B; (b) point C; (c) point D.
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