AIR UNIVERSITY Final Exam Fall 2012
Subject: Applied Physics PH-102
Class: BEMTS-I
Instructors: Dr Muhammad Anwar
Maximum Marks: 45
Max. Time: 3Hrs
Date: 08-01-2013
Note: Attempt all the nine questions. Each question carries equal marks.
x  t   5  3t  3t 2  t 3 gives in meters the displacement xt  of an object as a function of time t
1.
(1.5)
measured in seconds.
(a)
What are its initial position, velocity v and acceleration a ?
(b)
Is it an example of motion with constant acceleration a ?
(0.5)
(c)
(d)
When is its velocity v  0 ? Find the value of a at this time. `
Sketch x as a function of t .
(1.5)
(1.5)
2. (a)
(b)
3. (a)
(b)
(c)
4. (a)
(b)
A spring and block are in the arrangement of as shown in figure. When
(3)
the block is pulled out to X = +4 cm, we must apply a force of magnitude
360 N to hold it there. We pull the block to X = 11 cm and then release it.
How much work does the spring do on the block as the block moves from
Xi = +5 cm to Xf = +3 cm?
How much work is done by a force F = (2x N)i + (3 N)j, with x in meters, that moves a particle (2)
from a position ri = (2 m)i + (3 m)j to a position rf = - (4 m)i + (3 m)j?
The nucleus in an iron atom has a radius of about 4.0 x 10-15 m and contains 26 protons. What is (2)
the magnitude of the repulsive electrostatic force between two of the protons that are separated
by 4.0 x 10-15 m?
In the figure, particle 1 of charge +1 µC and particle 2 of charge -3.0 µC are
(2)
held at separation L= 10 cm on an x axis. If particle 3 of unknown charge q3 is
to be located such that the net electrostatic force on it from particles 1 and 2 is
zero, what must be the x and y coordinates of particle 3?
How many electrons would have to be removed from a coin to leave it with a charge of +0.1 C? (1)
The figure shows three non conducting rods, one circular and
two straight. Each has a uniform charge of magnitude Q along
its top half and another along its bottom half. For each rod, what
is the direction of the net electric field at point P?
Figure shows a non-conducting rod with a uniformly distributed
charge +Q. The rod forms a half-circle with radius R and
produces an electric field of magnitude Earc at its center of
curvature P. Find Earc.
(1)
(3)
(c)
An electron is released from rest in a uniform electric field of magnitude 2.00 x 10 4 N/C. (1)
Calculate the acceleration of the electron. (Ignore gravitation).
5. (a)
There is a certain net flux φi, through a Gaussian sphere of radius r enclosing an isolated charged (1)
particle. Suppose the enclosing Gaussian surface is changed to a Gaussian cube with edge length
equal to r. Is the net flux through the new Gaussian surface greater than, less than, or equal to φi?
(b)
6. (a)
(b)
7. (a)
(b)
(c)
8. (a)
(b)
9. (a)
(b)
In a figure below, two large thin metal plates are parallel and close to each other.
On their inner faces, the plates have excess surface charge densities of opposite
signs and magnitude 7.00 x 10-22C/m2. In unit-vector notation, what is the
electric field at points (i) to the left of the plates, (ii) to the right of them, and
(iii) between them?
The fig. shows a small non conducting ball of mass m = 1 mg and charge q = 20 nC
(3)
(distributed uniformly through its volume) hangs from an insulating thread that
makes an angle θ=30o with a vertical, uniformly charged non conducting sheet
(shown in cross section). Considering the gravitational force on the ball and
assuming the sheet extends far vertically and into and out of the page, calculate the
surface charge density σ of the sheet.
An unknown charge sits on a conducting solid sphere of radius 10 cm. If the electric field at 15 (2)
cm from the center of the sphere, has the magnitude 3 x 103 N/C and is directed radially inward,
what is the net charge on the sphere?
The figure here shows three arrangements according
(1)
to the protons. Rank the arrangements according to
the net electric potential produced at point P by the
protons, greatest first.
An infinite non conducting sheet has a surface charge density σ = 0.1 µC/m2 on one side. How (2)
far apart are equipotential surfaces whose potentials differ by 50 V?
A spherical drop of water carrying a charge of 30 pC has a potential of 500 V at its surface (with (2)
V=0 at infinity). What is the radius of the drop?
A straight, horizontal length of copper wire has a current i = 28A through it. What are the (3)
magnitude and direction of the minimum magnetic field B needed to suspend the wire that is to
balance the gravitational force on it? The linear density (mass per unit length) of the wire is 46.6
g/m.
What uniform magnetic field, applied perpendicular to a beam of electrons moving at 1.3 x 106 (2)
m/s, is required to make the electrons travel in a circular arc of radius 0.35 m?
The wire in the given figure carries a current i and consists of a circular arc of
radius R and central angle π/2 rad, and two straight sections whose extensions
intersect the center C of the arc. What magnetic field B does the current
produce at C?
(3)
A long cylindrical conductor of radius a = 2 cm carries a uniform current of 170 A. What is the (2)
magnitude of the current's magnetic field at radial distance 1 cm from the centre of conductor?
Some useful information: Acceleration due Earth’s gravity near its surface g
charge e  1.602  10
constant G
(4)
19
 9.8m / s 2 , Elementary
C , Mass of electron me  9.109  10 31 kg , mass of proton m p  1.673  10 27 kg , Gravitational
 6.673  10 11 N  m 2 / kg 2 , Permittivity constant  0  8.854  10 12 F / m , permeability
constant  0  1.257  10
6
H / m , horizontal component of the Earth’s magnetic field at the equator H  20T .