Phys 1310 Final Practice Test
Useful Numbers:
a0 = 5.291e-11 m
k = 8.99 x 109 Nm2/C2
me = 9.11 x 10-31 kg
mp = 1.67 x 10-27 kg
e = 1.6 x 10-19 C
1eV = 1.6 x 10-19 J
0 = 4 x 10-7 Tm/A
0 = 8.85 x 10-12 C2/Nm2
h = 6.62 x 10-34 Js
 = h/2
hc = 1240 nm eV
Problem 1
Honeybees actively foraging in the fields have been found to be electrically charged, due
largely to air resistance as they fly. Measurements have shown that a honeybee can
acquire an electrostatic charge as great as -93 x 10-12 C (i.e., 93 pC). It is thought this
electrical charge plays a significant role in the pollination process. The bee can detach
grains of pollen from a distance, like a charged comb attracting bits of paper.
(a) Determine how many electrons must be transferred to the bee to produce this
electrostatic charge of 93 pC.
(b) Given that the force required to detach pollen from an avocado stigma is 4.0 x 10 -10
N, find the maximum distance at which the electrostatic force between the bee and the
grain of pollen is sufficient to detach the pollen. Assume that the pollen’s charge is
opposite in sign and equal in magnitude to the bee.
(c) Draw the electric field lines for the bee and avocado stigma. Draw an equipotential
surface around the bee
(d) For an arbitrary closed surface around the bee, what is the net outward flux through
the surface? For an arbitrary closed surface enclosing the bee and the avocado stigma,
what is the net outward flux through the surface? (assume the stigma has the same charge
as the bee.
Problem 2
Two positive charges (+8.0 mC and +2.0 mC) are separated by 300 m. A third charge is
placed at distance r from the +8.0 mC charge in such a way that the resultant electric
force on the third charge due to the other two charges is zero. What is r?
Problem 3 Consider the circuit to the right.
(a) Using Kirchhoff’s Junction and Loop Rules, determine
the current in each resistor.
(b) Determine the potential difference between points a and b.
(c) Determine the power dissipated in the 4 Ω resistor.
Problem 4 Experiments have shown that thought processes in the brain can be affected
if the parietal lobe is exposed to a magnetic field with strength of 1.0 T.
(a) Determine how much current a long, straight wire must carry in order to produce a 1.0
T field at a distance at 0.50 m.
(b) Determine how much current an MRI solenoid must carry in order to produce a 1.0 T
field in its center. Assume that the solenoid is 2.5 m long, 1.0 m in diameter, and is
wound with insulated wires 2.2 mm in diameter.
(c) Assume that pesky bee from problem 1 is flying 1 m directly overhead at a velocity of
5 m/s. Assuming the charge on the bee is negative, what is the direction of the magnetic
field in your head?
vbee
you
Problem 5 To monitor the breathing of a hospital patient, a thin belt is girded around the
patient’s chest. The belt is a 200 turn coil. As the patient inhales, the area encircled by
the coil increases according to the following formula: A(t) = 39.0m2 sin(3.5t) The
magnitude of the Earth’s Magnetic field is 50.0x10-6T and makes an angle of 28 degrees
with the plane of the coil.
(a) Find the flux through the coil as a function of time
(b) Calculate the induced emf as a function of time.
(c) If the resistance of the coil is 4 Ohms, calculate the current induced in the loop as a
function of time.
Problem 5.5 – All the Lenz’s Law problems on the PP doc on Tlearn.
Problem 6 An uncharged capacitor and a resistor are connected in series to a battery
with an open switch. At time t=0s the switch is closed. V=15V, C=20x10-6 F, and
R=4x105 Ohms.
(a)
What is the time constant of the circuit?
(b)
What is the maximum current in the circuit?
(c)
Write out an expression for the charge on the capacitor, Q(t), and the current, I(t),
versus time. Sketch Q(t) and I(t)
Problem 7
A ray of monochraomatic light in air falls on the upper surface of two
parallel- sided slabs of transparent material in air, as shown in the diagram.
Find the angle of refraction  in the lower slab
Problem 8
An object is 10 cm from a concave spherical mirror whose radius is 10 cm.
Describe the image (real or virtual, inverted or erect, magnified or
diminished or the same size) and draw the ray diagram
Problem 9 You have two converging lenses with the same focal length of 10cm
(a) If the lenses are converging, is f positive or negative?
(b) Using just one lens, where would you have to place an object such that the
magnification is –1? Draw the ray diagram
(c) It is often useful in optics to project an upright, real image with a magnification of +1
using two lenses. Using the initial object distance you calculated in part (b), how far
apart would the lenses have to be from each other to achieve a final image with Mtot=+1?
(see figure below) Draw the ray diagram for both lenses.
D=?
image
object
p
Problem 10
A
B)
C)
D)
E)
Monochromatic light of wavelength  is normally incident on a plane
diffraction grating, and three rays of light (A, B, and C) are observed. Of
these three rays
A is the first order, B is the second order, and C is the third order.
B is the first order, and A and C are the second order.
A is the zero order, B is the first order, and C is the second order.
B is the zero order, and A and C are the first order.
A, B, and C are all the first order.
Problem 11 The work function of Cesium is 1.9 eV.
a. What is the maximum wavelength which will emit photoelectrons?
b. What color does this correspond to?
c. What is the stopping voltage for the photoelectrons ejected if light of wavelength
450 nm is used?