PH
HY 1033
Fall 2011
Exam #3
3 Practice
In class (11 hr. 40 min.. ending 4:40
0 pm) Ihas
Oct. 27
You aree allowed to co
onsult one 8.5””x11” sheet off paper with an
nything writtenn on it in your own hand, and
d to use a calculator, ruler, and
a
pencils or pens Do not
n violate the UF honor cod
de. Answers without
w
the reqquired justificaation or explan
nations will bee counted wrong,
wers will only clarify the exa
am
even iff they are corrrect. You mayy quietly ask me any question after raisi ng your hand,, but my answ
questio
ons. Good luckk!
n air) = 3x108 m/s
m
c(light in
c(sound in classroom aair) = 341 m/s
h = 6.6x10‐34 J/Hz
n(water) = 1
1.33
Q(electron) = 1.6x10‐19 Cou
ulombs
1. What field
d or fields, if any, compo
ose an electromagnetic w
wave? Electric and Maggnetic.
2. Does a chan
nging magnettic flux always produce an induced fieldd, or only if th
here is a cond
ductor presen
nt? Always.
p
is stattionary in a magnetic
m
field
d B. What forrce does it feeel from this field?
3. A charged particle
None. It is stationary relative to the field.
f
wing in a possitive direction in a vertica l wire. Use yo
our right hand
d to
4. An electric current is flow
determine what the maggnetic field produced lookks like and draaw it in a pictture, showingg the
direction off the flux.
s
a situation involvingg Faraday’s Laaw.
5. The figure shows
he bar magnett around so the S pole is to
o the left, andd we move ou
ur hand
6. If we flip th
AWAY from
m the coil of wire
w (moving to
t the right), what else, if anything, will
change in the picture an
nd why?
Nothing elsse changes, since the CHAN
NGE in flux will be the sam
me.
7. What is Bre
ewster’s angle
e for light reflection off a clear
c
lake? taanӨ = n = 1.333 so Ө = Inverse (tan 1.33)) = 53°
8. Which pole
e of the Earth’’s magnet is near
n
the north geographicc pole? South..
9. Does a chan
nging magnettic flux produce an electricc current if thhere is no con
nductor preseent? Explain.
No, there must
m be an ele
ectrically conducting circuit to carry thee flow of elecctrons.
10
0. You rub a plastic
p
straw, charging it, and wave it up
p and down 3 times per seecond. What is the frequency of E‐M
radiation produced? Show calculatio
on. T=1/3 secc so f=1/T=3 H
Hz
11
1. In what parrt of the E‐M spectrum is the
t radiation in the proble m above? Veery long waveelength radio waves.
12
2. The work fu
unction ф is the amount off energy it takkes to pry an electron from
m a metal.
For copper ф = 4.5 eV. What
W
is the lo
owest frequen
ncy light whicch can free an
n electron fro
om copper?
‐19
‐19
‐34
155
1.6x10 Joules and f=E/h so f=4.5x1.6xx10 /6.2x100 = 1.2x10 Hz
E=фq=4.5x1
13
3. What is the
e wavelength of the photon in problem above? Show
w you equations.
8
15
‐7
λ=c/f=3x10 /1.2x10 =2..5x10 m=250
0nm
14
4. What part of
o the E‐M sp
pectrum is the
e photon in problem abovee? Show you
ur logic in casee you got #7 w
wrong. UV
15
5. What physiical property does not change when a light wave entters a block o
of clear glass ffrom air? f
16
6. (2 pts) Which bends mo
ore on diffractting, red or blue light? Whhich bends leess on refractiing, red or blu
ue light?
Red; red
17
7. (5 pts) You take the follo
owing data on
n the photo‐e
electric effectt:
λ = 400 nm
V = 2.0 voltts
V = 1.5 voltts
λ = 530 nm
V = 1.2 voltts
λ = 670 nm
V = 0.9 voltts
λ = 900 nm
Make a neaat graph of E(photon) vs. f((photon). Use your ruler tto get the scaales correct, in
n Joules (y‐axxis) and Hz (x‐‐
axis).
e of the best straight–line fit to the plottted points in
n units of Joule‐sec?
Extra creditt (2 pts): Whaat is the slope
3.40E-019
Photon Energy in Joules
3.20E-019
3.00E-019
SLOPE=4.2E-34 J-s
note: h=6.2E-34 J-s
2.80E-019
2.60E-019
2.40E-019
2.20E-019
2.00E-019
1.80E-019
1.60E-019
1.40E-019
1.20E-019
3.00E+014
4.00E+014
5.00E+014
6.00E+014
7.00E+014
Photon Frequeny in Hz
8.00E+014