Download It`s Shocking

Jeopardy (cp)
Subterm 2 Review
Topics Covered:
Waves
Sound
Electrostatics
Circuits
Magnetism
Relativity
The Motion of the Ocean
A cork on the surface of a pond bobs up and
down two times per second on ripples having a
wavelength of 8.50 cm. What is the cork’s
speed?
  0.085m
f  2Hz
v  f  (2Hz)(0.085)
v  0.17m / s

The Motion of the Ocean
If the speed of a wave stays the same, what
happens to the frequency as the wavelength
decreases?
The frequency will
INCREASE.
V=f
The Motion of the Ocean
Mrs. Wright sings toward a cliff in the mountains
and the sound is reflected directly back to her.
She is standing 170 m from the natural wall. If
her music is traveling through air at 340 m/s,
how long will it take Mrs. Wright to hear her
own echo?
v  340m / s
d  170m  2  340m
t?
d
d
340m
v t 
 1.0 sec
t
v 340m / s
Hear the Music
A rather noisy typewriter produces a sound
intensity of 1 x 10-5 watts/m2. Find the
decibel level of this machine.

105 w / m 2
7
 10 log 12
 10 log 110
2
10 w / m
 70 dB

Hear the Music
During the Macy’s Thanksgiving Day Parade it is
5oC outside. A late parade watcher drives
towards the parade at 15 m/s as the parade
marches towards her, at 5 m/s. If one of the
bands plays a note of 415 Hz, what frequency
will she hear? (assume the speed of sound is
334 m/s at 5oC)
 vwave vobserver 
 33415 
  415
  440Hz
f ' f 
 3345 
 vwave vsource 
Hear the Music
A 4.00 m long pipe is half way submerged in
room temperature water where the speed of
sound is 343m/s in the room. What is the
fundamental frequency of the pipe?
1
 = 4L
L 
4
v
v
343m / s
f  

 42.9Hz
 4L 4(2.00m)


It’s Shocking!
• What do the electric field lines look like
for the following charge:
It’s Shocking!
Two point charges of -1.0 nC and +2.0 nC
are separated by a distance of 0.30 m. What
is the electric force on each particle?
(remember 1nC = 1x10-9 C)
9
9
9
kQ1Q2 (9 10 )(110 )(2 10 )
7
F

 2.0 10 N
2
2
d
(0.3)
It’s Shocking
An uncharged conductor is supported by an insulating
stand. A positively charged rod is brought near
the left end of the conductor. The you touch the
right side of the conductor with your hand. The
What is the charge of the conductor now?
NEGATIVE
It’s Shocking
An electric field of 2.0x104N/C is directed along
the positive x-axis. What is the electric force on
an electron in this field? (Qelectron = 1.6x10-19C)
F  QE  (1.6 10 )(2.0 10 )  3.2 10 N
19
4
Along the negative x-axis
15
It’s Shocking
What is the magnitude and direction of
the electric field at a distance of 3.20
m from a –50.0 nC charge?
kQ (9 10 )(50 10 )
E 2 
 43.9N /C
2
d
(3.2)
9
9
It’s Shocking
Two point charges are 4 cm apart. They are
moved to a new separation of 2 cm. By what
factor does the resulting mutual force between
them change?
1) ½
2) 2
3) ¼
4) 4
5) depends on
the charges
kQ1Q2
F
d2
It’s Shocking
Charge A has 10 electric field lines coming
out, Charge B has 20 lines coming out, and
charge C has 30 lines coming in. Which pair
of these charges will have the largest
force between them if placed 1 cm apart?
Charge A
10 lines
Charge B
20 lines
Charge C
30 lines
It’s Shocking
A negative rod is used to give an electroscope a
negative charge. What type of charging is this?
It’s Shocking
• The leaves of a negative electroscope
will stick out. What happens to the
leaves when another negative rod is
brought close to the scope, but does not
touch it?
More negatives
- - - - - - - -
are pushed into
the leaves and
the leaves stick
out even further.
Viva la resistance
What type of wire makes the best conductor?
• Long or short
• Thick or thin
• Rubber or Aluminum
Viva La Resistance
When resistors are put in series, their
overall resistance is
a. Larger than that of any individual resistor
b. The same as the resistance of one of the
resistors
c. Smaller than the resistance of any of the
resistors
Viva La Resistance
A wire 5.0 m long and 3.0 mm in diameter has a
resistance of 100 W. A 15 V potential
difference is applied across the wire. What is
the current in the wire?
V  IR
V 15
I 
 0.15A
R 100
Viva La Resistance
What is the resistance of a 100. W light bulb if it
is plugged into a 120. V outlet?
V
P
R
2
120
100 
R
R  144W
2
Viva La Resistance
Three resistors with resistance of 6 W, 12 W, and 24 W
are connected in series. What is the total resistance
of the circuit?
Rtotal  612 24  42W
Viva La Resistance
• What is the same in a parallel circuit?
Viva La Resistance
Three resistors with resistance of 6.0 W, 12 W, and 24 W
are connected in series with a 12V battery. What is
the current through the 12 W resistor?
The current is the
same through all
of them so the total
resistance must
be used.
V  IR
12  42I
I  0.29A
Viva La Resistance
What is the current through each of the
resistors? (Don’t raise your hand until
you have all THREE resistances)
6W
12 W
6W
12 V
6W
12 V / 6 W = 2 A
6W
12 V / 18 W = 0.67 A
12 W
12 V / 18 W = 0.67 A
Opposites Attract
• What is the direction of the force on the
electron?
.
. .
.
.
.
.
.
.
Opposites Attract
What does the magnetic field look like for
a loop of wire with a clockwise current
as shown?
Into the board
inside the
loop, out of
the board
outside the
loop
X
X
X
X
Opposites Attract
An electron moves with a speed of 7.0 x 106 m/s along
the +x axis. It enters a region where there is a
magnetic field of 2.5 T, directed at an angle of 60 to
the +x axis and lying in the xy plane. Calculate the
magnetic force of the electron.
F  QvB sin   (1.6 10 )(7 10 )(2.5)(sin 60 )
19
F  2.4210 N
12
6
Opposites Attract
A proton is released such that its initial velocity is from right
to left across this page. The proton's path, however, is
deflected (by a force) in a direction toward the bottom
edge of the page due to the presence of a uniform magnetic
field. What is the direction of this field?
Opposites Attract
A generator is created by moving a 0.300 m
long wire in an external magnetic field of 5.50
T at a speed of 15.0 m/s.
(a) What EMF is produced by the generator?
(b) What effective emf if produced by the
generator?
(a)
(b)
EMF  BLv sin 
 (5.5T )(0.30m)(15m / s )  24.75  24.8V
Veff  0.707Vmax  0.707(24.75)  17.5V
Everything’s Relative
Einstein’s theory of relativity is based in part
on which one of the following postulates?
1.
2.
3.
4.
Mass and energy are equivalent.
Space and time are absolutes.
Energy is conserved only in elastic collisions.
Speed of light in a vacuum is the same for all
observers regardless of velocity
5. Speed of light in a vacuum is the same at any
wavelength.
Everything’s Relative
• A rocket ship is 80.0 m in length, when
measured before leaving the launch pad. What
would its velocity be if a ground observer
measured its length as 60.6 m while it is in
flight?
L  Ls 1   v / c
2
2

60.6m  80.0m 1  v
v  0.652c
2
Everything’s Relative
A knight on horseback holds a 10.-m lance. The horse
can run at 0.70 c. How long will the lance appear to a
person that is standing still on the ground as the horse
runs past?
L  Ls 1 v /c
2
L  10m 1 0.7
L  7.1m
2
2

Everything’s Relative
A muon formed high in the Earth’s atmosphere travels
at a speed of 0.990 c for a distance of 4.60 km (as we
see it from Earth) before it decays. Observers on Earth
believe it takes the muon 1.55x10-5 seconds to reach
Earth’s surface. How long does it take in the frame of
the muon??
ts  t 1 (v 2 /c 2 )
ts  1.55 10
5
1 .99
ts  2.18 106 sec

2
Teams, Place Your Bets
Final Jeopardy
• What is the current in the 10 W resistor?
1
Rparallel
1 1 1 6 10 15
   
10 6 4
60
60
Rparallel 
 1.94W
31
Rtotal  1.94  2  3.94W
V
12

I total 

 3.05A
Rtotal 3.94
Vparallel  IRparallel
Vparallel  (3.05)(1.94)
Vparallel  5.91V
Vparallel
I10W 
R10W
I10W
5.91

 0.59A
10