PHY 122 homework, continued. (Reading refers to College Physics by OpenStax.)
Sec. 5 - Magnetic Forces and Fields.
Read:
A. 1. (2
pts) An electron is moving in the +x
direction in a magnetic field which also points in the +x direction. Does it feel a force? If so, in what direction?
2. (8) The horizontal conductor shown has a weight per
unit length of .392 N/m, and is in a 3.60 T magnetic field which points into
the page. What current must exist in the
conductor for the tension in the supporting wires to be zero? What is the direction of the current?
ans: .109 amp toward
the right.
B. 1. (2 pts) Consider a stationary charged plastic
ball.
a. Does it
create an electric field? _____ Does it
feel a force in an electric field? _____
b. Does it
create a magnetic field? _____ Does it
feel a force in a magnetic field? _____
2. (8) A long straight wire carries a current of 10 A.
An electron is fired at a speed of 1.0 x 106 m/s parallel to the
wire in the direction of the current, from a point 2.0 cm from the wire. Find the force on the electron, including its
direction.
ans: 1.6 x 10-17 N in the –y direction.
C. 1. (2 pts) Consider a copper wire which has a current
in it.
a. Does it
create an electric field? _____ Does it
feel a force in an electric field? _____
b. Does it
create a magnetic field? _____ Does it
feel a force in a magnetic field? _____
2. (2 pts)
Consider a beam of electrons in a vacuum tube.
a. Does it
create an electric field? _____ Does it
feel a force in an electric field? _____
b. Does it
create a magnetic field? _____ Does it
feel a force in a magnetic field? _____
3. (6) The magnetic field over a certain region is B =
4.00 T in the positive x direction. An
electron moves in this field with a velocity 7.00 m/s in the negative z
direction. Find the force on the
electron, including its direction.
ans: 4.48 x 10-18 N, in the +y
direction
D. 1. (2 pts) What is the
direction of the force on the electron shown?
2. (8) Two parallel wires lie 7.50 cm apart on a
tabletop. They both carry 17.0 A in the
+x direction. Find:
a. The magnitude of the magnetic field, B, at the position
of one wire due to the other.
b. The magnitude of the force per meter on one wire due
to the other.
c. The direction of the force on the wire at the bottom
of the picture.
ans: 45.3 mT, 771 mN, +y
E. 1. (2 pts) Explain why
dropping a magnet on the floor can reduce its magnetization.
2. (8) Ionized atoms move in the +x direction through a
region where both an electric field (not shown) and a magnetic field (in the –z
direction) exist. The forces from these
two fields have opposite directions. For
ions with a certain speed, the two forces are the same size, so they cancel and
allow the ions to go straight. (Ions
with other speeds are pushed to the side and miss entering the final beam. This
is how a beam of ions with a single speed is created in devices such as a mass
spectrometer.) The selected ions have a
charge of +5e, and are moving perpendicular to a .550 T magnetic field at 8.75
km/s.
a. What is
the magnitude of the magnetic force?
b. What is
the direction of the magnetic force?
c. What is
the magnitude of the electric field vector, ?
d. What is
the direction of the electric field vector, ?
ans: 3.85 fN, +y, 4.81 kV/m, -y
Sec. 6 - Induction.
Read: Ch. 22, the rest of section 9.
Ch. 23: sec. 1, 2, first page of 5, 7 & 9.
A. 1. (2 pts) A
step-up transformer is designed to have an output voltage of 2200 V when the
primary is connected across a 110 V source.
If there are 80 turns on the primary winding, how many turns are
required on the secondary? ans: 1600
2. (8) A single, plane wire loop of cross sectional area
8.00 cm2 lies in a plane which is perpendicular to a magnetic field
that increases uniformly from .500 T to 2.50 T in 1.00 s. What is the induced current if the loop's
resistance is 2.00 Ω?
ans: .800 mA
B. 1. (4 pts) A coil has an inductance of 3.00 mH, and the current through it changes from .200 A to 1.50
A in .200 s. Find the magnitude of the
average induced emf in the coil during this time.
ans: 19.5 mV
2. (6) The
solenoid has a radius of 1.20 cm. When
the current is turned on, B in it changes from 0 to .45 T in .0750 s. Find the average emf
induced in the ring during this time.
ans: 2.71 mV
C. A stripe of gold paint is painted around the equator
of a balloon. Its resistance is 2.0 x 10-3 ohm. The balloon's axis is parallel to the earth's
magnetic field, which has a magnitude of 1.1 x 10-4 Tesla here. The balloon is deflated so that its radius
decreases from r = 5.00 cm to r = 3.00 cm in .200 s. Find the average current in the stripe during
this time.
ans: 1.38 mA
D. 1. (3 pts) When the current in a certain coil is
increasing at the rate of 1.20 A/s, it induces an emf
of 96.0 mV in itself. What is the
self-inductance of the coil?
ans: 80.0 mH
2. (7) A solenoid 2.50 cm in diameter and 30.0 cm long
has 300 turns and carries 12.0 A.
Calculate the magnetic flux through the surface of a disk of radius 5.00
cm that is positioned perpendicular and centered on the axis of the solenoid,
as shown.
ans: 7.40x10-6 Wb
E. 1. (2 pts) Will a transformer operate if a
continuously connected battery is used for the input voltage across the
primary? Explain.
2. (8) A loop of wire carries 7.00 A, has a 22.0 cm
radius, and lies in the xy plane. An electron at its center is moving at 3.50 x
105 m/s in the +y direction. Find the magnitude and direction of the force
on this electron.
ans: 1.12 x 10-18 N, -x direction
Sec. 7 - Self Induction.
RL, RC, & LC Circuits.
Read:
(The text does not cover LC circuits. I can refer you to other books if you would
like.)
A. 1. (2 pts.) a. A capacitor is discharged through a
resistor. If you graph current as a
function of time, is there any time where this function actually reaches a
current of zero?
b. A capacitor is discharged through an inductor. If you graph current as a function of time,
is there any time where this function actually reaches a current of zero?
2. (8) When the switch is closed at t = 0, the charge on
the capacitor is 17.0 μC. The charge decreases from there until at t =
100 μs it is 6.16 μC. Find (a) the angular frequency in radians per
second, and (b) the inductance of the coil.
ans: 12 000 rad/s, .278 mH
B. In the circuit shown, E = 20.0 V, C = 6.00 mF,
and R = 2.00 x 106 W. The capacitor starts out uncharged. 7.00 s after the switch is closed, what are
(a) the charge on the capacitor, (b) the voltage across the capacitor, (c) the
voltage across the resistor, and (d) the current in the circuit?
ans: 53.0 mC, 8.83 V,
11.2 V, 5.60 μA
C. 1. (2 pts) As the voltage increases across a
capacitor being charged in an RC circuit, does the current flowing into it
increase, decrease, or stay the same?
2. (8) A 2.50 mF capacitor initially holds 40.0 mC of charge. At t
= 0, it is connected to a 3.00 kW
resistor, and starts discharging through it.
At t = 10 ms, what is
a. the charge
on the capacitor?
b. the
voltage across the capacitor?
c. the
current in the circuit?
ans: 10.5 mC, 4.22 V,
1.41 mA
D. 1. (1 pt) When the circuit
in problem 2, below, reaches its final, steady state, what is the inductance of
the coil?
2. (9) If E = 6.00 V, L = 8.00 mH, and R
= 4.00 Ω,
a. What is the time constant of this circuit?
b. Calculate the current 250 μs after the switch is closed.
c. What is the value of the final, steady-state current?
ans: 2.00 ms, .176 A, 1.50 A
E. 1. (2) a. A capacitor, initially with 15 V across it,
is discharged through a resistor. What
is the voltage across the capacitor after one time constant?
b. An uncharged capacitor is connected, through a
resistor, to a 15 V battery. What is the
voltage across the capacitor after one time constant?
ans: 5.52 V, 9.48 V
2. (8) A 2.50 mF
capacitor initially holds 40.0 mC of
charge. At t = 0, it is connected to a
3.00 mH coil, and starts discharging through it. At t = 1.30 ms,
what is
a. the charge
on the capacitor?
b. the
voltage across the capacitor?
ans: -30.7 mC, -12.3 V
Sec. 8 - A.C. Circuits
Read:
A. Consider a series RLC circuit for which R = 200 Ω, L = 600 mH, and C = 26.5 μF. The applied
voltage has an amplitude of 50.0 V, and a frequency of 60.0 Hz. Find
(a) the amplitude of the current,
(b) the phase angle between the current and the applied voltage,
(c) the amplitude of voltage across the inductor,
(d) the phase angle between the current and the voltage
across the inductor.
ans: 211 mA, v leads by 32.2°, 47.7 V, v leads by 90.0°
B. 1. (1.5 points) An RLC
series circuit is connected to a 120 V AC source. The circuit has a resistance of 10 Ω and an impedance of 20 Ω. What is the
current?
2. (4 points) An RLC circuit
is used in a radio to tune in a station broadcasting at 99.7 MHz. The resistance
in the circuit is 12.0 Ω, and the inductance is 1.40 μH. What
capacitance should be used?
ans: 1.82 pF
3. (4.5 points) The rms output
voltage of an AC generator is 200 V, and the operating frequency is 100
Hz. Assuming a phase angle of zero,
write the equation giving the output voltage as a function of time.
ans: v = (283 V)cos(628t)
C. A generator
drives a circuit as shown. Calculate the
a. inductive
reactance,
b. capacitive
reactance,
c. impedance,
and
d. phase
angle between the current and
generator
voltage.
ans: 78.5 Ω, 1.59 kΩ,
1.52 kΩ,
-84.3°
D. 1. (2 point). An AC ammeter
reads an effective current of 1.00 amps.
What is the value of A on this graph?
2. (8) An RMS current of 4.5 A flows through a 3.0 mH coil when it is connected to a 50 V (RMS), 400 Hz AC
source. What is the coil's internal
resistance?
ans: 8.16 Ω
E. 1. (2 pts) The graph shows how the voltage across an inductor varies
with time. Starting at the same time
this voltage graph does, sketch a graph of the inductor’s current as a function
of time.
2. (2) The frequency in an RLC series circuit is varied
from zero to something quite high. Fill
in a sketch on this graph showing how the current varies as a function of
frequency.
3. (6) A light bulb is connected in series with an inductor
across a household outlet (120 V RMS, 60 Hz).
If the bulb’s resistance is 107 Ω, and the RMS current is .748
A, find (a) the voltage across the bulb, (b) the voltage across the inductor.
ans: 80.0 V, 89.4 V
Sec. 9 - Vibration & Waves.
Read: Ch. 16 sec. 1 – 3 & 9.
A. 1. (2 points) What
exactly happens to the frequency of a harmonic oscillator if you
a. double its
mass?
b. double its amplitude?
2. (8) Two side views of someone surfing are shown. For this wave, what are the following? (a) period, (b) frequency, (c) angular
frequency, (d) wavelength, (e) speed
ans: 12 s, .0833 Hz, .524 rad/s, 30 m, 2.5 m/s
B. 1. (2 points) A wave's
frequency is 5 Hz. What is its period?
2. (8) Suppose that the speed of the wave in the figure
is 5.00 m/s.
a. What is its frequency?
b. Its amplitude?
c. If the frequency is now
doubled, what will be the wavelength of the new wave?
ans: 125 Hz, .10 mm, 2.0 cm
C. 1. (2 points) How do
transverse waves differ from longitudinal waves?
2. (8) When this rope is shaken with a period of .111 s
the resulting wave has a wavelength of 2.66 m.
The rope is 2.00 m long and has a mass of .500 kg. What is the value of the suspended weight,
which is providing the tension in the rope?
ans: 144 N
D.1. (1 point) If a
mass-spring system hanging vertically is oscillating, why does the motion
eventually stop?
2. (3) Light from a helium-neon laser has a wavelength
of 632.8 nm. What is its frequency?
ans: 4.74 x 1014 Hz
3. (6) A simple harmonic oscillator has a spring
constant of 100 N/m. Determine the change
in its period if its mass is changed from 6.00 kg to 6.50 kg.
ans: increases by
.0628 s
E. 1. (1 pt) If a fire siren
went off one mile from your house, does the sound reach you a little sooner in
the summer, a little sooner in the winter, or is there no difference?
2. (1 pt) A heavy rope and a
light rope, both under the same tension, are strung between two masts on a
ship. Sailors on one mast start shaking both
ropes at the same time. Do the waves
reach the other mast sooner on the heavy rope, sooner on the light rope, or is
there no difference?
3. (8) A spring is hung from the ceiling, and a 200 g
object is attached to its lower end. The
1.96 N weight of this object stretches the spring 22.0 cm. If this system is set vibrating, what is its
frequency?
ans: 1.06 Hz
Sec. 10 - Sound.
Standing waves.
Read: Ch 16 sec. 10. Ch. 17 sec 3 & 5.
(The text does not cover the inverse square law for
intensity. I can refer you to other
books.)
A. 1. (2 points) A piano plays a note, then a horn plays the
same note at the same loudness. What is
the difference between these sound waves?
(That is, what is the physical difference between sounds of different
quality?)
2. (8) (a) Calculate the length of a pipe that
has a fundamental frequency of 240 Hz if the pipe is closed at one end and open
at the other. (b) What is its next
resonant frequency above the fundamental?
ans: .357 m, 720 Hz
B. 1. (5 points) A standing wave is established in a 120 cm long
string fixed at both ends. The string
vibrates in four segments when driven at 120 Hz. (a) Determine the wavelength. (b) What is the fundamental frequency of the
string?
ans: 60.0
cm, 30.0 Hz
2. (5) Solar radiation has an intensity of 1340 W/m2 at Earth’s location, 1.50 x
1011 m from the sun. Find the
intensity of solar radiation at the planet Mercury, 5.80 x 1010 m from the sun.
ans:
8960 W/m2
C. 1. (3 pts) The fundamental frequency
of a certain string is 1300 Hz. What is
the highest resonance frequency of the string that can be heard by a person
able to hear frequencies up to 20 000 Hz?
ans: 19 500 Hz
2. (7) A loudspeaker sends out 8.00 watts of power in
the form of sound waves. The speaker is
on top of a tall telephone pole, so the waves spread out uniformly in all
directions. Find
a. the sound
intensity 5.00 m from the speaker.
b. the sound
level there, in decibels.
ans: .0255 W/m2,
104 dB
D. 1. (1 point) Water drips into a bathtub from both the
faucet and the showerhead. At one
particular moment, drips from only the faucet would make the wave shown on the
left. Just drips from the shower would
make the wave on the right. With both
waves present at the same time, what is the displacement of the water’s surface
at the point indicated? Each vertical
division is 1 mm.
2. (1
pt) Either of two loudspeakers produces 50 dB,
corresponding to an intensity of 1 x 10–7 W/m2, by itself. Multiple choice, pick one: If both are
sounded at the same time, there will be
(a) 100 dB and 2 x 10–7 W/m2 (b) 100 dB but not 2 x 10–7
W/m2
(c) 2
x 10–7 W/m2 but not 100 dB (d) neither 100 dB or 2 x 10–7 W/m2
3. (1) If you double your distance from a light source,
what happens to the intensity? (Include
how much it changes, not just a vague “increases” or “decreases.”)
4. (7) A string in a piano is 0.400 m long, has
a mass of 3.00 g, and is under 800 N of tension. What is its fundamental frequency?
ans: 408 Hz
E. 1. (1 point) The picture
shows a string with a standing wave on it, in several of the positions the
string goes through. When in the center
position (flat), is the velocity of point b in the same direction as a’s, in
the opposite direction, or zero?
2. (9) In the afternoon, as 400 cars per minute pass on the highway
outside the window, the sound level in a motel room is 80.0 dB. What is the average sound level in the room
later, when only 65 cars per minute are going by? Assume that the cars are the only significant
source of sound.
ans:
72.1 dB
F. From
now on, each assignment will include review questions. You are just as likely to be given the review
quiz as any of the others.
The
ammeter indicates .100 A flows through it in the direction shown. Find the unknown emf.
ans: 8.00
V
Sec. 11 – Electromagnetic Waves.
Reflection and Refraction.
Read:
Ch. 25 sec. 2
– 4, 6 & 7.
A. 1. (2 pts) Explain the difference
between a real and a virtual image.
(That is, what makes a real image real and what makes a virtual image
virtual.)
2. (8) In a certain video projector, the LCD which acts
as the object is 12.0 cm from the lens.
The image on the screen is 4.00 m away.
(There are actually three LCD panels, one each for red, green and blue,
but let’s not complicate things.)
a. What is
the focal length of the lens?
b. If the LCD is 2.50 cm by 3.50 cm, what
will the dimensions of the image on the screen be?
ans: 11.7 cm, 83.3 cm by 117 cm
B. 1. (1 point) Do radio
waves travel at the speed of sound, or at the speed of light?
2. (1) Which color has the longest visible
wavelength?
3. (2) There are two ways to make an electric
field: 1) An field is
found around a charge and 2) An field is
induced by a changing field.
Make a similar list of the way(s) to make a magnetic field.
4. (6) A 2.0 cm high object is placed 20.0 cm in front
of a concave mirror whose radius of curvature is 60.0 cm. Calculate the image’s position, size and
character (real or virtual? upright or
inverted?).
ans: -60 cm, 6.0 cm,
virtual & upright.
C. A 2.0 cm high object is placed 20.0 cm in
front of a concave mirror whose radius of curvature is 60.0 cm. Use a ray diagram (not equations) to
find the position, size and character of the image.
ans: -60 cm, 6.0 cm, virtual & upright.
D. 1. (2.5
points) State the law of reflection and
illustrate its meaning with a diagram.
2. (3.5) The index
of refraction of a certain material is 1.58.
What is the speed of light in this material?
ans: 1.90
x 108 m/s
3. (4) A beam of light travels from benzene into
water. If the angle of incidence in the
benzene is 48°, what will be
the angle of refraction in the water?
ans: 57°
E. 1. (2 pts) An electromagnetic wave can travel
through empty space, far from any charges or currents. Where do the fields which vibrate as the wave
goes by come from?
2. (8) A light ray is incident at an angle θ on the top surface of a block of polystyrene as shown. Find the maximum angle θ for which the refracted ray undergoes total internal reflection at the
left vertical face of the block if it is immersed in water.
ans: 30.3°
F. (Review)
A loop of wire in a uniform magnetic field rotates 30° as shown. The area of the loop is .180 m2
and B = .0750 T. Find:
a.
the change in flux through the loop.
b. the average emf
induced if the change takes 4.17 ms.
ans:
– .00181 Wb, .434 V
Sec. 12 – Interference.
Read:
A. 1. (5.5 pts) What is the minimum distance
between two points which can be resolved 29 km away using a telescope with a
4.00 cm diameter objective lens? (Assume
λ = 580 nm.)
ans: 51.3 cm
2. (4.5) A material having an index of
refraction of 1.30 is used to coat a piece of glass (n = 1.50). What should be the minimum thickness of this
film if it is to minimize reflection of 500 nm light:
ans: 96.2 nm
B. Light of wavelength 500 nm is incident normally
on a diffraction grating. If the third
order maximum of the diffraction pattern is observed at 32.0°, (a) what is the number of rulings per
centimeter for the grating? (b) Determine the highest order maxima that can be
observed in this situation.
ans: 3.53 x 103, 5
C. 1. (2 pts) An oil film on water appears
brightest at the outer regions where it is thinnest. From this information, what can you say about
the index of refraction of oil relative to that of water?
2. (8) A pair of narrow parallel slits separated
by .250 mm are illuminated by green light (λ
= 546.1 nm). The interference pattern is
observed on a screen 1.20 m away from the plane of the slits. Calculate the distance from the central
maximum to the first bright region on either side.
ans: 2.62 mm
D. 1. (1 point) This is an enlarged
cross-sectional view of a camera lens.
Light reflected from the top of the coating interferes with light
reflected from the bottom. Is the
interference constructive or destructive?
2. (2) As
it evaporates, the thinnest spot on a soap bubble appears black just before it
breaks, indicating the reflected rays are about 180° out of phase. Why doesn’t a path difference of nearly zero make
it 0°? (Shiny
instead of dark?)
3. (7) The second-order bright fringe in a
single slit-diffraction pattern is 1.40 mm from the center of the central
maximum. The screen is 80.0 cm from a
slit of width .800 mm. Calculate the
wavelength.
ans: 560 nm
E. Two speakers are driven by the same
oscillator with a frequency of 200 Hz.
They are located 4.00 m apart on a vertical pole. A man whose ears are level with the lower
speaker walks straight toward it, as shown.
Ignore reflections from the ground.
(a) How many times will he hear a minimum in
sound intensity?
(b) How far from the pole is he at these
moments?
ans: two, 8.90 m & 1.82 m
F. (Review) An electron is near two ionized atoms
as shown. Atom A has lost two electrons,
atom B lost three. If the force on the
electron from atom A is twice the force from B, how far is A from the electron?
ans: 1.91 x 10-9 m
Sec. 13 – Atoms. Solids.
Read:
Ch. 30 sec. 3,
“Lasers” p. 1203 – 1205, sec. 6, just skim sec. 9.
(The text does not cover solids. I can refer you to other books if you would
like.)
A. 1. (2 pts)
Is the center layer of a pnp transistor doped
with donors or acceptors? What about the
outer layers?
2. (2 pts) If matter has a wave nature, why is
this not observable in our daily experiences?
3. (6) An FM radio transmitter has a power
output of 150 kW and operates at a frequency of 99.7 MHz. How many photons per second does the
transmitter emit?
ans: 2.27 x 1030
B. A beam
of electrons is incident on a slit 3.50 nm wide, forming a diffraction pattern
on a screen 20.0 cm beyond. If the first
side maximum is 3.1 cm from the pattern’s center, what is the speed of the
electrons?
ans: 2.04 x 106 m/s
C. 1. (2 pts)
Can the electron in the ground state of hydrogen absorb a photon of
energy (a) 10.0 eV? (b) 14.0 eV?
2. (8) In
hydrogen, when electrons dropping into the ground state give off a 94.96 nm
spectral line, what value of n do they fall from?
ans: 5
D. 1. (3 pts) Light Emitting Diode (LED): Electrons
at the bottom of the conduction band encounter holes at the top of the valence
band at a p-n junction. When they
combine, they release an amount of energy equal to the gap between the two
bands. If the diode releases this energy
as light, rather than heat, it is an LED.
In an LED emitting green light with a wavelength of 520 nm, what is the
gap between the bands?
ans: 3.82 x 10-19 J (or 2.38 eV)
2. (2 pts) A common type of transistor is a pnp or npn sandwich, whose center
layer is very thin. Explain how this
acts as a "valve" for electric current.
3. (5) In the Bohr model of hydrogen, what is
the wavelength of the electron in
a.
The ground state, n = 1? (The atom’s radius is .529 Ǻ.)
b. A
state where n = 2? (The atom’s radius is 2.12 Ǻ.)
ans: 3.32 Ǻ, 6.66 Ǻ
E. 1. (3 pts)
Explain what goes on in a p-n junction that allows current to flow
through it in one direction, but practically stops it from flowing the other
way.
2. (7) The hydrogen lines in the visible part of
the spectrum are those for which the electron falls into the n = 2 level. If light from a hydrogen lamp falls on a CdS crystal (energy gap = 2.42 eV), which of these visible lines are absorbed, and which are transmitted? (Just as in a single atom, an electron in a
solid can only jump from one allowed energy to another.)
ans:
The n = 3 to n = 2 line is transmitted, all others absorbed.
F. (Review)
1. (2 pts) a. In a series RLC circuit, what is
the possible range of values for the phase angle?
b. What is the phase angle when the inductive reactance
equals the capacitive reactance?
2. (8) The
region shown is inside a solenoid 40.0 cm long with 2000 turns. Both the solenoid and the wire inside it
carry 12.0 A. Find the magnitude of the
force on the 3.00 cm straight wire.
ans:
.0136 N
Sec. 14 – Nuclei.
Ch. 31 sec. 1, 3 – 6.
Ch. 32 sec. 2, just skim sec 5 & 6.
A. 1. (2 pts) The decay of 235U to 207Pb (by a series of steps) is used by geologists to date rocks. Rock A contains 5 mg of 235U and 5 mg of 207Pb. Rock
B contains 10 mg of 235U and 20 mg of 207Pb. Rock C contains 30 mg of 235U and 10 mg of 207Pb. Which
is oldest?
2. (8) Using the fact that the atomic mass of 5626Fe is 55.934 940, find its
binding energy per nucleon.
ans: 8.79
MeV/nucleon
B. 1. (2 points) Explain the difference between
radiation sickness and cancer.
2. (8) A
freshly prepared sample of a certain radioactive isotope has an activity of
10.0 mCi.
After 4.00 h, its activity is 8.00 mCi.
a.
Find the half life.
b.
What will the activity be 8.00 h after it was fresh?
ans: 12.4 h, 6.39 mCi
C. 1. (3 pts)
What is an alpha particle? What is a beta particle? What is a gamma ray?
2. (1) By what process does the Sun generate its energy?
3. (6) Determine which decays
can occur spontaneously. Show why each
answer is correct.
(a) 4020Ca
® e+ + 4019K
(b) 9944Ru
® 42He + 9542Mo
(c) 14460Nd
® 42He + 14058Ce
ans: Only (c) can occur.
D. 1. (2 points) The mass of any nucleus is
slightly less than what you get by adding the individual masses of the protons
and neutrons that make it up. Explain
why.
2. (2) What is one difference between a neutron
and a neutrino?
3. (6) Using this graph, estimate the energy
released when a nucleus of mass number 200 is split into two nuclei each of
mass number 100.
ans: about 180 MeV, depending on how you estimate tenths of an MeV on the graph.
E. 1. (2 pts) A sample of an isotope with a
half-life of 5 years presently has an activity of .80 mCi.
Ten years from now, its activity will be
_______mCi. Twenty-five years from now, it will be
_______mCi.
2. (2) What is given off by the fission of
uranium that can go on to cause another fission event?
3. (6) Fill in the blanks for the unknown
nuclide X, and answer the question.
(a) Is
X also a Ni nucleus?
(b) Is
X also a Po nucleus?
(c) Is X
also a Pb nucleus?
ans: yes, no, no.
F. (Review) 100 m from the speakers, the sound level at an outdoor
concert is 90.0 dB.
Assuming open space in between, how many decibels are there outside a
home 5000 m away? (A little over three
miles.)
ans: 56.0
dB