Physics: Principles and Problems
Physics: Principles and Problems
9th Edition
Elliott, Haase, Harper, Herzog, Margaret Zorn, Nelson, Schuler, Zitzewitz
ISBN: 9780078458132
Textbook solutions

All Solutions

Page 718: Assessment

Exercise 30
Step 1
1 of 2
Exercise scan
Result
2 of 2
The empty fields are filled from left to right as $E$, $B$ and $c$.
Exercise 31
Step 1
1 of 2
mass = m = $9.11times 10^{-31} Kg$

Charge = q = $1.6 times 10^{-19} C$

Result
2 of 2
m = $9.11times 10^{-31} Kg$

q = $1.6 times 10^{-19} C$

Exercise 32
Step 1
1 of 2
Isotopes are atoms that have the same number of protons but different number of neutrons i.e. a different atomic mass.
Result
2 of 2
Isotopes have the same number of protons but different number of neutrons in their nuclei.
Exercise 33
Step 1
1 of 2
A magnetic field will be always induced at $90^circ$ from the electric field that induces it.
Result
2 of 2
$$
90^circ
$$
Exercise 34
Step 1
1 of 2
AC generators provide time dependent electric fields which create changing magnetic field and so on. DC generators are able to create changing electric fields only when turned on or off.
Result
2 of 2
AC generates changing electric field all the time and DC only when switched on or off.
Exercise 35
Step 1
1 of 2
Exercise scan
Result
2 of 2
The antenna creates electric and magnetic fields that are perpendicular at each other at all times of propagation and mutually induce themselves.
Exercise 36
Step 1
1 of 2
Due to a physical phenomenon called electrostriction quartz crystal will change it’s shape when an electric field is applied. If we now vary the electric field, the crystal will shrink and expand periodically, i.e. it will oscillate.
Result
2 of 2
Electrostriction causes quartz crystal to vibrate.
Exercise 37
Step 1
1 of 2
This is achieved by setting the capacitance of the antenna to desired frequencies. Then, upon receiving the signal, the resonance occur which is then transformed into the maximal signal.
Result
2 of 2
The capacitance of the antenna set to a proper frequency selects the same of the frequency of the signal.
Exercise 38
Step 1
1 of 2
Since electrons are negatively charged, they will be attracted by the positively charged plate so if we want electrons to deflect up, the top plate has to be charged positively.
Result
2 of 2
Top-plate should be charge positively.
Exercise 39
Step 1
1 of 2
To answer this question we are going to use the right-hand rule which tells us that negatively charged particles will bend down only if the magnetic field is pointing into the page.
Result
2 of 2
Into the page.
Exercise 40
Step 1
1 of 2
To solve this problem let’s write the ratio of the electric and the magnetic field in terms of extended SI units

$$
frac{E}{B}=frac{frac{textrm{N}}{textrm{C}}}{frac{textrm{N}}{textrm{A}cdot textrm{m}}}
$$

$$
frac{E}{B}=frac{textrm{A}cdottextrm{m}}{textrm{C}}=frac{textrm{C}cdottextrm{m}}{textrm{C}cdottextrm{s}}
$$

Which finally gives

$$
boxed{frac{E}{B}=frac{textrm{m}}{textrm{s}}}
$$

Q.E.D.

Result
2 of 2
$$
frac{E}{B}=frac{textrm{m}}{textrm{s}}
$$
Exercise 41
Step 1
1 of 2
Since ionized neon atoms are positively charged the right-hand rule tells us that the magnetic field has to point out of the page in order to bend the beam clockwise.
Result
2 of 2
The magnetic field will point out of the page.
Exercise 42
Step 1
1 of 2
If by undeflected we assume particles that do not reach the film plate, then we have to change the signs of the fields simultaneously or not to change them at all. Other wise, if we change only one field sign the particles will again land on the film plate.
Result
2 of 2
Either we change both or none of directions.
Exercise 43
Step 1
1 of 2
According to the well-known EM spectra we have that:

a) Longest wavelengths belong to radio waves.

b) The highest frequencies belong to X-rays.

c) They all travel with the same speed, the speed of light.

Result
2 of 2
a) Radio waves

b) X-rays

c) All have the same speed, $c$.

Exercise 44
Step 1
1 of 2
The channel 2 frequency is smaller, thus its wavelength is longer and requires longer antenna.
Result
2 of 2
Channel 2
Exercise 45
Step 1
1 of 2
The microwaves have a longer wavelengths relative to the visible light, therefore they have a larger eyes.
Result
2 of 2
larger
Exercise 46
Step 1
1 of 2
In order to solve this problem we are going to start from the equation that relates the electric and magnetic field

$$
E=vB
$$

From which we express the magnetic field as
$B=frac{E}{v}=frac{5.8times 10^3}{3.6times 10^4}$
Finally,

$$
boxed{B=0.16textrm{ T}}
$$

Result
2 of 2
$$
B=0.16textrm{ T}
$$
Exercise 48
Step 1
1 of 2
In order to solve this problem we are going to use Newton’s second law which says that on a circular path it has to hold that

$$
qvB=frac{mv^2}{r}
$$

From here, we can express the radius to have that

$$
r=frac{mv}{qB}=frac{1.67times 10^{-27}times 5.4times 10^4}{1.6times 10^{-19}times 0.06}
$$

Finally, we have that

$$
boxed{r=9.4times 10^{-3}textrm{ m}}
$$

Result
2 of 2
$$
r=9.4times 10^{-3}textrm{ m}
$$
Exercise 49
Step 1
1 of 2
In order to solve this problem, we are going to use Newton’s second law which says that on a circular path it has to hold that

$$
qvB=frac{mv^2}{r}
$$

However, we have to find the speed first. We can do this by employing the conservation of energy which says

$$
frac{mv^2}{2}=qV
$$

So we get that

$$
v^2=frac{2qV}{m}
$$

Now, we obtain that

$$
qB=frac{m}{r}cdotsqrt{frac{2qV}{m}}
$$

which gives that the magnetic field is given as

$$
B=sqrt{frac{2mV}{qr^2}}=sqrt{frac{2times9.11times 10^{-31}times 4.5times 10^3}{1.6times 10^{-19}times 5^2times 10^{-4}}}
$$

Which finally gives that

$$
boxed{B=4.5times 10^{-3}textrm{ T}}
$$

Result
2 of 2
$$
B=4.5times 10^{-3}textrm{ T}
$$
Exercise 50
Step 1
1 of 2
Since we are talking about a mass-spectrometer, we are going to use charge-to-mass ratio to solve this problem. By definition, it is given that

$$
frac{q}{m}=frac{2V}{r^2B^2}
$$

From which mass can be expressed as

$$
m=frac{qr^2B^2}{2V}=frac{2times 1.6times 10^{-19}times 8^2times 10^{-4}times 0.077^2}{2times 156}
$$

Finally, one gets that

$$
boxed{m=3.9times 10^{-26}textrm{ kg}}
$$

Result
2 of 2
$$
m=3.9times 10^{-26}textrm{ kg}
$$
Exercise 51
Step 1
1 of 2
In order to solve this problem, we are going to use Newton’s second law which says that on a circular path (and in a magnetic field a moving charged particle will follow such a path) it has to hold that

$$
qvB=frac{mv^2}{r}
$$

a) From here, one can express the speed as

$$
v=frac{qrB}{m}=frac{2times 2times 1.6times 10^{-19}times 0.15}{6.6times 10^{-27}}
$$

Finally, we have that

$$
boxed{v=1.45times 10^7frac{textrm{ m}}{textrm{ s}}}
$$

b) The kinetic energy is to be found via its standard expression

$$
K=frac{mv^2}{2}=frac{6.6times 10^{-27}times 1.45^2times 10^{14}}{2}
$$

Which gives that

$$
boxed{K=6.9times 10^{-13}textrm{ J}}
$$

c) Now, the potential difference that corresponds to that energy is found from

$$
K=qV
$$

$$
V=frac{6.9times 10^{-13}}{2times1.6times 10^{-19}}
$$

Eventually, we get

$$
boxed{V=2.2 times 10^6textrm{ V}}
$$

Result
2 of 2
$$
textrm{a) }v=1.45times 10^7frac{textrm{ m}}{textrm{ s}}
$$

$$
textrm{b) }K=6.9times 10^{-13}textrm{ J}
$$

$$
textrm{c) }V=2.2 times 10^6textrm{ V}
$$

Exercise 52
Step 1
1 of 2
In order to achieve that level of differentiation, one has to be able to distinguish between two molecules one having $175times 10^3$ proton masses and and one having $175times 10^3+1$ proton masses. Percentage wise, the sensibility of such a device could be written as

$$
S=(1-frac{175times10^3}{175times10^3+1})times 100
$$

Which gives that

$$
boxed{S=0.0006%}
$$

Result
2 of 2
$$
S=0.0006%
$$
Exercise 53
Step 1
1 of 2
In order to solve this problem we are going to use the charge-to-mass formula that is used in a mass spectrometer

$$
frac{q}{m}=frac{2V}{r^2B^2}
$$

Here we see that $mpropto r^2$ so we can write

$$
frac{m_1}{m_2}=frac{r_1^2}{r_2^2}
$$

which gives us that the mass of the second isotope is

$$
m_2=m_1times frac{r_2^2}{r_1^2}=28m_ptimes frac{0.1797^2}{0.1623^2}
$$

Which finally gives that

$$
boxed{m_2=34m_p}
$$

Result
2 of 2
$$
m_2=34m_p
$$
Exercise 54
Step 1
1 of 2
It is required that the length of an antenna is comparable to the wavelength of the detected wave. Moreover, there is a standard that they should be half-a-wavelength long son in our case the antenna will be 1cm long.
Result
2 of 2
The antenna should be 1cm long.
Exercise 55
Step 1
1 of 2
In order to solve this problem we are going to use the wavelength formula which says that

$$
lambda=frac{c}{f}=frac{3times 10^8}{66times 10^6}
$$

Which gives that

$$
lambda=4.5textrm{ m}
$$

Now, the distance between the bars of the antenna is

$$
d=frac{lambda}{4}=frac{4.5}{4}
$$

Finally,

$$
boxed{d=1.1textrm{ m}}
$$

Result
2 of 2
$$
d=1.1textrm{ m}
$$
Exercise 56
Step 1
1 of 2
In order to solve this problem we are going to use the frequency formula which says that

$$
f=frac{c}{lambda}=frac{3times 10^8}{650times 10^{-9}}
$$

Which gives that

$$
boxed{f=4.6times 10^{14}textrm{ Hz}}
$$

Result
2 of 2
$$
f=4.6times 10^{14}textrm{ Hz}
$$
Exercise 57
Step 1
1 of 2
In order to solve this problem we are going to use the wavelength formula which says that

$$
lambda=frac{c}{f}=frac{3times 10^8}{101.3times 10^6}
$$

Which gives that

$$
lambda=2.96textrm{ m}
$$

Now, the optimum length of the antenna is $d=frac{lambda}{2}$

$$
d=frac{lambda}{2}=frac{2.96}{2}
$$

Finally,

$$
boxed{textrm{d=1.48textrm{ m}}}
$$

Result
2 of 2
$$
textrm{d=1.48textrm{ m}}
$$
Exercise 59
Step 1
1 of 2
In order to solve this problem we are going to use the wavelength formula which says that

$$
lambda=frac{c}{f}=frac{3times 10^8}{8times 10^8}
$$

Which gives that

$$
lambda=0.375textrm{ m}
$$

Now, the optimum length of single-end antennas is $d=frac{lambda}{4}$ as given in the problem

$$
d=frac{lambda}{4}=frac{0.375}{4}
$$

Finally,

$$
boxed{d=0.0938textrm{ m}}
$$

Result
2 of 2
$$
d=0.0938textrm{ m}
$$
Exercise 60
Step 1
1 of 2
In order to solve this problem we are going to divide the mass of an oxygen atom with the mass of one amu. We have that

$$
N=frac{2.7times 10^{-26}}{1.67times 10^{-27}}
$$

$$
boxed{N=16textrm{ amu}}
$$

Result
2 of 2
$$
N=16textrm{ amu}
$$
Exercise 61
Step 1
1 of 2
In order to solve this problem we are going to use the wavelength formula which says that

$$
lambda=frac{c}{f}=frac{3times 10^8}{94.5times 10^6}
$$

Which gives that

$$
lambda=3.17textrm{ m}
$$

Now, the optimum length of an antenna is $d=frac{lambda}{2}$

$$
d=frac{lambda}{2}=frac{3.17}{2}
$$

Finally,

$$
boxed{d=1.59textrm{ m}}
$$

Result
2 of 2
$$
d=1.59textrm{ m}
$$
Exercise 62
Step 1
1 of 2
In order to solve this problem, we are going to start from the fact that in one-end antennas the optimum length of the antenna is

$$
d=frac{lambda}{4}
$$

So we can express the wavelength as

$$
lambda=4d
$$

On the other hand, the frequency is given as

$$
f=frac{c}{lambda}=frac{c}{4d}=frac{3times 10^8}{4times 0.083}
$$

Finally, we have that

$$
boxed{f=9.04times 10^8textrm{ Hz}}
$$

Result
2 of 2
$$
f=9.04times 10^8textrm{ Hz}
$$
Exercise 63
Step 1
1 of 2
In order to solve this problem we are going to use the charge-to-mass formula that is used in a mass spectrometer

$$
frac{q}{m}=frac{2V}{r^2B^2}=frac{2times 150}{0.098^2times50^2 times 10^{-6}}
$$

Finally, the charge-to-mass ratio is

$$
boxed{frac{q}{m}=12.5times 10^{6}frac{textrm{ C}}{textrm{ kg}}}
$$

Result
2 of 2
$$
frac{q}{m}=12.5times 10^{6}frac{textrm{ C}}{textrm{ kg}}
$$
Exercise 64
Step 1
1 of 2
In order to solve this problem, we are going to use the given formula that tells us that the velocity of the target is given as

$$
v_{target}=frac{cf_{Doppler}}{2f_{transmitted}}=frac{3times 10^8times 1850}{2times 10.525times 10^9}
$$

Which finally gives that

$$
boxed{v=26.4frac{textrm{m}}{textrm{s}}}
$$

Result
2 of 2
$$
v=26.4frac{textrm{m}}{textrm{s}}
$$
Exercise 65
Step 1
1 of 2
The vision, per definition means that some light is being absorbed by the retina and some light is being scattered. However, any absorption of light would destroy invisibility so if the man is truly invisible he cannot see and vice versa.
Result
2 of 2
The invisibility means an absolute lack of light absorption.
Exercise 66
Step 1
1 of 2
In order to solve this problem and to design this experiment we are going to start with the formula for charge-to-mass ratio of a mass spectrometer that relates the magnitude of the magnetic field and the potential difference

$$
frac{q}{m}=frac{2V}{r^2B^2}
$$

So we can express the radius as

$$
r=sqrt{frac{2mV}{qB^2}}
$$

Since we know that our detector has the spacing $d=0.1times 10^{-3}$ m we have that

$$
d=2times(r_{176}-r_{175})=2times(sqrt{frac{2m_{176}V}{qB^2}}-sqrt{frac{2m_{175}V}{qB^2}})
$$

Which after we transfer the masses into proton masses gives

$$
d=2timessqrt{frac{2m_pV}{qB^2}}(sqrt{176}-sqrt{175})
$$

Therefore, if we take that $V_{min}=500$ V we can express $B$ as

$$
B=2timesfrac{sqrt{2Vm_p}(sqrt{176}-sqrt{175})}{dsqrt{q}}=2timesfrac{sqrt{2times 500times1.67times 10^{-27}}(sqrt{176}-sqrt{175})}{0.1times 10^{-3}times sqrt{1.6times 10^{-19}}}
$$

Finally, the magnetic field should be

$$
boxed{B=2.4textrm{ T}}
$$

Result
2 of 2
$$
B=2.4textrm{ T}
$$
Exercise 67
Step 1
1 of 2
Remote controls are electronic devices used for distant command giving and communication with various electronic devices. Usually, they operate by utilizing a broad range of infra-red (IR) part of the EM spectrum. More precisely, it is said for them to belong to CIR or consumer IR devices. They function in the following way: the signal transmitted between the remote and the device controlled by it is usually coded via short pulses of the infrared light. This signal is normally sent to the device via the transmitter part of the remote, usually a LED (light emitting diode). The device is programmed to perform certain actions upon detecting a specific IR light pulse pattern (each button on the remote is coded differently) and therefore after we give the command via remote the device executes it consequently.

The number of remote controls flourished in the last decades with the average US household having as many as four remotes. The reason for this is exactly the one given in the problem, since the IR spectrum is broad enough many devices can be uniquely coded and it is not likely to have interference. However, with their number still increasing, the mentioned interference becomes a plausible option. Therefore, some tweaks have been made to reduce the number of IR controls. One of them is the existence of universal IR remotes. Second is, IR remote via smartphones, a very popular option nowadays.

Result
2 of 2
Remote controls operate by employing a broad spectrum of IR light.
Exercise 68
Step 1
1 of 2
In order to solve this problem we will use the formula for the width of the slit and position of the first minimum

$$
a=frac{L}{y_1}lambda
$$

Where $L$ is the distance to the screen. After we plug in the values

$$
a=frac{0.95}{8.5times 10^{-3}}times 633times 10^{-9}
$$

Finally, the width of the slit is

$$
boxed{a=71times 10^{-6}textrm{ m}}
$$

Result
2 of 2
$$
a=71times 10^{-6}textrm{ m}
$$
Exercise 69
Step 1
1 of 2
Befor connecting the spheres:

$F = dfrac{K (4q) (2q)}{r^2}$

$F = dfrac{8 K q^2}{r^2}$

The total charge on the spheres is:

$q_{net} = q_1 + q_2 = (-4q) + (2q) = -2q$

After connecting the spheres, charges on each of the spheres is the half of the $q_{net}$:

$q’_1 = q’_2 = -q$

The force between them:

$F’ = dfrac{K q_1 q_2}{r^2}$

$= dfrac{K q^2}{r^2}$

$$
= dfrac{1}{8} F
$$

Result
2 of 2
$$
dfrac{1}{8} F
$$
Exercise 70
Step 1
1 of 2
In order to solve this problem we are going to use the definition of the the electric field

$$
E=frac{Delta V}{Delta x}=frac{45}{0.012}
$$

Finally, we get that

$$
boxed{E=3.8times 10^3 frac{textrm{V}}{textrm{m}}}
$$

Result
2 of 2
$$
E=3.8times 10^3 frac{textrm{V}}{textrm{m}}
$$
Exercise 71
Step 1
1 of 2
In order to solve this problem we are going to use the formula for calculating the instantaneous power which is given as

$$
P=IV
$$

$$
P=120times 245=2.94 textrm{ kW}
$$

Since the compressor is operating one quarter of the time the daily cost is now given as

$$
textrm{cost}=Pttimes 0.095=2.94times 6 times 0.095
$$

Finally, we have that

$$
boxed{textrm{cost}=1.68$}
$$

Result
2 of 2
$$
textrm{cost}=1.68$
$$
Exercise 72
Step 1
1 of 2
In order to solve this problem, one should apply the equation of the force on a conductor in a magnetic field

$$
F=IBL
$$

From here we can express the magnetic field as

$$
B=frac{F}{IL}=frac{0.55}{7.7times4.4}
$$

So finally we have that

$$
boxed{=16times 10^{-3}textrm{ T}}
$$

Result
2 of 2
$$
B=16times 10^{-3}textrm{ T}
$$
Exercise 73
Step 1
1 of 2
In order to solve this problem we are going to use the right hand rule that tells us that if the wire is moving east in a magnetic field pointing down/into the page than the current will flow north.
Result
2 of 2
The current will flow north.
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