phy 112 final
what is the peak electric field strength of an EM wave if the peak magnetic field strength is 0.1T?
E=B/C E=(0.1)/(3E8) E=3E7 N/C
UV
UV spec, a range of EM waves just above human vision
a particular inductor is connected to a circuit where it experiences a change in current of 0.8 amps every 0.10 sec. if the inductor has a self-inductance of 2.0V, what is the inductance?
V=L(di/dt) 2=L(0.8/0.10) L=0.25 H
EMF example
a 20 turn loop w/ 5 cm length is roated in a uniform magnetic field of strength 2.5T. the loop begins so the angle btwn a line drawn perpendicular to the loop area nad the field lines in 90 degrees. the loop rotation ends at angle 0. this rotation takes 7.0ms. the wire is insulated, 4x10^-4 m in diameter, and made of nichrome (p=1.1E-6). what is the current in the wire loops? solve for EMF: e= -N(change in flux/change in time) e= -20((2.5T)(0.05^2)(cos0)-(2.5T)(0.05^2)(cos90))/(7E-3s) e= -17.9V solve for resistance: R=pL/A R= (1.1E-6)(20)(4)(0.05m)/(pi(2E-4m)2) R= 35 solve for current: V=IR (-17.0)=I(35) i= -0.49A the negative gives the direction of the current
polarized
a collection of transverse waves that have uniform polarizations
unpolarized
a collection of transverse waves with random polarization
motor
a device that converts electrical energy to work
generator
a device that converts work into electrical energyq
inductor
a device that exhibits significant self-inductance
define magnetic flux
a measure of the # of field lines that pass through a given area
magnetic flux
a measure of the # of field lines that pass through a given area
which describes a transverse wave?
a wave whose particles oscillate perpendicular to the direction of wave motion
which of the following is a true statement? a. electromagnetic waves deliver an oscillating amt of enery to a given area of space each second b. electromagnetic waves deliever a constant amt of energy to a given area of space each second c. electromagnetic waves deliver a steadily decreasing amt of energy to a given area of space each second d. electromagnetic waves do not deliver energy
a.
which of the following is a true statement? a. magnetic fields cannot have monopolies b. electric fields cannot have monopolies c. both d. neither
a.
which of the following statements regarding radio waves and sound waves is accurate?
a. sound waves are transverse waves b. sound waves and radio waves travel at approx. the same speed c. neither sound waves or radio waves can travel through water d. none of the above d. none of the above
reflection is the best described as
an = < bounce off a barrier
light ray
an arrow used to indicate the direction in which light travels
red light is the result of
an electromagnetic wave w/ a specific wavelength
real image
an image created by real light and can be projected
virtual image
an image created by virtual light & cannot be projected
visible spectrum
athe range of EM waves that are visible to the human eye
the reason why humans cannot see infrared waves is because a. the waves are too short for human eye to detect b. the waves are too long for human eye to detect c. the waves are too fast to detect d. human eyes cannot detect electromagnetic waves
b.
the primary difference between xray waves and radio waves is a. xrays are faster b. xrays are longer c. xray waves are higher frequency d. more than one
c.
which of the following factors will affect the intensity of an EM wave? a. peak electric field stregth b. peak magnetic field stregth c. both d. none
c.
which of the following factors will affect the intensity of an EM wave? a. wavelength b. frequency c. amplitude d. more than one
c.
which of the following is a true statement? a. movement of charge creates magnetic fields b. changes in electric fields create magnetic fields c. both d. none
c.
red light has a wavelength of 6.5x10^-7m. what is the frequency of red light?
c=lambda*f (3E8)=(6.5E-7)(f) = 4.6E14
a particular electromagnetic wave ahs a frequency of 5E17 Hz. what is the wavelength of the wave?
c=lambda*f 3E8=lambda(5E17) =6E-10
a conducting square loop with side lengths of 0.50m is initially in a magnetic field with a strength of 0.5T directed out of the page. the field strength changes to a value of 4.0T during 0.5 seconds. what is the change in flux?
change in flux= (BAcosfinal)-(BAcosinitial) = ((4.0T)(0.50^2))-((0.5T)(0.50^2)) (1)-(0.125) = 0.875 wb what is the induced EMF? emf=change in flux/time = (875wb)/(0.5s) = 1.75V if the total resisitance is of the loop is 20. what is the current in the loop? V=IR (1.75V)=I(20ohm) I=0.0875 amp what is the direction of the current through the resisitor? L-R out of the page
refraction
changing of a light rays direction when the ray passes from one material into a new material
alternating current is the best described as
current that changes direction and changes magnitude
which of the following circuit components will function the same regarless of whether the voltage source is direct or alternating? a. inductors b. transformers c. capacitors d. resistors
d
ampere's circuit law
describes how magnetic fields are created. specifically- magnetic fields are created by moving charges or by changing electric fields
gauss's law of electricity
describes the nature and behavior of elctric field lines- electric field lines move away from (+) towards (-) sources. the electric flux leaving a volume is proportional to the amt charge inside the volume
gauss's law of magnetism
describes the nature and behavior of magnetic field lines. There are no magnetic monopolies (i.e. N pole is always paired with S pole) & the magnetic flux through a closed surface is zero
current is caused by
electric potential differences
huygen's principle
every point on a wave front is source of wavelets that spread out in the forward direction at the same speed as the wave itself. a line drawn tangent to the wavelets is the new wave front
the wave length is the distance measured...
from wave crest to wave crest, from trough to trough, and the length of one complete wave oscillation
qualitatively and quantitatively apply the concepts of induction to explain how generators, motors, transformers and inductors work
generators: -convert work into electric energy- if you roatate a loop in magnetic field, an EMF will form producing current in the loop - can use Faradays law to solve - e=-N(change flux)/(change in time) - field strength and loop stay constant motors: - induced EMF occurs whether you rotate by hand or run current the wire & allow the magnetic force to rotate the loop transformers: - used to change the voltage in a current inductors: - change in flux creates an EMF - if the current that runs through the eolenoid wires is an alternating current, then the magnetic field stregth will fluccuate
x rays
high frequency electromagnetic waves capable of passing through human tissue but not bones
e=-N((change flux)/(change time))
i.e. a 10 turn circular wire loop w/radius of 12 cm is initially in a uniform magnetic field w/a strength of 3.0T. the field decreases to 0 over a time of 0.5 seconds- what is the induced EMF? answer: e= -N(change flux/change time) e= -10(3T)(pi)(0.12^2)/(0.5s) e= 0.86V
quantitatively determine the magnitude of induced EMF & any resulting current in a wire loop
i.e. a bar w/ a length of 25 cm is moved through a 0.5T magnetic field @ a speed of 20m/s. What is the magnitude of the EMF across the bar? the motion is perpendicular to the field direction answer: e=BLvcos0 e= (0.5T)(0.25m)(20m/s) e= 2.5V
EMF problem
i.e. a metal bar is pushed along two neutral parallel rails. the rails are spaced 10 cm apart, and are connected w/a 5.0 resistor the mtal bar is moved @ a constant speedof 1.0m/s towards the resisitor. the system is in the presence of a 3.0T magnetic field. what is the current through the rails if the rails and the bar have negliable resistance? answer: solve for EMF: e=-N(change in flux)/(change in time) e=-BLvcos0 e= -(3.0T)(-0.10m)(1.0m/s)(cos0) e=0.3V solve for current: V=IR (0.3V)=1(5.0) I=0.6A
calculate magnitude and direction of magnetic flux
i.e. what is the flux through a square wire loop that is 10 cm on each sid if it is in a magnetic field w/ a strength of 0.5T? the angle between the field and a line drawn perpendicular to the area is 30 degrees. answer: 0=BAcos0 0=(0.5T)(0.1^2)(cos30) = 0.0043 wb
magnetic field strength problem
if the speed of an elecromagnetic wave is 3E8m/s, what is the magnitude of the electric field when the magnetic field strength is 4ut? answer: C=E/B (3E8m/s)=E/(4E-6T) E= 1200 N/C
a magnetic field oscillates in the +/-z direction, while the electric field oscillates in the +/-y direction. The direction of the wave motion is..
in the x direction
if a magnetic field oscillates in the +/- x plane and the electric field oscillates in the +/- z plane, then the direction f the traveling light wave will be...
in the y plane
a wire loop sits motionless in a uniform magnetic field as shown below (ch9quiz). which of the following changes will induce a clockwise current in the loop?
increase the magnetic field strength
thin film interference
interference from light reflected from different surfaces of a thin flim
current travels to the right through the wores as shown below (ch9quiz). what is the direction of the magnetic field at the position marked by the X?
into the screen ------> x
maxwell-faraday equation
is a combo of faradays law and lenzs law- specifically the magnitude of an induced EMF is proportional to the rate of change of magnetic flux
coherent light
light waves that are in phase with each other or have a definite phase relationship
sound waves
longitudinal waves created by oscillating pressure on some material- requires a medium to travel
radio waves
low frequency electromagnetic radiation, often used as carrier waves for info by oscillating the emitted amplitude or frequency
will wavelength, frequency, or amplitude affect the speed of light through a vacuum?
no
significance of maxwell eq.
one of the most important consequences of these equations is that maxwell showed that electric and magnetic fields are not seperate. these equations also show if the moving charge createing electric and magnetic fields was oscillated, this would create transverse waves in the resulting electric and magnetic fields- this is VERY important
a wire oriented along the vertical edge of the screen has a current moving in the upward direction. if the wire is in a field directed from right to left across the screen, the wire will experience a force directed..
out of the screen
which has the fastest speed?
radio waves, blue light, and x rays have the same speed
wave intensity is defined as
rate of energy delivered to a certain area
wave frequency refers to..
the # of wave oscillations that occur in a second
Lenz's law
the (-) sign in faraday's law that indicated the direction of the induced EMF opposes the direction of the changing flux
the angle of reflection that occurs at a boundary is dependent on
the < of incidence
IR spectrum
the IR spec, heat radiation given off by all objects, a range of frequencies just below human vision
the angle of refraction that occurs at a boundary is dependent on
the angle of incidence, the index of refraction of the inintial material, and the index of refraction of the new material
diffraction
the blending of a wave around corners or edges
refraction is best described as
the change in direction experienced by light passing through a boundary
voltage is best described as
the difference in the enegy per charge ratio btwn teo points in an electric field
focal length
the distance between a curved mirror or lens and its focal point
wave intensity is most closely related to
the energy a wave delivers to a given area every second, the loudness of a sound wave, & the brightness of a light wave
reflection
the equal < bounce of light off a surface
the wave amplitude refers too...
the height of a transverse wave measured from equilibrium to crest ot trough and the max displacement of a particle in a wave from its equilibrium position
critical angle
the incident < that produces a refraction < of 90 degrees
relativistic kinetic energy
the kinetic energy of an object moving at relativistic speeds
magnetism is caused by
the movement of charge
fringe order
the number m of the specific interference pattern as counted from the central maxima
magnification factor
the ratio of image height to object height which is also = to the ratio of image distance to object distance
index of refraction
the ratio of light speed ina vacuum and light speed in a given material
a property of similar triangles is that
the ratios of their side lengths are equal
Faraday's Law
the relationship btwn induced EMF and rate of changing flux
back EMF
the self-induced EMF that opposes the supplied voltage to a motor
relativity
the study of how differenent observers measure the same event
special relativity
the study of relativity in inertial frames of references
lorentz factor
the term by which relativistic differences are determines y=1/root (1-v2c2)
radio waves
transverse EM waves created through the oscillation of change doesnt require a medium to travel
qualitatively and quantitatively describe the postion and characteristic of an image formed using a flat mirror
- a smooth surface allows an observer to see an image - the entire mirror will ne stuck by light and an < = to the incoming angle will be reflected - perpendicular distance between the object (do) and the mirror (di) - in flat mirrir reflections di=do
a 15 turn circular wire loop with a radius of 3.0 cm is initially in a uniform magnetic field with a strength of 0.5 T. The field decreases to zero over a time of 0.20 seconds. what is the induced EMF?
- convert cm to m 3.0 cm=0.03m e=-N(change in flux)/(change in time) e= -15(0.5T)(pi)(0.03m^2)/(0.10) dont actually multiply by pi e= 0.212
explain how electro magnetic waves form and how they travel
- electro magnetic waves form based on frequency nad emission source- the larger the freq. the smaller the wavelength - they all travel at the same , constant speed
qualitatively and quantitativley describe the speed and path of light when light refracts into a new medium
- if light hits a transparent material, some of the light will reflect, but some of the light will pass through the material. when light enters the new material, it will change direction (the change in direction=refraction) - speed of light= 3x10^8 m/s- this will slow as it travels through transparent materials
which of the following will not operate correctly if connected to a circuit that supplies DC current? a. transformer b. conductor c. neither d. both
- transformers they work through magnetic induction which requires a change in flux. the change in flux is achieved by oscilating the current in the primary coil. inductors also work through magnetic induction which requires a change in flux. the inductance is proportional to the current rate of change
what is the peak magnetic field strength of an EM wave if the peak electric field strength is 3500T?
B=E/C B=3500/(3E8) B=1.2E-5
calculate the amplitude of the electric and magnetic fields in an electromagnetic wave
C=E/B c= speed of electromagnetic wave e= amplitude b= magnitude
the direction os the induced current in a wire will be in a direction such that the direction of the magnetic field the current creates will be in the direction opposite of the changing flux
1. identify the direction of the flux (the direction of the magnetic field through the wire loop) 2. decide if the flux is increasing or decreasing. as the loop moves to the right, you have more field lines passing through the loop 3. determine the direction of the changing flux. the flux is into the page and increasing more into the page 4. determine the dirction of the new magnetic field created by current in the wire. the magnetic field will be opposite the change in flux direction 5. use the right-hand curl rule to determine the direction of the current that would result in a magnetic field that is out of the page
maxwell's equations (4)
1. gauss's law of electricity 2. gauss's law of magnetism 3. maxwell-faraday equation 4. ampere's circuit law
qualitatively determine the direction of induced elctromagnetic force (EMF) and any resulting curret in a wire loop
-experiments have shown the amt of EMF induced is directly proportional to the rate of the flux change -slow-moving magnet induces less EMF while a fast moving magnet induces less EMF while a fast moving EMF induces more EMF -EMF is also related to the # of loops in the coil- more loops= larger EMF
calculate the intensity of an EM wave
. = to the power(energy/time) . related to the brightness of the light in that area and is dependent on the amp. of the electric and magnetic waves
an ac circuit with a total resisitance of 20 has an rms current of 10 amp. the circuit wraps around an iron core transistor with 50 loops. the secondary coils, leading to a different circuit, wrap with 25 loops. the secondary circuit has a total resistance of 40. what is the rms current in the secondary circuit?
v1/v2=n1/n2 (IR)(IR)=(N1)(N2) (10.0amp)(20ohm)/(1x40)=(50 loops)/(25 loops) irms= 2.5 amp
gamma waves
very high frequency electromagnetic waves emitted by the nucleus of atoms through nuclear decay processes or nuclear reactions
the electromotive force is most closely relatd to
voltage
incoherent
waves that have no phase relationship
the length of a linear broadcasting atenna is oriented in the y plane. a linear recieving antenna should be oriented in the
y plane
