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Question
A light emitting diode emits light when:A) electrons are excited from the valence to the conduction band
B) electrons from the conduction band recombine with holes from the valence band
C) electrons collide with atoms
D) electrons are accelerated by the electric field in the depletion region
E) the junction gets hot
Answer
This answer is hidden. It contains 1 characters.
Related questions
Q:
The intensity of the microwave background radiation, a remnant of the big bang:
A) is greatest in directions toward the center of the galaxy
B) is least in directions toward the center of the galaxy
C) is proportional to the reciprocal of the distance from us
D) is proportional to the square of the distance from us
E) is nearly the same in all directions
Q:
The velocities of distant objects in the universe indicate that the time elapsed since the big bang is about:
A) 105y
B) 1010y
C) 1015y
D) 1020y
E) 1025y
Q:
In terms of quark content a beta decay can be written:
Q:
The quark content of a proton is:
A) uuu
B) uud
C) udd
D) ddd
E) uds
Q:
The up quark u has charge +2e/3 and strangeness 0; the down quark d has charge -e/3 and strangeness 0; the strange quark s has charge -e/3 and strangeness -1. This means there can be no baryon with:A) charge 0 and strangeness 0B) charge -eand strangeness -1C) charge +eand strangeness -1D) charge +eand strangeness -2E) charge 0 and strangeness -2
Q:
A baryon is a combination of:
A) three quarks
B) two quarks and an antiquark
C) one quark and two antiquarks
D) one quark and one antiquark
E) two quarks
Q:
Any meson is a combination of:
A) three quarks
B) two quarks and an antiquark
C) one quark and two antiquarks
D) one quark and one antiquark
E) two quarks
Q:
Quarks are the constituents of:
A) all particles
B) all leptons
C) all strongly interacting particles
D) only strange particles
E) only mesons
Q:
The color theory explains why quarks:
A) form particles in pairs and triplets
B) have charge that is a multiple of e/3
C) have spin
D) have mass
E) none of the above
Q:
The two basic interactions that have finite ranges are:
A) electromagnetic and gravitational
B) electromagnetic and strong
C) electromagnetic and weak
D) gravitational and weak
E) weak and strong
Q:
Strangeness is conserved in:
A) all particle decays
B) no particle decays
C) all weak particle decays
D) all strong particle decays
E) some strong particle decays
Q:
When a kaon decays via the strong interaction the products must include a:
A) baryon
B) lepton
C) strange particle
D) electron
E) neutrino
Q:
Two baryons interact to produce pions only, the original baryons disappearing. One of the baryons must have been:
A) a proton
B) an omega minus
C) a sigma
D) an antiparticle
E) none of these
Q:
In a photoelectric effect experiment at a frequency above cut off, the stopping potential is proportional to:
A) the energy of the least energetic electron before it is ejected
B) the energy of the least energetic electron after it is ejected
C) the energy of the most energetic electron before it is ejected
D) the energy of the most energetic electron after it is ejected
E) the electron potential energy at the surface of the sample
Q:
In a photoelectric effect experiment at a frequency above cut off, the number of electrons ejected is proportional to:
A) their kinetic energy
B) their potential energy
C) the work function
D) the frequency of the incident light
E) the number of photons that hit the sample
Q:
The units of the Planck constant hare those of:
A) energy
B) power
C) momentum
D) angular momentum
E) frequency
Q:
Two isotopes of hydrogen fuse to form a helium nucleus and a neutron:2H + 3H -> 4He + nThe masses are: 2H:2.013553 u3H:3.015501 u4He:4.001506 un:1.008665 uWhat is the Qvalue of this reaction?A) 1.9 MeVB) 2.5 MeVC) 2.8 MeVD) 17.6 MeVE) 938 MeV
Q:
A particle with rest mass m moves with speed 0.6c. Its kinetic energy is:
A) 0.18mc2
B) 0.22mc2
C) 0.25mc2
D) mc2
E) 1.25mc2
Q:
A particle with zero mass and energy Ecarries momentum:
A) Ec
B) Ec2
C) D) E/c
E) E/c2
Q:
According to the theory of relativity:
A) mass is a form of energy
B) moving particles lose mass
C) momentum is not conserved in high speed collisions
D) a rod moving rapidly sideways (perpendicular to its length) is shorter along its length
E) a rod moving rapidly sideways (perpendicular to its length) is longer along its length
Q:
Two electrons move in opposite directions at 0.70cas measured in the laboratory. The speed of one electron as measured from the other is:
A) 0.35c
B) 0.70c
C) 0.94c
D) 1.00c
E) 1.40c
Q:
An event occurs at x= 500 m, t= 0.90 in one frame of reference. Another frame is moving at 0.90cin the positive xdirection. The origins coincide at t= 0 and clocks in the second frame are zeroed when the origins coincide. The coordinate and time of the event in the second frame is:
Q:
Two events occur on the xaxis separated in time by tand in space by x. A reference frame, traveling at less than the speed of light, in which the two events occur at the same coordinate:
Q:
A meter stick moves sideways (that is, in a direction perpendicular to its length) at 0.95c. According to measurements taken in the laboratory, its length is:
A) 0 m
B) 0.098 m
C) 0.31 m
D) 1.0 m
E) 3.2 m
Q:
Pi mesons at rest have a half-life of T.If a beam of pi mesons is traveling at a speed of, the distance in which the intensity of the beam is halved is:
Q:
A train traveling very fast (v= 0.6c) has an engineer (E) at the front, a guard (G) at the rear and an observer (S') exactly half way between them. Both E and G are equipped with yellow signaling lamps. The train passes a station, closely observed by the station master (S). Both E and G use their lamps to send signals. According to both S and S' these signals arrive simultaneously at the instant S' is passing S. According to S':
A) E and G sent their signals simultaneously from different distances
B) G sent his signal before E and from further away
C) G sent his signal before E but was the same distance away
D) E sent his signal before G and from further away
E) none of the above
Q:
Figure (i) shows a double-slit pattern obtained using monochromatic light. Consider the following five possible changes in conditions:
1) decrease the frequency
2) increase the frequency
3) increase the width of each slit
4) increase the separation between the slits
5) decrease the separation between the slits
Which of the above would change Figure (i) into Figure (ii)? A) 3 only
B) 5 only
C) 1 and 3 only
D) 1 and 5 only
E) 2 and 4 only
Q:
The resolving power of a telescope can be increased by:
A) increasing the objective focal length and decreasing the eyepiece focal length
B) increasing the lens diameters
C) decreasing the lens diameters
D) inserting a correction lens between objective and eyepiece
E) none of the above
Q:
Light of wavelength 480 nm falls on a slit of width 3.5 m. What is the relative intensity (that is, the value of I/Im) of the diffraction pattern at an angle of 18?
A) 2.4 x 10-4
B) 1.7 x 10-3
C) 1.1 x 10-2
D) 1.0 x 10-1
E) 1.0
Q:
A plane wave with a wavelength of 500 nm is incident normally on a single slit with a width of 5.0 x10-6m. Consider waves that reach a point on a far-away screen such that rays from the slit make an angle of 1.0ï‚°with the normal. The difference in phase for waves from the top and bottom of the slit is:A) 0 radB) 0.55 radC) 1.1 radD) 1.6 radE) 2.2 rad