Physics Modern Physics Level: High School
Radioactivity
44 g of petrified wood was found in a petrified forest . A sample showed a 14 C activity of 100 decays / minute . How long has the tree been dead (in years) ? (The half-time of carbon -14 is 5730 years and freshly cut wood contains 6.5 x 1010 atoms of 14 C per gram) .a) 32,300
b) 15,600
c) 8,500
d) 4,700
e) 2,400
Physics Modern Physics Level: High School
Radioactivity
The half-life of 131-I is 8.04 days . Three days after it was prepared , its activity was 0.5 microCi, How many curies (in microCi) were initially prepared ?a) 8.60
b) 3.70
c) 0.65
d) 0.055
e) 0.0039
Physics Modern Physics Level: High School
Photoelectric Effect
A magnesium surface has a work function of 3.78 eV . Electromagnetic waves with a wavelength of 215 nm strikes the surface and eject electrons . Find the maximum kinetic energy of the ejected electrons . Express your answer in electron volts .
Physics Modern Physics Level: High School
Photoelectric Effect
Ultraviolet light with a frequency of 2.50 1015 Hz strikes a metal surface and ejects electrons that have a maximum kinetic energy of 6.9 eV . What is the work function (in eV) of the metal ?
Physics Modern Physics Level: High School
Bohr’s Atomic Model
Using the concept of standing waves , de Brogile was able to derive Bohr’s stationary orbit postulate . He assumed that a confined electron could exist only in states where its de Broglie waves form standing-wave patterns . Consider a particle confined in a box of length L and fixed at both ends . Apply de Broglie’s concept to shows that the linear momentum of this particle is quantized with p = mv = nh/2L and the allowed states correspond to particle energies of En = n^2Eo, where Eo = h^2/(8mL^2)
Physics Modern Physics Level: High School
Which one of the following is demonstrated by the Compton Effect ?a) Time dilation
b) Length contraction
c) The uncertainty principle
d) Electrons have wave properties.
e) Electromagnetic radiation has particle properties
Physics Modern Physics Level: High School
Dual Nature
Which one of the following quantities is the same for all photons in vacuum ?a) Speed
b) Frequency
c) Kinetic energy
d) Wavelength
e) Total energy
Speed
It 3 x 10^8 m/s in vaccum for all photons .Physics Modern Physics Level: High School
Heisenberg’s Uncertainty Principle
An electron is located on a pinpoint having a diameter of 3 micro m . The mass of an electron is 9.10939 x 10” kg and the Planck’s constant is 6.62607 x 10 tilde 34 J*s . What is the minimum uncertainty in the speed of the electron ? Answer in units of m/s .
Physics Modern Physics Level: High School
Nuclear Fusion
One possible fusion reaction occurs when two deuterium nuclei combine to form nucleus of a helium atom. If the mass of each deuterium nucleus is 3.3444*10-27 kg and the mass of the helium nucleus is 6.6465*10-27 kg, how much energy is released when 1 kg of deuterium undergoes this fusion process ?
Physics Modern Physics Level: High School
Photoelectric Effect
The photoelectric effect is important for two reasons , firstly , it provides strong evidence for the particle nature of light , and secondly , it has a large number of practical applications .a) Give one experimental observation coming from the study of the photoelectric effect that provides strong support for the particle theory of light .
b) State two practical applications of the photoelectric effect .
c) The work function of sodium is 2.46 eV .
i) Find the maximum frequency of radiation needed to eject photoelectrons from a sodium surface .
ii) If the sodium , surface is illuminated with radiation of wavelength 3.00 x 10^-7 metres , calculate the maximum kinetic energy of ejected photoelectrons .
Physics Modern Physics Level: High School
Radioactivity
A radioactive element decays according to the equation N(t) = N0 e-^3 t , where N0 is the original number of atoms , and N(t) is the number of atoms remaining after a time t measured in days . If N0 = 2 x e 7, find the time after which 2 x e 5 atoms remain .
Physics Modern Physics Level: High School
Radioactivity
A radioactive element X decays to stable element Y . starting with a large pure sample of element X , after 5200 years the sample will be 81% element Y . the decay constant of element X is most nearly ( ) / yr .
Physics Modern Physics Level: High School
Bohr’s Atomic Model
Hydrogen emits a photon with wavelength lamda = 435 nm . Which transition between energy levels does this correspond to ?
Physics Modern Physics Level: High School
Bohr’s Atomic Model
What is the energy difference between an electron in n = 3 state and n = 5 state in hydrogen ? If the electron makes a transition from n = 5 to n = 3 this energy difference is carried away by a single photon . Calculate the wavelength expressed in nm , and the frequency of this emitted photon . In what part of the electromagnetic spectrum does it lie ?
Physics Modern Physics Level: High School
Photoelectric Effect
A Light of frequency 9.0 x 10^14 Hz incident on a metal surface is ejects photo-electrons having energy 1 eV . Calculate the work function W for this metal .