Ib Physics Hl Topic 13

1. Describe the photoelectric effect.

The photoelectric effect occurs at any frequency of light, but the intensity determines the number of electrons emitted.

The phenomenonwhere electrons are emitted from the surface of a metal after being exposed tolight of a particular frequency called the threshold frequency. Light below thethreshold frequency will not cause electrons to be emitted. Above the thresholdfrequency, the maximum KE of the electrons depends on the frequency of theincident light. The number of electrons emitted depends on the intensity oflight, and not the frequency. Emission of electrons is instantaneous, andconsiders that light can act as particles called photons.

The photoelectric effect involves the emission of protons from a metal surface when exposed to light.

The photoelectric effect is a result of chemical reactions between light and the metal surface.

The photoelectric effect involves the emission of electrons, not protons. It occurs only above the threshold frequency, and the number of electrons emitted depends on intensity, not frequency. The process is not due to chemical reactions.

Explanation

The photoelectric effect involves the emission of electrons, not protons. It occurs only above the threshold frequency, and the number of electrons emitted depends on intensity, not frequency. The process is not due to chemical reactions.

2. Explain how atomic spectra provide evidence for the quantization of energy in atoms.

B. The energy levels of electrons in atoms have no direct relation to the observed spectral lines.

C. Electrons in atoms can move between energy levels in a continuous manner without emitting light.

A. Atomic spectra show continuous changes in energy levels in atoms.

D. The concept of quantized energy states in atoms does not play a significant role in understanding atomic spectra.

An explanation in terms of energy differencesbetween allowed electron energy states issufficient. Max Planck suggested that electrons change their energy in quantizedamounts (E=hf). Spectral lines show that electrons shift orbits releasing orabsorbing discrete amounts of energy. Electrons occupy discrete energy levels.Movement between levels involves absorbing or emitting energy. When an electronmoves from a higher energy level to a lower energy level, it emits energy inthe form of light (photons).

The correct answer explains how energy differences between allowed electron energy states support the quantization of energy in atoms, while the incorrect answers provide misleading statements that do not accurately reflect the evidence provided by atomic spectra.

Explanation

The correct answer explains how energy differences between allowed electron energy states support the quantization of energy in atoms, while the incorrect answers provide misleading statements that do not accurately reflect the evidence provided by atomic spectra.

3. Explain how the radii of nuclei may be estimated from charged particle scattering experiments.

Oneexperiment that can be used is the Geiger Marsden experiment. An estimate ofthe radii of nuclei can come about through the principle of the conservation ofenergy. The KE of a particle approaching a nucleus is completely transformedinto electrostatic potential energy. At the distance of closest approach, theKE will be converted entirely to PE. The particle will be momentarily at rest.Use of energy conservation for determiningclosest-approach distances for Coulomb scatteringexperiments is sufficient.

Estimates can't be made from charged particle scattering experiments.

There is no relation between charged particle scattering experiments and estimating radii of nuclei.

Radii can be estimated only using theoretical calculations, not experiments.

4. Describe how the masses of nuclei may be determined using a Bainbridge mass spectrometer.

Studentsshould be able to draw a schematic diagram of the Bainbridge mass spectrometer,but the experimental details are not required.Studentsshould appreciate that nuclear mass values provide evidence for the existenceof isotopes.Positiveions of elements are pass through / accelerated through electric and magneticfields. Particles will pass into a detector. The mass of the nuclei can then bedetermined.eE = Bevor v = E/B

Nuclear masses are determined by analyzing the number of electrons surrounding the nucleus.

The masses of nuclei are determined by measuring the volume of the nuclei and calculating the density based on that volume.

Masses of nuclei are determined by heating them until they vaporize, then condensing the vapor and weighing the resulting solid.

The correct method for determining the masses of nuclei using a Bainbridge mass spectrometer involves passing positive ions of elements through electric and magnetic fields, and then detecting the particles to determine mass values. It does not involve methods like heating and condensing the nuclei, analyzing the number of electrons, or measuring volume to calculate density.

Explanation

The correct method for determining the masses of nuclei using a Bainbridge mass spectrometer involves passing positive ions of elements through electric and magnetic fields, and then detecting the particles to determine mass values. It does not involve methods like heating and condensing the nuclei, analyzing the number of electrons, or measuring volume to calculate density.

5. Describe one piece of evidence for the existence of nuclear energy levels.

Alpha particles and gamma rays have the same energy levels in all nuclei.

Nuclear energy levels can be continuously varied, with no specific values.

For example,alpha (?) particles produced by the decay of a nucleus have discrete energies;gamma-ray (?-ray) spectra are discrete.Studentsshould appreciate that the nucleus, like the atom, is a quantum system and, assuch, has discrete energy levels.When a nucleus decays by emitting an alpha particleor a gamma ray, the particles or photons emitted are only at specific energies(there is not a complete range of energies emitted, only certain specificlevels).An alpha particle or photon thus has an energy equalto the difference between energy levels of the nucleus.The gamma and alpha particle energies arecharacteristic of the emitting nucleus. The existence of nuclear energy levelsis proven.

Nuclear energy levels are not related to the decay of a nucleus but rather to external factors.

The correct answer highlights that alpha particles and gamma rays have discrete energies when emitted by a nucleus, indicating the existence of nuclear energy levels.

Explanation

The correct answer highlights that alpha particles and gamma rays have discrete energies when emitted by a nucleus, indicating the existence of nuclear energy levels.

6. Describe ?+ decay, including the existence of the neutrino.

Beta-plus decay involves the emission of a positron and a neutrino from the nucleus.

Students should know that ? energy spectra arecontinuous, and that the neutrino was postulatedto account for these spectra.

Alpha decay involves the emission of a helium nucleus from a heavy nucleus.

Gamma decay involves the emission of high-energy photons from an excited nucleus.

In this question, we are discussing ?+ decay and specifically the existence of neutrino to account for continuous energy spectra. The incorrect answers provided refer to different types of nuclear decay processes to create options for a multiple-choice question.

Explanation

In this question, we are discussing ?+ decay and specifically the existence of neutrino to account for continuous energy spectra. The incorrect answers provided refer to different types of nuclear decay processes to create options for a multiple-choice question.

7. State the radioactive decay law as an exponential function and define the decay constant.

Studentsshould know that the decay constant is defined as the probability of decay of anucleus per unit time.If the number of nuclei present in a sample at t = 0is N0, the number N still present at time t later is given byN = Noe-?twhere ? is the decay constant (the probability that anucleus will decay in unit time).

The exponential function in the decay law is N = Noe^(-kt).

The decay constant is the total number of radioactive nuclei in a sample.

The decay constant is the number of nuclei that decay per unit time.

The correct answer explains that the decay constant is the probability of decay of a nucleus per unit time and provides the correct formula for the radioactive decay law. The incorrect answers suggest misconceptions related to decay constant and the exponential function in the decay law.

Explanation

The correct answer explains that the decay constant is the probability of decay of a nucleus per unit time and provides the correct formula for the radioactive decay law. The incorrect answers suggest misconceptions related to decay constant and the exponential function in the decay law.