IB HL Physics Misunderstood Concepts 2

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Below are some HL questions on concepts that are not well understood.

  1. A metallic surface is irradiated with infrared radiation and photoelectrons are emitted from the surface. This radiation is replaced by ultraviolet light of the same intensity. How does this affect the kinetic energy of the emitted photoelectrons and their rate of release?
  2. A mass m is tied to a string and revolves in a circular path of radius R in a vertical plane. What is the least total energy of the mass if it is to maintain its circular motion?
  3. A train has a whistle of frequency f. The train moves to the east at a constant speed v. Another train also has a whistle of the same frequency and this train moves to the west at a constant speed v. What is the frequency of the sound heard on the train moving to the west?
  4. The diameter of a nuclide of mass number 2A is 3r. What is the radius of a nuclide of mass number 3A?
  5. A mass m has a total energy E when it moves in simple harmonic motion of amplitude A on a spring. What is the total energy of the motion if a mass m is added and the amplitude is increased by 50%?
  6. A wind farm consisting of 65 turbines, each of power 15 MW, would generate the same amount of energy as a typical nuclear plant of 975 MW. True or false? (reference, Physics World, March 2011)
  7. Which is closest to the efficiency of commercial solar panels made of silicon that are used on rooftops, 20%, 50%, 75%, 100%? (reference, Physics World, April 2021)