physics P7

• What did John Dalton think the atom was?

  A neutral solid sphere
• What did scientists deduce about the atom's structure?

  It has a small positively charged nucleus
• What orbits the nucleus of an atom?

  Negative electrons
• What model was developed after the discovery of electrons?

  The plum pudding model
• What is the plum pudding model of the atom?

  • A cloud of positive charge
  • Electrons embedded within it
• What were alpha particles fired at in the experiment?

  A thin sheet of gold foil
• What were the results of the alpha scattering experiment?

  • Most particles went straight through
  • Some were deflected slightly
  • 1 in 10,000 were deflected greatly
• How much smaller is the nucleus compared to the atom's radius?

  10,000 times smaller
• What particles make up the nucleus?

  • Positively charged protons
  • Neutrons (neutral charge)
• What is the overall charge of an atom?

  Uncharged overall
• Why does an atom have no overall charge?

  Equal numbers of protons and electrons
• What is the basic structure of an atom?

  Nucleus with protons and neutrons
• What is the nuclear model of the atom?

  • Nucleus at the center
  • Electrons orbiting around it
• What is the activity of a radioactive source measured in?

  Becquerel (Bq)
• What does 1 Bq represent?

  1 decay per second
• What do detectors like Geiger-Müller tubes measure?

  Count rate of decays per second
• What is radioactive decay?

  • Emission of nuclear radiation
  • Unstable nuclei become more stable
  • A random process
• What is ionisation in the context of radiation?

  Knocking electrons out of atoms
• What are the types of radiation?

  • Alpha
  • Beta
  • Gamma
• What happens to the nucleus during alpha decay?

  It loses two protons and two neutrons
• What is the ionising power of alpha radiation?

  Highest ionising power
• What is the range of alpha radiation in air?

  A few centimetres
• What stops alpha radiation?

  A sheet of paper
• What occurs during beta decay?

  A neutron changes into a proton and an electron
• What is the ionising power of beta radiation?

  High ionising power
• What is the range of beta radiation in air?

  Approximately 1 meter
• What stops beta radiation?

  A few millimeters of aluminum
• What is gamma radiation?

  Short-wavelength, high-frequency EM radiation
• What is the ionising power of gamma radiation?

  Low ionising power
• What is the range of gamma radiation in air?

  Virtually unlimited range
• What stops gamma radiation?

  Several centimeters of thick lead
• What is half-life in radioactive decay?

  • Time for half the unstable nuclei to decay
  • Time for the count rate to halve
• How can the half-life of a source be determined?

  From a graph of count rate against time
• How do you find the reduction in activity after half-lives?

  1. Calculate activity after each half-life
  2. Subtract final from original activity
• What is the mass number of an element?

  Number of protons plus neutrons
• What do all atoms of the same element have in common?

  Same number of protons in the nucleus
• What are isotopes?

  Atoms with the same protons but different neutrons
• What did Bohr suggest about electron orbits?

  Electrons orbit at specific energy levels
• What are the basic structures of an atom?

  • Nucleus containing protons and neutrons
  • Electrons orbiting in fixed energy levels
• What are the main conclusions from the alpha particle scattering experiment?

  • Most mass is concentrated in the nucleus
  • The nucleus is positively charged