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# Physics def

Question | Answer |
---|---|

What is an electric current? | The net flow of charged particles |

Define the Coulomb | The amount of charge that flows in 1 second when the current is 1 Amp |

State Kirchhoff’s first law | The sum of the currents entering a junction is equal to the sum of the current leaving that junction. Conservation of charge |

Define Potential Difference | The energy transferred per unit charge from electrical into other forms |

Define Electromotive Force | The energy transferred per unit charge to electrical from other forms |

Define the Volt | The potential difference required to carry 1 Amp of current against 1Ω of resistance |

Define resistance | Resistance opposes the current. It is the potential difference per unit current |

Define the Ohm | The resistance between two points with a potential difference of 1V which has a current of 1A |

State Ohm’s Law | The current flowing through a metal is directly proportional to the potential difference across it providing the temperature remains constant |

Define resistivity, ρ | ρ = RA/l where R is the resistance of the sample wire, A is the cross-sectional area and l is the length of the wire |

Define power | The rate of energy transfer |

Define a kilowatt-hour | A unit of energy. The energy used by a 1kW device in 1 hour |

State Kirchhoff’s Second Law | The sum of the e.m.fs = sum of p.d. around a closed loop of a circuit. Conservation of energy |

What is the terminal p.d.? | The terminal p.d. of a source of emf is the potential difference across its terminals |

Define displacement | How far and in what direction the point/particle is from its equilibrium position |

Define amplitude | Maximum displacement of a point/ particle caused by a wave motion |

Define the period of a wave | The periodic time is the time taken to make one complete oscillation/ rotation |

Define wavelength | The distance between two consecutive points on a wave that are in phase |

Define frequency | The number of wavelengths/ oscillations passing a point per unit time |

Define speed of a wave | The distance travelled by the wave (energy) per unit time |

What is the Principle of Superposition? | Where waves cross the total displacement is the vector sum of the individual displacements due to each wave at that point |

Explain what the term interference means | In a region where wave trains from coherent sources cross/meet, superposition occurs. The pattern is formed from the vector sum of the individual displacements |

Explain what constructive interference is | A region where wave trains from coherent sources meet, superposition occurs giving complete reinforcement of the waves, through the vector addition of the displacement of the individual waves |

Explain what destructive interference is | A region where wave trains from coherent sources meet, superposition occurs giving complete cancellation of the waves, through the vector addition of the displacements of the individual waves |

What is coherence? | If sources of wave are coherent there must be a constant phase difference between them and therefore they must have the same frequency. They must have also approximately the same amplitude |

Define path difference | Difference in length/distance to travel between detector and each wave source (measured in metres/centimetres etc.) |

Explain what is meant by phase difference | The phase difference between two points on the same wave (or waves of the same frequency) is how far through the cycle one point is compared to the other, measured in degrees or radians |

Explain what a node is | On a standing wave, a node occurs where the amplitude/displacement is (always) zero |

Explain what an antinode is | Antinodes occur where the amplitude (of the standing wave) takes the maximum (possible) value |

Define the fundamental mode of vibration | Mode of vibration with the lowest possible natural frequency |

Define a harmonic | The frequencies at which a standing wave is produced in the given situation (it would have a set number of wavelengths given the situation) |

What is a photon? | A quantum (set amount) of energy of EM radiation |

Define an electronvolt | A unit of energy, it is the energy transferred to an electron when it is accelerated through a potential of 1V |

Define the work function | Minimum amount of energy needed to release an electron from the surface of a metal, symbol: Ф |

Define threshold frequency | Minimum frequency that will cause photoemission from a material, hf=Ф |

Define mean drift velocity | The average displacement of charge carriers along the wire per unit time |