paper 1

• Direct potential difference


  the polarity (of the supply) does not change
• Explain why taking the measurements more than once may improve accuracy.

  a mean can be calculated, which reduces the affect of random error
• Exam question: Why might a regular thermometer be more difficult to read than a digital one?

  Viewing angle affects measurement, parallax error,
• What is internal energy?

  Internal energy - the sum of all the kinetic energy and potential energy of all particles in a substance, only one can change at a time.
• Exam question: A negatively charged rod is held near an earthed conductor. Explain why a spark jumps between the negatively charged rod and the earthed conductor.


  the (large) potential difference between the two objects (causes negative) electrons / charges to move (through the air) (from the rod) to the conductor
• Exam question: Explain why a step-up transformer is used in the national grid (4)

  step-up transformer increases potential difference. and decreases current, reducing (thermal) energy transfer to surroundings or reducing (thermal) energy transfer from transmission cables, increasing the efficiency (of power transmission)
• What is meant by a zero error?

  Ammeter displays a reading when not connected
• Exam question: The negatively charged student touches a metal tap and receives an electric shock. Explain why.

  there is a potential difference between the student and the tap which causes electrons to transfer from the student which earths the charge
• Exam question: some carpets have thin copper wires running through them. The student is less likely to receive an electric shock after walking on this type of carpet. Suggest why.

  carpet/copper has a low resistance lower build-up of charge (on the student) or (so there is a) smaller / no potential difference between student and tap/earth
• Exam question. How does cycling uphill affect the maximum speed of a cyclist? Explain.

  maximum speed is lower because the maximum power output of the cyclist is constant but additional work is done against gravity
• Exam question: Explain how the resistance of a filament lamp changes as the potential difference across it increases. 


  the current increases when the potential difference increases which causes the temperature of the filament to increase so the resistance increases
• Exam question: What does more energy efficient mean?

  a higher proportion of the total energy input is usefully transferred (BTW. wastes less energy is insufficient)
• Exam question: Explain why the radiation source inside the smoke alarm should have a long half-life. 


  (a long half-life means) the count rate is (approximately) constant if it decreases too low it will trigger the alarm (so don’t have to replace source or smoke detector is insufficient)
• Exam question: The internal energy of the air increases as the tyre is inflated. Explain why.

  work is done on the air (in the tyre) so the temperature (of the air) increases
• fuels used in nuclear power stations:

  Uranium and plutonium
• Exam question: describe the process of nuclear fission.

  a neutron is absorbed by a (large) nucleus the nucleus splits into two (smaller) nuclei releasing energy (and gamma rays) and (two / three) neutrons