2 Physics Questions Feedback ASWatch this thread
I was doing the 2017 AQA As paper 1 Physics test and I would like some feedback on a couple of the longer questions (how much I would score), as my teacher won't reply to any emails since it is holidays . I am going into year 13, so is a score of high 50s / low 60s a good score if I am aiming for an A* next year?
As the potential difference across the lamp increases, the current through the lamp increases. This means more charge carriers are released and pass through the lamp each second, so the rate / number of collisions per second between delocalised electrons and positive metal ions in lattice increases. The ions vibrate more with a greater amplitude. This increases the temperature of the lamp and the resistance of the lamp increases, so the gradient of the graph decreases. This is because it becomes harder for a current to pass through the lamp .
In the discharge tube there must be a high pd to accelerate the electrons in the tube to the anode to a high speed. This ensures the electrons will have sufficient kinetic energy to cause excitation of hydrogen atoms ,as otherwise they wouldn't have enough kinetic energy to cause excitation and so would 'bounce off' hydrogen atoms in an elastic collision.
Electrons of sufficient energy will collide with hydrogen atoms, transferring their energy to hydrogen atoms. One electron will collide with one hydrogen atom only. To cause excitation, electrons must transfer energy exactly equal to the energy difference between the two energy levels (ground state and excited state). This means only electrons transferring certain amounts of energies can cause excitation. Once an electron has moved up from a lower to a high energy level, atom will de-excite and electrons will cascade down lower energy levels, emitting photons exactly equal in energy to difference between energy level transitions.
This provides evidence for figure 9 predicting spectrum in figure 8 because the lines in the spectrum will only form when photons are emitted of certain energies due to 9 transitions possible. Since photons have energy equal to hc/wavelength / hf, the lines will form at unique, certain wavelegths / frequencies.
For example, wavelength of 486nm corresponds to photon energy of 2.89ev, so -0.85eV - -3.40 eV energy transition, so a photon of this wavelength and energy will be emitted when an electron moves down from -0.85eV energy level to -3.40eV energy level.