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Flashcards by Eleanor Ryan, updated more than 1 year ago
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| Question | Answer |
| What is the shortest stopping time for a car which is travelling at \[16m s^{-1}\] and has a maximum deceleration of \[2.5 m s^{-2}\] ? | \[v = u + at\] / \[s = ut + \frac{1}{2}at^2\] / \[v^2 = u^2 +2as\] \[t = 6.4 s\] |
| State the law of conservation of momentum | momentum before = momentum after in a closed system / provided no external forces act |
| Explain why heat does not travel through solids by means of convection. | the particles cannot move (freely) |
| Storage heaters are frequently used to heat buildings. State the principle that underlies the operation of an electrical storage heater. | large heat capacity heated when electricity is inexpensive (off peak) / store a large quantity of energy / release energy slowly (during the day) |
| If a diamond has a refractive index of 2.42, what is the speed of light in the diamond? | \[n = \frac{c_1}{c_2}\] \[c_2 = \frac{3*10^8}{2.42} = 1.24 * 10^8 m s^{-1}\] |
| Define the volt. | potential difference (between two points) if 1 J (of work) is needed to move 1 C (from one point to the other) |
| A positively charged rod is brought near to a neutral, conducting sphere that is on top of an insulating stand. How would a student charge the sphere negatively by induction? | earth the sphere (stated or implied) 4 remove earth (connection) and then remove rod |
| Explain what is meant by the statement: “Zinc has a threshold frequency of \[1.04 × 10^{15}\] Hz”. | below this frequency e.m.r. /photons will not cause emission of electrons (from zinc surface) |
| Give one benefit of switching from fossil fuels to nuclear power for the generation of electricity. Explain your answer | more energy per kg / less carbon dioxide produced / production of useful radioisotopes etc. explanation |
| Give an expression for the minimum frequency of a photon that can form an electron and a positron by pair production. | \[(f=) \frac{2m_e c^2}{h}\] |
| What event inside an LED causes the release of a photon? | electron combines with (positive) hole |
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