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Brainstorm of Possible Questions/Topics for A2 Data Handling and Experimentation

  1. Nov 17, 2009 #1
    Hi

    I am soon (well... in 8 weeks) sitting my OCR A2 level (Advancing physics) examination.
    The exam is based mainly on experimentation and data handling techniques.
    Anyway, I have been given an official "pre-release reading" with loads of information in it. What I need to do now is brainstorm of what kind of questions or topics could be asked.

    The Pre-Release is as follows: (I have formatted the text bold etc. in the same way that OCR has but have had to describe images)

    1. Calibration of Instruments

    Sensor circuits usually need calibration before they can be used to make measurements. This involves measuring the output for different values of the input variable. Measurements using the thermistor circuit shown in figure 1 (figure 1 shows an image of a Thermistor and Resistor connected in series to a 6V Cell with a Voltmeter around the Resistor) give the graphs shown in figure 2 (Figure 2 shows a graph of Output P.d./V (y axis) against Temp/degrees C (x axis) with three lines. One showing a 50000ohm fixed resistor from 2.8V on the y axis. The line below shows a 5000ohm resistor from 0.4V and the bottom line shows a 500ohm resistor from just above 0V. The top line has a slightly downward curve to 5.95V. The middle line is linear to 4.7V and the bottom line has an upward curve to 1.6V (x axis from 0 to 100 degrees and y axis from 0 to 6 Volts).

    These three calibration graphs show that using different values of a fixed resistor changes the sensitivity of the circuit at different points of the temperature range, and also affects the linearity of the relationship between input and output. The range of output values obtained is different in each case which affects the resolution of the circuit.

    2. Spectacles for the Third World

    Some Charities collect old spectacle lenses for reuse in the Third World. The power of these lenses ranges from +5D (converging) to -5D (diverging) with the majority being in the latter category. The power of each lens needs to be measure quickly and easily when it arrives at its destination using appropriate technology and expertise.

    Measurement of the power of a lens is easy. All you need is a single beam of parallel light, some white card and a ruler. You can measure the focal length and then find the power of a lens.

    However, this method does not work for diverging lenses because the light which leaves the lens appears to come from a point behind it. The wave fronts therefore diverge after going through the lens and never meet at a focus.

    The way that the power of a diverging lens can be measured is to focus light to a point on a screen using a converging lens to arrange for the incoming light beam to be already aiming at a focus.

    A charity appoints an engineer to design a simple method for use in the Third World to measure the power of diverging spectacle lenses. The equipment the engineer must use comprises of: a light source, a converging and/or diverging lens, a ruler and a cardboard screen.

    The procedure she uses is:

    1. With both lenses used, measure the distance from the diverging lens to the position on the screen where light comes to a focus. Call this distance 'v'.
    2. Remove the diverging lens and move the screen manually until the light is focussed by just the converging lens. Call this distance 'u'.
    3. Calculate the power P of each spectacle lens using the formula P=(1/v)-(1/u) where both the image distance 'v' and the object distance 'u' are positive because they are to the right of the lens

    Here is a table of measurements obtained by the above procedure. Different pairs of values u and v are obtained by changing the distance from the light source to the converging lens.
    u/cm 10 11 12 13 14 15
    v/cm 17 21 24 29 36 42

    3. Performance of commercial Jet Aircraft

    Although much criticised for their carbon footprint, modern jet aircraft have been developed to carry a very large load at a great speed, using the least fuel possible. This makes good economic sense. However, some of these factors compete with each other: The fastest commercial jet aircraft Concorde was stopped in 2003 for economic reasons as it could not carry enough passengers to make its journey's profitable.
    Weight and Range
    More recent Jet Aircraft are designed to carry more passengers and load than Concorde. They need to travel one quarter of the way around the earth without refuelling. This means they need to carry a lot of fuel which is heavy, sometimes up to one third of the total weight of the Plane. The Planes themselves are also necessarily larger which further increases the weight to be carried.
    Lift
    In level flight, lift is produced by pressure differences caused by airflow across the wings. The magnitude of lift depends on the wing size and the surface area of the wing. Cruising Speed of jet aircraft are commonly similar, being just less than the speed of sound. This means that the factor which most affects lift is the shape and surface area of the wings.
    Take-off
    Aircraft use fuel very rapidly at take-off, when the engines have to deliver maximum thrust. The aircraft must accelerate fast enough to reach the speed needed for take-off usually 240-290 Km h^-1 (150-180mph). This has to be achieved within the length of the runway. Because take-off speeds and runway lengths are all rather similar, the acceleration of most jet aircraft down the runway is similar, whatever their mass and total engine thrust.

    After take-off, jet aircraft are required to climb steeply to avoid excess noise nuisance. If the angles of climb are similar, this also requires maximum thrust to be related to total aircraft take-off weight.

    Data on six aircraft are given in the table:

    Type no.of engines max.engine thrust max.takeoff mass/kg takeoff distance/m
    Airbus A340 4 152 284000 3400
    Airbus A340b 4 276 365000 3200
    Boeing 777 2 343 247000 3100
    Boeing 747 4 264 397000 3600
    DC10-40 3 236 251700 2800
    MD-11 3 270 273900 3100


    Type cruising speed km/h fuel economy litres/hour fuel capacity/litres
    Airbus A340 876 8000 155400
    Airbus A340b 902 9800 195600
    Boeing 777 900 7700 117300
    Boeing 747 925 14,160 216800
    DC10-40 965 10,800 138700
    MD-11 945 9000 146000


    Type range/km wing surface area/m^2
    Airbus A340 13500 362
    Airbus A340b 13900 437
    Boeing 777 9000 430
    Boeing 747 13500 525
    DC10-40 9300 339
    MD-11 12600 339
     
  2. jcsd
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