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Physics P6 Notes
Measuring Experiment
Suggest why it is more accurate, when using a ruler, to measure diameter for five marbles rather than measure the diameter of a single marble. effect of uncertainties reduced diameters of marbles vary Describe how the student uses the two blocks and the marble to determine a new accurate value for the diameter of a marble. Draw a diagram to show the arrangement. Describe clearly how the student ensures that the value for the diameter of a marble is as accurate as possible. use marble between two blocks and measure gap measure gap in at least two places and check equal to ensure blocks are parallel / rotate marble to different axis and take average of measurements
Pendulum Experiment
Explain why timing 10 oscillations gives a more accurate result for the period T than timing 1 oscillation (Timing) errors (due to reaction time) less significant / (same) error is spread over a longer time. reduces the effect of (reaction) timing errors / reduces the percentage error / uncertainty / the (reaction time) error is spread over 20 oscillations Suggest how the procedure can be improved to increase the accuracy of the result. (time a) greater number of oscillations
Describe one technique that you use to improve accuracy when measuring the time t for 10 oscillations. Use of fiducial point / counting from when pendulum passes the vertical / start counting from zero. Describe one technique that you use to improve accuracy when measuring the distance d. You may draw a diagram to help your description. Use of set square or similar horizontal aid OR metre rule close to bob / pendulum Explain how you would measure the distance d as accurately as possible. Draw a diagram to help your explanation. diagram to show (correct use of) a horizontal aid (e.g., a set-square / ruler), matching wording measure the diameter of the bob with two blocks and a ruler / micrometer, divide by 2 to find the radius and add this on to the length of the string measure to the top and the bottom of the bob, find the average
Another student suggests that T 2 is directly proportional to d. Explain briefly how to test
the suggestion using the results in Table 1.1.
plot a graph of T^2 against d (if directly proportional) it will be a straight line passing through the origin
Hooke’s Law Experiment
State what additional materials the student needs to continue the experiment More weights
Explain why method 2 would give a more accurate value for the density of the particles in this sample of sand. water displaces air (owtte) and (calculated) volume is actually that of particles / (idea of) gaps filled with water
Describe two possible sources of inaccuracy in the measurements taken in method 1 or method 2, even if they are carried out carefully.
sand surface not flat top pan balance only to nearest gram measuring cylinder graduations too large The student uses the top pan balance as shown in Fig. 1.3 to measure the mass of the five marbles. He measures the mass M0 of a beaker without the marbles and then measures the mass M5 of the same beaker containing the marbles. Describe one possible source of inaccuracy in the method described and suggest one improvement to reduce its effect. graduations on measuring cylinder too large use smaller measuring cylinder or greater number of marbles
Center of Mass Experiment
The accuracy of the result obtained by this procedure depends on the metre ruler, without a load, balancing with the pivot at the 50.0cm mark. A student finds that this does not happen. She adds a small piece of modelling clay to one end of the metre ruler to correct it. Suggest if this is a suitable change for this experiment. Explain your answer. No, as (mass of clay) increases / changes mass of metre ruler Or Yes, as (mass of clay) only a small % of mass of metre ruler / owtte Suggest one practical reason why it is difficult to obtain accurate readings for a and b. Difficult to obtain exact balance difficult to judge position of (centre of) load load / ruler may slide Describe the main difficulty that a student has when doing this experiment as accurately as possible. obtaining exact balance judging position of (centre of) load masses sliding on ruler Using only the apparatus provided for the experiment, explain briefly how you would determine the position of the centre of mass of the metre ruler. Balance rule on pivot, balance point is at centre of mass / Find where the rule balances / pivot point is read Describe a technique for ensuring that the ruler is as near as possible to being balanced. idea of allow to (just) tip one way then the other way / owtte
Cooling Experiment
for at least another 180 s / until the temperature is close to room temperature or stops decreasing State 2 control variables for this experiment. volume of water initial temperature material of beaker / thickness of beaker / surface area of beaker (same) lids room temperature / appropriate environmental factor Suggest one change to the experiment to reduce the water outside the beaker form cooling down. large(r) volume of water surrounding beaker A use of constant temperature water bath Suggest how to display the results to make it easier to see the trend in the rate of cooling. plot a graph of temperature against time OR cooling rate against time / temperature Suggest two changes to the experiment that the student makes to increase the rate of cooling of the hot water without changing the starting temperature of the hot water. Room temperature remains constant. remove lid thinner lid paint the beaker black stir the water change beaker to container that is a better conductor / named metal increase surface (area of water / beaker) use a wider beaker blow air over water surface / use a fan use a smaller volume of water State one precaution that you would take to obtain accurate temperature readings. Explain briefly the reason for this precaution. statement: view thermometer / scale / reading at right angles / eye level explanation: to avoid parallax error statement: stir (before taking reading) explanation: to distribute water evenly / to ensure that all the water is at the same temperature
statement: ensure thermometer does not touch the side / base of beaker explanation: temperature different to that of the bulk of the liquid statement: wait until the thermometer (reading) stops rising at the start explanation: so that the maximum temperature of the liquid is recorded Explain the reason for taking the reading at the bottom of the meniscus rather than at the top of the meniscus. negligible / very small volume / amount of water between the bottom and the top of the meniscus Suggest a change to the apparatus that produces a greater difference between the rates of cooling for lid A and lid B. Explain why the change produces a greater difference. insulate sides / stand on mat, thermal energy only escapes from surface use plastic beaker, less transfer of thermal energy by sides / bottom thicker lid, less conduction through lid use of fan, increases rate of evaporation use wider beaker, larger surface area (for evaporation to occur)
Lens Experiment
Describe a technique for obtaining an image that is as sharp as possible. move screen slowly / back and forth Describe two techniques that you use to obtain a clearly focused image. Move screen slowly / back and forth Darkened room / bright object In this type of experiment, it can be difficult to judge the screen position that produces the clearest image. Suggest two precautions or techniques to overcome this difficulty. darkened room / bright object move screen slowly / back and forth / approach clearest position from both directions (and average) Suggest one precaution that must be taken when setting up the apparatus to ensure accurate measurements. (lamp), object and lens at same height lens and screen perpendicular(to bench)
Ray Trace Experiment
Suggest a suitable distance apart for the pins for accurate ray tracing. pin separation should be as large as possible (5 cm min) Suggest techniques to use in this type of experiment to ensure results are accurate. thin lines / use sharp pencil look at base of pins / keep pins vertical thin pins State one precaution that you would take in order to produce an accurate ray trace. view bases of pins place pins (as) far apart (as possible) ensure pins are vertical sharp pencil / thin lines / thin pins Suggest one source of inaccuracy in this experiment, even if it is carried out very carefully. thickness of the light rays difficulty in aligning incident ray with FE difficulty of placing crosses accurately difficult to judge the centre of the ray Suggest one reason why different students, all doing this experiment carefully, may not obtain identical results. difficult to align pins / place pins accurately / pins (too) thick The measurement of a quantity is reproducible if a similar result is obtained when the measurement is repeated by a different method or under different conditions. Suggest how the student can adapt this experiment to check if the value of d/l is reproducible. repeat with [angle value] on the other side of the normal OR repeat with optical pins
Circuit Experiment
Explain one advantage of using a variable resistor for this purpose rather than the procedure carried out in (a) and (b). avoids connecting / disconnecting the circuit / can obtain a continuous set of values / easier (to change the current/resistance) / quicker / can obtain more values of resistance / current Name a single device that can be used to control the current in the circuit instead of adding extra resistors in series. variable resistor Suggest one advantage of using a variable resistor to change the current in the circuit. easy to obtain range of values can easily set current to chosen values Briefly explain one advantage of using a variable resistor to determine the resistance of resistor U rather than the procedure carried out in (b) and (c). can obtain continuous set of values more straightforward to change current can obtain more values easily Suggest one practical reason why other students might not obtain the same result as this student, even if they do the experiment carefully uncertain connection point on crocodile clip resistance wire irregular / curved / not uniform / differing thickness along wire Suggest one practical reason why students carrying out this experiment may not obtain the same readings as in Table 3.1. Assume that the procedure has been done carefully difficult to position crocodile clip accurately inconsistent connection with crocodile clip resistance wire not uniform Suggest one difficulty which explains why different students, doing the experiment carefully with the same equipment, may not obtain identical results difficult to judge position of crocodile clip difficult to measure wire to nearest mm contact between wire and crocodile clip not precise difficult to interpolate readings on meters between graduations The resistance wire can become very hot during this type of experiment. Suggest one change to the apparatus that prevents this reduce e.m.f. of power supply
