2020年10月IB物理(SL)真题PDF下载-paper3
1. A spherical soap bubble is made of a thin film of soapy water. The bubble has an internal air pressure Pi and is formed in air of constant pressure Po. The theoretical prediction for the variation of (Pi - Po) is given by the equation
Pi - Po =4g/R
where γ is a constant for the thin film and R is the radius of the bubble.
Data for (Pi - Po) and R were collected under controlled conditions and plotted as a graph showing the variation of (Pi - Po) with 1/R.
(a) Suggest whether the data are consistent with the theoretical prediction.
(b) (i) Show that the value of γ is about 0.03.
(ii) Identify the fundamental units of γ .
(iii) In order to find the uncertainty for γ , a maximum gradient line would be drawn.On the graph, sketch the maximum gradient line for the data.
(iv) The percentage uncertainty for γ is 15 %. State γ , with its absolute uncertainty.
(v) The expected value of γ is 0.027. Comment on your result.
2. A student studies the relationship between the centripetal force applied to an object undergoing circular motion and its period T.
The object (mass m) is attached by a light inextensible string, through a tube, to a weight W which hangs vertically. The string is free to move through the tube. A student swings the mass in a horizontal, circular path, adjusting the period T of the motion until the radius r is constant. The radius of the circle and the mass of the object are measured and remain constant for the entire experiment.
The student collects the measurements of T fi ve times, for weight W. The weight is then doubled (2W) and the data collection repeated. Then it is repeated with 3W and 4W. The results are expected to support the relationship
W=4π2mr/T2
(a) State why the experiment is repeated with different values of W.
In reality, there is friction in the system, so in this case W is less than the total centripetal force in the system. A suitable graph is plotted to determine the value of mr experimentally. The value of mr was also calculated directly from the measured values of m and r.
(b) Predict from the equation whether the value of mr found experimentally will be larger,the same or smaller than the value of mr calculated directly.
(c) (i) The measurements of T were collected five times. Explain how repeated measurements of T reduced the random error in the final experimental value of mr.
(ii) Outline why repeated measurements of T would not reduce any systematic error in T.
2020年10月IB物理(SL)真题余下省略！
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