t

N, the pendulum length is L=l+

d

2. From the periodic formula of simple pendulum T=2 π.

L

G de

g=

4 π 2 n 2 (l+

d

2 )

T2； The diameter of the ball d = 2.235 cm;

(2) a, only in the case of a small swing angle, simple harmonic vibration, so the angle of the pendulum from the equilibrium position can't be too big, generally not more than 5, so a is correct.

When the pendulum passes through the equilibrium position, it starts to time. On the one hand, it is convenient to measure the cycle; On the other hand, the speed of swinging the ball is the largest, resulting in a small time error. Therefore, B is correct.

C, let the ball swing in the same vertical plane as much as possible, and can't form a conical pendulum, otherwise the period will be reduced. So, C is correct.

D, the period of a simple pendulum has nothing to do with the quality of the pendulum ball, so D is wrong.

So choose ABC

(2)① The electromotive force of a dry battery E= 1.5V, and the resistance range of the sliding rheostat R 1 is 0? 10Ω, and the minimum current in the circuit is about I min =

E

R =

1.5

10 A=0. 15A, so the range of ammeter A is 3A, which shows that the range of ammeter A is too large.

(2) Set the modified ammeter range as I, with

I=I g +

I g R g

R 3 =0.003A+

3× 1 0 -3 × 100

0.5 A = 0.60 A.

③ In order to make the current in the circuit larger and easier to adjust, the sliding rheostat should be used in the experiment.

④ As can be seen from the above, the range of the modified ammeter is 200 times that of the ammeter G, and the longitudinal intercept B of the image is equal to the electromotive force of the power supply, and the electromotive force of the power supply read from the figure is E =1.48 V. 。

The slope of the graph line is k=r, which is known from mathematical knowledge.

1.48- 1.06

2.5×200× 1 0 -3 =0.84, and the internal resistance of power supply r = k = 0.84Ω.

So the answer is:

① Compared with the measured current value, the range is too large.

②0.60

③R 1

④ 1.48,0.84,3, (20 13? Dongcheng District (Mode 2) Experiment:

(1) In the experiment of measuring gravity acceleration with a simple pendulum:

① In the experiment, a classmate measured the diameter of the ball as D, the length of the cycloid as L, and recorded the total time for the ball to complete N complete vibrations with a stopwatch as T, then the expression of local gravity acceleration is G = _ _ _ _ (expressed by D, L, N, T). If students use vernier calipers to measure the diameter of the ball, as shown in figure 1, the diameter of the ball is.

(2) In order to minimize the experimental error, the following operation is feasible _ _ _ _.

The maximum swing angle of the cycloid relative to the vertical direction is less than 5.

B. Start timing when the ball passes the equilibrium position.

C let the ball swing in the same vertical plane as much as possible.

D. reduce the quality of the pendulum ball

(2) Some students want to measure the electromotive force and internal resistance of dry batteries.

① In addition to the switch S and wires, the laboratory also has the following equipment to choose from: voltmeter: V (range 3v, internal resistance RV =10Ω) ammeter: G (range 3mA, internal resistance Rg =100Ω) ammeter: A (range 3A, internal resistance about 0.5Ω) sliding rheostat: R/kloc- 10Ω, rated current 2A)R 2 (resistance range 0? 1 000Ω, rated current 1A) Constant resistance: R3 = 0.5ω Students drew the schematic diagram as shown in figure1according to the equipment, and the reason why ammeter A was not selected was _ _ _ _.

② The classmate connected the ammeter G in parallel with the constant resistance R 3, and actually modified the ammeter, so the corresponding range of the ammeter he modified is _ _ _ _ _ A. 。

(3) For accurate measurement and convenient operation, sliding rheostat _ _ _ _ _ _ (fill in the symbol of equipment) should be selected in the experiment.

(4) Using the data measured in the above experimental schematic diagram, students draw a graph as shown in Figure 2 with the reading of ammeter G as abscissa and voltmeter V as ordinate. According to the chart, the electromotive force of the power supply e = _ _ _ _ _ v (the result retains three significant figures) and the internal resistance r = _ _ _ _ _ _ω (the result retains two significant figures).