3.3.4 Experimental procedures
1)Adjustment of Young’s modulus apparatus
(1)Adjust the bottom screw of Young’s modulus apparatus so that the columns are vertical and the platform is in horizontal level.
(2)Clamp the upper part of the steel wire,and connect the bottom part of the wire to the weight holder through the wire clamp.
(3)Put two weights(1 kg each)on the weight holder to straighten the steel wire,and check whether the cylinder can slide freely in the hole of the platform.
(4)Put the front foot tips of the optical lever in the transverse groove of the platform while the rear foot tip is put on top of the cylinder.Make sure the three tips of the optical lever at the same horizontal plane.Attention:Don’t put the rear foot tip into the crack between the clamp and the platform.
2)Adjustment of optical lever and telescope
(1)Put the telescope at the front of Young’s modulus apparatus about 1-2 m away,and adjust the telescope to make it basically on the equal height with optical lever reflector.Then,make sure the plane mirror of the optical lever and the scale ruler in the telescope are parallel to the steel wire,as shown in Figure 3.3.1.
(2)Put the eye outside the telescope along the straight line formed by two foresights,and check the scale image in the reflector of optical lever.If the scale is not seen,adjust the telescope position or the angle of the plane mirror until the scale image is observed.
(3)Put the eye on the telescope and adjust the eyepiece to make the cross clear.Observe the scale image from the inside of telescope.If the scale image is not clear,you can adjust slightly the focal distance of the telescope until graduation line of scale ruler can be clearly seen.
(4)Record the scale reading ni with alignment to the cross.(https://www.daowen.com)
3)Measurement
(1)Load 1 kg weight to the weight holder one by one and record the scale readings ni each time from the telescope until the weights are completely loaded.Attention:do not swing the weight holder during the loading process.
(2)Unload the weights one by one,and record the scale reading n′i from the telescope at each step.Attentions:Under the same weights,the two scale readings(loaded and unloaded,ni and n′i should be basically similar.If there is a large difference between two scale readings under the same weights,it is necessary to find out the reason before continuing the experiment.
(3)Measure the values of L,D,d and b,respectively.L and D are measured by steel ruler.Three foot tips are stamped on paper to make an isosceles triangle and the vertical distance of connected line from rear foot tip to two front tips is optical lever constant b,which can be measured by the ruler.L,D and b are measured three times to reduce errors.Use a screw caliper to measure the diameter of the steel wire d at three equal spacing points(top,middle and bottom)and both two orthogonal directions at each point are considered.Then,the mean value is taken as the final result.
4)Tips and Attentions
(1)All the weights should be placed crosswise to avoid falling from Young’s modulus apparatus.
(2)It is necessary to record the scale reading until the weight holder is static.Otherwise,extra errors will be introduced.
(3)It is important to carefully adjust the ocular of the telescope to eliminate the disparity.
(4)The interval time of each loading(or unloading)should be kept the same as possible.It is necessary to avoid swinging the weight holder during the loading and unloading process.
(5)Don’t touch the optical surface of optical instruments with your hands.
