4.4.5 Data recording and processing
Record observations in Table 4.4.1.
Table 4.4.1 Volt-Ampere characteristic experiment data record table
1)Draw the volt-ampere characteristic curve and determine the cut-off voltage
Use voltage as the X axis and current as the Y axis to draw the volt-ampere characteristic curve.Note that the voltage division value and current division value selection should be more appropriate,and try to make the length and width coordinated.Use thin lines to draw a smooth curve.The experimental points should be roughly uniformly distributed on both sides of the curve(some points can fall on the curve).The sum of the distances from the points on both sides of the curve to the curve is close to the minimum,and the distance between both sides close to the same.
2)Find the cut-off potential of each photocurrent curve
According to the experimental principle:the cut-off voltage should be the intersection of the oblique straight part of the measured curve and the curved part.Therefore,the data point when the photocurrent starts to change should be selected as the starting point,and an oblique straight line should be drawn according to the requirements of drawing a straight line(or use the method of unary regression,and use this point as the starting point,select the data points with a larger range from the photocurrent at a certain interval of several or more than ten points,draw a straight line to fit an equation,and then use this equation to draw a straight line),then the point where the straight line meets the curve is the point corresponding to the cut-off voltage,and the corresponding voltage value here is the“inflection point”of the photocurrent curve,that is,the cut-off voltage at this frequency.After finding the cut-off voltage U0,fill in Table 4.4.2.
Table 4.4.2 Record table of incident light wavelength(frequency)and cut-off voltage
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3)Draw U0-ν relationship diagram based on the data in above
The X axis represents the frequency of light,and the Y axis represents the cut-off voltage.Then draw a straight line according to the aforementioned straight line or straight-line fitting method.It shows that the experimental results are the same as Einstein’s equation,which proves that Einstein’s equation is correct.
4)Calculate Planck constant h
(1)Get a straight line from the U0-ν relationship diagram,and solve the slope of the straight line;
(2)Solving the linear equation obtained by the least square method(straight line fitting method).
5)Calculate the work function of metal material
From Equation(4.4.3),we can get WS=hν-eU0(ν is any frequency of light;U0 is cut-off voltage at the frequency).
