Measure Light Speed and Refractive Index 1.Experimental Methods Considering a periodical light signal, 1=1+Alo cos(2πvt) (1) where v is the frequency.Shining the light on a photodiode,after filter out the DC component,the photodiode's voltage can be written as, U=Un cos(27vt) (2) If the light signal travel additionalin air(vacuum),the comresponding time is,and the phase differeciThe signal of the photodiodes U=U,cos(2πvt-△0) (3) Once and s are measured,the light speed can be obtained by △s C= At (4) The frequency of visible light is in order of1Even frequency of modulated light isas high as10 It's hard to observe these high frequency signals directly with a normal oscilloscope.However,one can "overlap"the signal with another signal with frequency which is very close to the original The new signal is, U1=U'cos(2πvt-△g)cos2rVt 1 =5U'(cos[2πv+v't-△]+cos[2πv-v')t-△g]0 (5) Aferfteringout the high frequeney compoents,thecan be transformtobe.Measure Light Speed and Refractive Index 1. Experimental Methods Considering a periodical light signal, , (1) where v is the frequency. Shining the light on a photodiode, after filter out the DC component, the photodiode’s voltage can be written as, (2) If the light signal travel additional in air (vacuum), the corresponding time is ，and the phase difference is . The signal of the photodiode is, (3) Once and are measured, the light speed can be obtained by (4) The frequency of visible light is in order of . Even frequency of modulated light is as high as . It’s hard to observe these high frequency signals directly with a normal oscilloscope. However, one can “overlap” the signal with another signal with frequency , which is very close to the original . The new signal is, (5) After filtering out the high frequency components, the can be transform to be