In a photoelectric-effect experiment, the stopping potential was measured for several different wavelengths of incident light. The data are as follows:

Wavelength (nm)..................Stopping potential (V)
500....................................................0.19
450....................................................0.48
400....................................................0.83
350....................................................1.28
300....................................................1.89
250....................................................2.74

Use an appropriate graph of the data to determine 

(a) The metal used for the cathode 

(b) An experimental value for Planck’s constant.