FFT of sine wave not coming as expected i.e single point

The cyan plot is a spectrum of 50 Hz, and the magenta one is a 50.1 Hz sine wave (having amplitude 0.7). Both are sampled at 1024 samples/s. I performed a 1024 point FFT to get this spectrum.

Why is only the 50Hz spectrum a single value? Why does the 50.1 Hz sine consist of other frequencies apart from 50.1 Hz; where do these new frequencies come from?

I did not do any non-linear processing on the 50.1 Hz signal! Also the 50.1 Hz appears to have smaller maximum amplitude, i.e. it's not 0.7, when in fact the sine wave I generated has an amplitude of 0.7.

Why is this?

Obtained by MATALB command fft();