UK mains electricity & current reversals

[woollymac]

The frequency of UK mains electricity is 50Hz. I know that this means there are 50 cycles per second & so it must change direction 50 times per second but a colleague is adament that this means the current reverses direction 100 times per second. I just can't get it. Can anyone explain this to me?

 

[MATLABdude]

The current flows one way through the first half of the sinusoid, and then flows the other way during the other half. These together form one cycle:
http://en.wikipedia.org/wiki/Sine_wave

 

[woollymac]

Thanks - easy when you say it like that.