Illustrating power using the example of flipping a coin 100 times and calculating the fraction of heads. The black and red dashed lines show, respectively, the distribution of outcomes assuming the probability of heads is 50% (null hypothesis) and 64% (specific value of the alternative hypothesis). Here, the power against this alternative is 80% (red shading).

https://netflixtechblog.com/interpreting-a-b-test-results-false-negatives-and-power-6943995cf3a8