When the psychologist rejects the null hypothesis (so accepts experimental hypothesis)
give details about a type I error?
In reality there was not a significant relationship or difference between what was being investigated so they should have accepted the null hypothesis but did not
when could Type I errors happen?
When you run the statistical test using a siglevel that is toolenient eg p<0.1 or the 10%level
you're essentially allowing here for 10% of the time your results are actually due to chance but can still report that they are statisticallysignificant