Explain when a z-test would be appropriate over a t-test. 100 to 200 words

Researchers routinely choose an alpha level of 0.05 for testing their hypotheses. What are some experiments for which you might want a lower alpha level (e.g., 0.01)? What are some situations in which you might accept a higher level (e.g., 0.1)? 100 to 200 words