VERY early Doctor Who. This scene they were focusing on doing science as accurately as possible, back when it was still going to be mostly an educational show. Early in the 5th Doctor they did the same, with good science advisors on board. As Doctor 5 was my “main” initial Doctor, it inspired me to also be fascinated by science, although it’s a chicken-egg as to which came first – my interest and the show reflecting that – or the show inspiring me.
Also love the double thumb-biting at the end. I always thought that was a hallmark of the 4th Doctor but it looks now like he drew it from the 1st.