A-level PHYSICS Paper 1

Section A Answer all questions in this section. Do not write outside the box Two stable isotopes of helium are 4He and 3He. 2 2 . An atom of 4He is produced in a rock that contains uranium. It is produced following 2 the radioactive decay of a 238U atom. The decay also creates an atom of 92 thorium (Th). Write an equation for the decay of 238U. 92 [2 marks] 238U → 92 . A 3He nucleus can be produced by the decay of a tritium nucleus 3H. 2 1 State and explain which exchange particle is responsible for this decay. [2 marks] Do not write outside the box . Before helium was identified, some scientists suggested that the lines of the helium spectrum seen in the absorption spectrum of the Sun were due to the presence of sodium and hydrogen. Discuss, with reference to the lines A to F in Figure 1, the evidence for and against this suggestion. [2 marks]