type: fill_blank | subtopic: Active Recall

1. In Rutherford's experiment, the particle that was fired at the gold foil was the __________ (alpha particle).

2. The distance of closest approach is d = __________. (2k$Ze^{2}$/KE)

3. Bohr's second postulate: angular momentum L = __________ where n is the principal quantum number. (nℏ = nh/2π)

4. The orbital radius in the Bohr model is r_n = __________ × $n^{2}$/Z Å. (0.529)

5. The total energy of the electron in the nth orbit is E_n = __________ eV (for Z=1). (−13.6/$n^{2}$)

6. KE = __________ and PE = __________ in terms of total energy E. (−E and 2E)

7. The hydrogen spectral series in the visible region is called the __________ series. (Balmer)

8. The number of spectral lines from the nth level is N = __________. (n(n−1)/2)

9. The Rydberg constant R = __________ $m^{-1}$. ($1.097 \times 10^{7}$)

10. The nuclear radius formula is R = $R_{0}$ × __________, where $R_{0}$ = 1.2 fm. (A^(1/3))

11. Nuclear density is __________ for all nuclei. (constant / approximately $2.3 \times 10^{17}$ kg/$m^{3}$)

12. Binding energy is calculated from mass defect as BE = $\Delta m$ × __________ MeV. (931.5)

13. The most stable nucleus (highest BE/A) is __________. (Fe-56)

14. The radioactive decay law is N = $N_{0}$ × __________. (e^(−λt))

15. Half-life t_{1}/_{2} = __________ / λ. (0.693)

16. Mean life τ = __________ × t_{1}/_{2}. (1.443)

17. After 4 half-lives, the fraction remaining is __________. (1/16)

18. In alpha decay, A decreases by __________ and Z decreases by __________. (4 and 2)

19. In beta-minus decay, A __________ and Z __________. (unchanged, increases by 1)

20. The SI unit of radioactive activity is __________. (becquerel, Bq)