IBDP Physics- E.1 Structure of the atom- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Robert Millikan’s oil-drop experiment (1909) first provided direct evidence that electric charge is quantized in discrete units of the elementary charge e.
✅ Answer: (B) Millikan
▶️ Answer / Explanation
The radius of a nucleus is given by \( R = R_0 A^{1/3} \), where \(A\) is the mass number.
Hence the volume of a nucleus is proportional to \( R^3 \propto A \).
The mass of a nucleus is also proportional to \(A\). Therefore,
\[ \text{density} = \frac{\text{mass}}{\text{volume}} \propto \frac{A}{A} = \text{constant} \]
This shows that nuclear density is approximately the same for all nuclei.
✅ Answer: D
▶️ Answer / Explanation
In the Bohr model for hydrogen:
\( r_n \propto n^2 \) and \( v_n \propto \dfrac{1}{n} \).
The question states that \( r_{2} = 4 r_{1} \), which is consistent with \( r_n \propto n^2 \).
Since \( v_n \propto \dfrac{1}{n} \), the ratio of speeds is
\[ \frac{v_{2}}{v_{1}} = \frac{1/2}{1/1} = \frac{1}{2}. \]
✅ Answer: (B)