iGCSE Physics (0625) 5.1.1 The atom Paper 4 -Exam Style Questions- New Syllabus

Correct Answer: (i) Most of the atom is empty space. (ii) The nucleus is positively charged / concentrated mass.

Detailed solution: (i) Since the majority of α particles pass through without any deflection, it implies they do not encounter any obstacles, concluding that the atom is mostly empty space. (ii) Large-angle deflections occur when the positive α particles come close to a concentrated positive center. This confirms the existence of a small, dense, positively charged nucleus containing most of the atom’s mass.

Correct Answer: (i) Path P. (ii) Direction: Upwards.

Detailed solution: (i) Path P represents alpha particles because they are much more massive than beta particles (Path R), resulting in a smaller deflection for the same field strength. (ii) The electric field is directed upwards from the positive plate to the negative plate. Alpha particles are positively charged and thus experience a force in the direction of the field, causing them to curve toward the top (negative) plate.

Correct Answer: $1.9 \times 10^{-2}\text{ g}$

Detailed solution: First, determine the number of half-lives: $n = \frac{480}{160} = 3$ half-lives. To find the initial mass, we multiply the final mass by $2^n$, which is $2^3 = 8$. Calculating the initial mass: $M_0 = 2.4 \times 10^{-3}\text{ g} \times 8 = 19.2 \times 10^{-3}\text{ g}$. This is expressed in standard form as $1.92 \times 10^{-2}\text{ g}$, rounded to $1.9 \times 10^{-2}\text{ g}$ for two significant figures.