2018 H2 Chem P1 Q1 — Atomic structure Solution

The answer is D.
Protons are positive, so they bend towards the negative plate. Electrons are negative, so they bend towards the positive plate.
The angle of deflection is proportional to charge/mass. Both particles carry a charge of the same size, \(1.60 \times 10^{-19}\text{ C}\), but an electron is much lighter:
\(\left|\dfrac{q}{m}\right|_{e} = \dfrac{1.60 \times 10^{-19}}{9.11 \times 10^{-31}} = 1.76 \times 10^{11}\text{ C kg}^{-1}\)
\(\left|\dfrac{q}{m}\right|_{p} = \dfrac{1.60 \times 10^{-19}}{1.67 \times 10^{-27}} = 9.58 \times 10^{7}\text{ C kg}^{-1}\)
So the electrons are deflected about 1840 times more strongly than the protons: a sharp bend towards the positive plate for electrons and only a slight bend towards the negative plate for protons. This is diagram D.
• A is wrong: both directions are reversed (protons are drawn going to the positive plate and electrons to the negative plate), and the two beams are drawn with equal deflections.
• B is wrong: the directions are right, but the protons and electrons are drawn with equal deflections, although the electron has a far larger charge/mass ratio.
• C is wrong: the directions are reversed; protons are drawn bending towards the positive plate and electrons towards the negative plate.