2019 H2 Chem P1 Q2 — Atomic structure Solution

The answer is C (electrons towards the (+) plate, protons towards the (-) plate, electrons deflected more than protons).

• Direction: opposite charges attract. Electrons are negatively charged, so they bend towards the positive (+) plate. Protons are positively charged, so they bend towards the negative (-) plate.
• Amount: for particles entering at the same velocity, the angle of deflection is proportional to charge/mass. An electron and a proton carry the same size of charge (1 unit), but the electron's mass is only about \(\dfrac{1}{1840}\) of the proton's mass, so the electron has a much larger charge/mass ratio and is deflected much more.

• A is wrong: the relative amount is right, but both directions are reversed; a negative electron is repelled by the (-) plate, not attracted to it.
• B is wrong: both directions are reversed, and the proton, with the smaller charge/mass ratio, is deflected less, not more.
• D is wrong: the directions are right, but protons are about 1840 times heavier for the same size of charge, so they are deflected less than electrons.