iGCSE Physics (0625) 4.2.1 Electric charge-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
When a negatively charged rod is brought near the metal sphere, it repels the free electrons within the conductor. These electrons move to the far side of the sphere. Since the far side is earthed, the repelled electrons flow away to the Earth, leaving the right side neutral. The near side (left) is left with a deficiency of electrons, resulting in a net positive charge ($+$) being induced there due to attraction to the negative rod. Consequently, the sphere retains only positive charges on the side closest to the rod, as shown in diagram D.
▶️ Answer/Explanation
Detailed solution:
Charging by friction occurs because of the transfer of electrons, which are the mobile negative charges in solids.
When the glass rod is rubbed with silk, work is done to overcome friction, providing energy for electrons to move.
Protons, which carry a positive charge $+1e$, are bound tightly within the nucleus and do not move during this process.
Since the glass rod becomes positively charged, it must have lost negative electrons $-1e$ to the silk cloth.
This leaves the rod with a net positive charge due to an excess of protons compared to the remaining electrons.
Therefore, the correct explanation is that negative charges moved from the glass rod to the silk cloth.
▶️ Answer/Explanation
Detailed solution:
Charging by friction occurs when two insulators are rubbed together, causing a transfer of surface particles.
In solids, protons and neutrons are bound tightly within the nucleus and cannot move between objects.
Only electrons, which carry a negative charge of approximately $-1.6 \times 10^{-19} \text{ C}$, are mobile enough to be transferred.
When the plastic rod becomes positively charged, it means it has lost some of its negative electrons to the rubbing material.
This creates an imbalance where the number of positive protons exceeds the remaining negative electrons.
Therefore, the only particles transferred during this charging process are electrons.