iGCSE Physics (0625) 4.2.1 Electric charge -Exam Style Questions Paper 2 - New Syllabus
▶️ Answer/Explanation
Detailed solution:
In a solid metal sphere, only the negative charges (free electrons) are mobile, while the positive charges (protons) remain fixed within the atomic lattice.
When the negatively charged rod is brought near the sphere, it exerts an electrostatic force on the particles.
According to the fundamental laws of electrostatics, like charges repel each other.
Therefore, the negatively charged rod repels the negatively charged free electrons within the metal.
These electrons are pushed away towards the far side of the sphere, leaving a deficiency of electrons on the near side.
Consequently, a net positive charge develops on the surface of the sphere closest to the negatively charged rod.
▶️ Answer/Explanation
Detailed solution:
When a positively charged balloon is brought near a neutral wall, it induces a charge on the surface of the wall.
According to the fundamental law of electrostatics, opposite charges attract while like charges repel.
The positive charge on the balloon exerts an attractive force on the negatively charged electrons within the atoms of the wall.
This attraction pulls the electrons closer to the surface of the wall, creating a local negative charge layer.
The electrostatic force of attraction between the positive balloon and these negative electrons is strong enough to make the balloon stick.
Therefore, the statement that positive charges on the balloon attract electrons in the wall correctly explains the observation.
▶️ Answer/Explanation
Detailed solution:
Charging by friction involves the transfer of $electrons$ between two insulating materials.
Protons are bound tightly within the nucleus and do not move during the charging process.
An object becomes negatively charged if it gains $electrons$, which carry a relative charge of $-1$.
In this case, friction causes $electrons$ to move from the cloth onto the plastic rod.
Since the rod now has an excess of negative charges, its net charge becomes negative.
Therefore, the rod becomes negatively charged because it gains $electrons$.