A plastic ruler rubbed against a woolen cloth will be charged because the friction between the two objects causes the transfer of electrons between them. When a plastic ruler is rubbed against a woolen cloth, the atoms in the materials interact, and the electrons between them can move from one material to another.
Plastic has a lower electron affinity than woolen cloth, so when rubbed, plastic tends to lose some electrons. Woolen cloth, on the other hand, tends to attract electrons from plastic, as its electron affinity is higher. As a result, the plastic becomes positively charged as it loses electrons, while the wool cloth becomes negatively charged as it gains more electrons.
This process is referred to as "charge transfer" or "static charging," and results in the plastic ruler and wool cloth becoming charged with different charges. This charge can cause the plastic ruler to attract small, oppositely charged objects, such as pieces of paper, because there is a force of attraction between differently charged charges.
What will happen if the ruler after being rubbed on the cloth - After the ruler is rubbed on the cloth, the ruler will become charged with a different electrical charge than its condition before rubbing.
If a plastic ruler is rubbed on a wool fabric, as explained earlier, the ruler will become positively charged as it loses some electrons. Meanwhile, the wool cloth will become negatively charged as it gains more electrons from the plastic ruler.
With a charged ruler, several effects are possible:
The ruler can attract small objects: A positively charged ruler will attract negatively charged objects, such as pieces of paper or strands of hair, because there is a pull force between the different charges.
The ruler can cause electric sparks to jump: If conditions are dry enough, the charge on a ruler can cause electric sparks to jump (likely to occur if the charge is very large).
Ruler can cause shock: If a person touches a ruler after rubbing it and there is a difference in electrical charge between their body and the ruler, there is a small shock due to static electricity.
A ruler can affect the surrounding electric field: A charged ruler will create an electric field around it, which can affect the behavior of nearby charged objects.
However, it is important to note that these effects may be more pronounced in dry conditions and if the resulting charge is large enough. Also, the static charge on the ruler will dissipate over time as the electric charge on the objects can be lost quickly through contact or environmental influences.