### Short Question Solution

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#### Kinematics

Introduction to Kinematics

# Electrostatics - Short Question Answers 2

1. Why are the tires of an airplane made of special rubber which are good conductor of electricity?
When the plane starts to land, friction is produced between the tire and the runway and the ground which produces charge. More accumulation of charge can cause sparkling and fire and pose threat to the passengers. So, the tires are made slightly conducting so the charge leaks to the ground ensuring safety of passenger and pilot as well as the property.

2. Define one electron volt.
The amount of kinetic energy gained by an electron while accelerating through potential difference of one volt is called 1 electron volt. It is denoted by eV.
1eV = unit electron charge * 1 volt
= 1.6 * 10-19 * 1
= 1.6 * 10-19J

3. What is meant by relative permittivity? What is its minimum value?
Dielectric constant or relative permittivity of a medium is defined as the ratio of permittivity of the medium to the permittivity of free space or vacuum. It is defined by εr is given by
εr = permittivity of medium / permittivity of free space
or, εr = ε/ε0
It is also called as dielectric constant (k). thus, the dielectric constant of a medium is the relative permittivity of medium with respect to the vacuum. The minimum value of dielectric constant or relative permittivity is 1 for vacuum or air and greater than 1 one for other medium.

4. If the electric field is zero throughout a certain region of space, is the potential also zero in the region or not? Explain.
The Electric field intensity and potential are related as
E = dV/dr, if E = 0, V = constant.
Thus, the electric potential may be non-zero, if the electric field is zero throughout a certain region like equipotential surface where its value is non-zero remains constant.

5. Sharp pointed projections are avoided in machines, why?
According to action of point, the surface charge density is inversely proportional to surface charge density due to which there is maximum surface charge density at points and when air molecules get in contact it gets similar charge and repels away. Similarly, another molecule comes near and repels in the same way. This phenomenon repeats with every molecule around the projection which leads to leaking of charge in continuous manner and formation of electric wind. This is why, sharp pointed projections are avoided in machines.

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