Question

Common transparent tape becomes charged when pulled from a dispenser. If one piece is placed above another, the repulsive force can be great enough to support the top piece's weight. Assuming equal point charges (only an approximation), calculate the magnitude of the charge if electrostatic force is great enough to support the weight of a 12.0 mg piece of tape held 1.10 cm above another. (The magnitude of this charge is consistent with what is typical of static electricity.)

Answer 1

Sol. : To hold the upper layer in air, the electrostatic force must be equal to the gravitational force.

Considering charge is same on both layers, we have

where Q is the charge on each layer (to be calculated)

r is the distance between both layers, (given) = 1.10 10^-2m

Mass of uper layer = m =12 10^-6 kg

K and g are electrostatic and gravitational constants respectively.

Putting all the values, we get

Coloumb

Q = 1.25710^-9C or 1.257nC

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