Question

What must the charge (sign and magnitude) of a 1.65 gg particle be for it to remain balanced against gravity when placed in a downward-directed electric field of magnitude 640 N/CN/C ?

Answer 1

Answer:

Charge, $q=2.52\times 10^{-5}\ C$ and it is negative.

Explanation:

Given that,

Mass of the charge, $m=1.65\ g=1.65\times 10^{-3}\ kg$

Electric field, E = 640 N/C

To find,

Charge

Solution,

The electric force and the force of gravity are balanced in the electric field. It is given by :

$qE=mg$

$q=\dfrac{mg}{E}$

$q=\dfrac{1.65\times 10^{-3}\times 9.8}{640}$

$q=2.52\times 10^{-5}\ C$

Since, the electric field is in downward direction. The force must be upward direction s that the charge is negative.    

Answer 2

Answer:

- 2.53 x 10^-5 C

Explanation:

Electric field, E = 640 N/C downward

mass of particle, m = 1.65 g = 1.65 x 10^-3 kg

Let the charge is q.

The electrostatic force is balanced by the weight of the particle.

As the weight is downward so the electrostatic force should be upward, as the electric field is downwards so the sign of charge is negative.

q E = m g

q x 640 = 1.65 x 10^-3 x 9.8

q = 2.53 x 10^-5 C

Thus, the charge is 2.53 x 10^-5 C and it is negative in nature.