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What must the charge (sign and magnitude) of a particle of mass 1.42 g be for it

ID: 1645043 • Letter: W

Question

What must the charge (sign and magnitude) of a particle of mass 1.42 g be for it to remain stationary when placed in a downward-directed electric field of magnitude 600 N/C? Use 9.81 m/s^2 for the magnitude of the acceleration due to gravity. What is the magnitude of an electric field in which the electric force on a proton is equal in magnitude to its weight? Use 1.67 times 10^-27 kg for the mass of a proton, 1.60 times 10^-19 C for the magnitude of the charge on an electron, and 9.81 m/s^2 for the magnitude of the acceleration due to gravity.

Explanation / Answer

A)

m = mass of the charge = 1.42 g = 1.42 x 10-3 kg

E = electric field = 600 N/C

q = magnitude of the charge

for the charge to be stationary , the electric force on the charge by the electric field must balance the weight of the charge

hence

qE = mg

q (600) = (1.42 x 10-3) (9.81)

q = 2.32 x 10-5 C

The electric force on the charge must be in upward direction to balance the weight in down direction

As we can see , electric force on the charge is upward while the electric field is downward. hence the charge experience electric force in opposite direction of electric field which is a characteristic of a negative charge.

hence charge is negative

B)

m = mass of the proton = 1.67 x 10-27 kg

q = charge on proton = 1.6 x 10-19 C

E = electric field = ?

for the charge to be stationary , the electric force on the charge by the electric field must balance the weight of the charge

hence

qE = mg

(1.6 x 10-19 ) E = (1.67 x 10-27) (9.81)

E = 1.02 x 10-7 N/C

The electric force on the charge must be in upward direction to balance the weight in down direction

As we can see , electric force on the charge is upward and the charge on proton is positive. hence the charge experience electric force in same direction of electric field which is a characteristic of a positive charge.

hence electric field is upward.

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