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Point Charge Check!?
Hi, I' did this problem but for some reason I'm not getting the right answer. If you could check to see where I made my mistake I'd really appreciate it. Thanks!
The problem:
A poitn charge (m=1 g) at the end of an insulating string of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of 12000 N/C where the pendulum's position is as shown in the figure, with the charge 12 cm above the lowest (vertical ) position. If the field points to the right, determine the magnitude and sign of the point charge.
My Answer:
I know the charge is postive because it is repelled by the electric force.
Because the system is in equilibirum, I know that
Ftx = Fe (force of the elctric field)
Fty = mg
Fty = mg
= (.001 kg) (9.8)
=.0098
To find Ftx we need the angle.
theta = invscos (43/53)
theta = 35.77
Fty = Ft cos (35.77)
.0098 = Ft cos (35.77)
Ft = 0.012078
Ftx = 0.012078 sin 35.77
Ftx = 0.00706
Fe = 0.00706
Fe = qE
0.00706 = q * 12000
q = 5.88 * 10 ^-7
Correct Answer is : 7.8 * 10 ^-7
Hi, I' did this problem but for some reason I'm not getting the right answer. If you could check to see where I made my mistake I'd really appreciate it. Thanks!
The problem:
A poitn charge (m=1 g) at the end of an insulating string of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of 12000 N/C where the pendulum's position is as shown in the figure, with the charge 12 cm above the lowest (vertical ) position. If the field points to the right, determine the magnitude and sign of the point charge.
My Answer:
I know the charge is postive because it is repelled by the electric force.
Because the system is in equilibirum, I know that
Ftx = Fe (force of the elctric field)
Fty = mg
Fty = mg
= (.001 kg) (9.8)
=.0098
To find Ftx we need the angle.
theta = invscos (43/53)
theta = 35.77
Fty = Ft cos (35.77)
.0098 = Ft cos (35.77)
Ft = 0.012078
Ftx = 0.012078 sin 35.77
Ftx = 0.00706
Fe = 0.00706
Fe = qE
0.00706 = q * 12000
q = 5.88 * 10 ^-7
Correct Answer is : 7.8 * 10 ^-7