Finding the mass of a particle, when its charge is known

AI Thread Summary
The discussion centers on calculating the mass of a latex sphere suspended between metal plates, where the electric force balances the gravitational force. The electric force is given as 3.6 × 10^−14 N, which equals the weight of the sphere. To find the mass, one must relate weight to mass using the equation weight = mass × gravity. Participants clarify that the mass can be found by dividing the electric force by the acceleration due to gravity (approximately 9.8 m/s²). The correct mass of the sphere is determined to be 3.7 × 10^-15 kg.
bobsmith76
Messages
336
Reaction score
0

Homework Statement



A small latex sphere experiences an electric force of 3.6 × 10^−14 N when suspended halfway between a pair of large metal plates, which are separated by 48.0 mm. There is just enough electric force to balance the force of gravity on the sphere.
(a) What is the mass of the sphere?

Homework Equations



q = (mgΔd)/V

F (electrostatic force) = kq/r^2

The Attempt at a Solution



I have two unknowns in my first equation, q and V. My attempt to find q fails because I get a number that is around 10^-27. So if my number for q is wrong, then my number for V will also be wrong.
 
Physics news on Phys.org
bobsmith76 said:

Homework Statement



A small latex sphere experiences an electric force of 3.6 × 10^−14 N when suspended halfway between a pair of large metal plates, which are separated by 48.0 mm. There is just enough electric force to balance the force of gravity on the sphere.
(a) What is the mass of the sphere?

Homework Equations



q = (mgΔd)/V

F (electrostatic force) = kq/r^2

The Attempt at a Solution



I have two unknowns in my first equation, q and V. My attempt to find q fails because I get a number that is around 10^-27. So if my number for q is wrong, then my number for V will also be wrong.

I assume that's just the first part of the question, because it's actually very simple. You're given the electric force and told that it exactly balances the gravitational force (which is the weight). So in essence, you're told the weight of the sphere. How do you relate weight to the mass?
 
Ok, I multiplied 3.7 * 10^-15 by 9.8 and got the correct answer. Thanks.
 
bobsmith76 said:
My book says the answer is 3.7 * 10^-15. I don't see how they get that.

I repeat (from my earlier post):

So in essence, you're told the weight of the sphere. How do you relate weight to the mass?
 
bobsmith76 said:
Ok, I multiplied 3.7 * 10^-15 by 9.8 and got the correct answer. Thanks.

Sure, but to go the "right way" (to get the mass given the weight), you must divide by g (which is close to 9.8ms^{-2}.
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Closest distance of approach between 2 charged particles
Replies
5
Views
1K
Find net velocity of charged particle in electric field (symbols only)
Replies
14
Views
3K
Kinetic and potential energy of a particle attracted by charged sphere
Replies
6
Views
2K
Newton's shell theorem - all mass is concentrated at its centre
Replies
16
Views
1K
Investigating the Charge Distribution on a Bulging Sphere
Replies
18
Views
2K
Electrodynamics: charge of a particle
Replies
25
Views
2K
(Help) Surface charge density (σ) for particle to hit plate...
Replies
4
Views
990
Why Is Work Positive When Done Against the Electric Field?
Replies
22
Views
3K
Electric force due to a moving charge
Replies
7
Views
2K
Find the amount of work to move a particle from point A to B
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top