# Calculating the charge to mass ratio

1. Jan 31, 2016

### WestTXcollegekid

1. The problem statement, all variables and given/known data
A small object with mass m, charge q, and initial speedv0 = 5.00×10^3 m/s is projected into a uniform electric field between two parallel metal plates of length 26.0 cm (Figure 1) .The electric field between the plates is directed downward and has magnitude E = 700 N/C . Assume that the field is zero outside the region between the plates. The separation between the plates is large enough for the object to pass between the plates without hitting the lower plate. After passing through the field region, the object is deflected downward a vertical distance d = 1.15 cm from its original direction of motion and reaches a collecting plate that is 56.0 cm from the edge of the parallel plates. Ignore gravity and air resistance.

2. Relevant equations
E=F/q
xf=xi+vi*t+(1/2)at^2

3. The attempt at a solution

Since gravity and air resistance air are not factors, I thought the only thing affecting the motion of the object is the electric field. Using the horizontal velocity, I calculated the time that the object was between the plates. Then, using that and the second equation I calculated the vertical acceleration of the object. From there, I expanded the first equation into E=(m*a)/q and plugged in the acceleration and given electric field and solved for q/m

#### Attached Files:

• ###### Screen Shot 2016-01-30 at 8.41.20 PM.png
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2. Jan 31, 2016

### Staff: Mentor

I don't see a question. Did you obtain a result or are you just outlining an approach you tried? How did it turn out? Did it go off the rails somewhere?

3. Jan 31, 2016

### haruspex

Your method, as far as you describe it, sounds right. Not clear what you did in regard to the travel after the plates. Please post your working. Please keep it symbolic (no plugging in numbers) until the final step.

4. Jan 31, 2016

### WestTXcollegekid

The objective is to find the charge to mass ratio, I have attached a screenshot of the problem.

5. Jan 31, 2016

### WestTXcollegekid

The issue I'm having is, how do i go about finding the y velocity after it exits the E field. and how do I find the acceleration on the object by the E field if i don't know the displacement during its time in the E field.

6. Jan 31, 2016

### haruspex

Let the acceleration in the field be a. Calculate where it should end up on the screen in terms of a.

7. Jan 31, 2016

### Staff: Mentor

Since these things depend upon quantities you don't know (the mass and charge), you should leave them as variables.

Edit: Note that the problem wants you to find the ratio q/M. Figure that at some point you'll be able to insert some variable (maybe call it "r") to represent q/M. I'd take a look at your acceleration and see what it depends on.

8. Feb 13, 2016

### ur sh

A small object with mass m, charge q, and initial speed v0 = 6.00×103 m/s is projected into a uniform electric field between two parallel metal plates of length 26.0 cm (Figure 1) . The electric field between the plates is directed downward and has magnitudeE = 700 N/C . Assume that the field is zero outside the region between the plates. The separation between the plates is large enough for the object to pass between the plates without hitting the lower plate. After passing through the field region, the object is deflected downward a vertical distanced = 1.35 cm from its original direction of motion and reaches a collecting plate that is 56.0 cm from the edge of the parallel plates. Ignore gravity and air resistance. Calculate the object's charge-to-mass ratio, q/m. can anyone help me with this ques plz

9. Feb 13, 2016

### Staff: Mentor

ur sh,

If you want help with the same problem, then you'll have to supply your own attempt at a solution first. The Original Poster in this thread still has not solved the problem, so getting him/her to the finish line will take priority if he/she returns.

Note that according to the forum rules, no help can be offered until an attempt at solution has been made.

10. Feb 13, 2016

### ur sh

A small object with mass m, charge q, and initial speed v0 = 6.00×103 m/s is projected into a uniform electric field between two parallel metal plates of length 26.0 cm (Figure 1) . The electric field between the plates is directed downward and has magnitudeE = 700 N/C . Assume that the field is zero outside the region between the plates. The separation between the plates is large enough for the object to pass between the plates without hitting the lower plate. After passing through the field region, the object is deflected downward a vertical distanced = 1.35 cm from its original direction of motion and reaches a collecting plate that is 56.0 cm from the edge of the parallel plates. Ignore gravity and air resistance.
Calculate the object's charge-to-mass ratio, q/m.
but this ans is wrong
E=F/q
700=F/q
700q*82=1/2mv^2
2*700*82/(6*10^3)=(1400*82)?36*10^6
32*10^-4

11. Feb 13, 2016

### Staff: Mentor

You'll have to explain your logic. What does your third step represent?

12. Feb 16, 2016

### Blueyblue

Hmm, how does he get 82?

13. Mar 3, 2016

### kristinxamber

82 is the total distance travelled by the particle