You have built a device that measures the temperature outside and displays it on

Question

You have built a device that measures the temperature outside and displays it on a dial as a measure of how far away from room temperature outside is. The way the dial works is that a needle with a charged ball on the end is placed between two charged parallel plates. The strength of the uniform electric field between the plates is proportional to the outside temperature. Given that the charged ball on the needle has a charge of -2.9 mu C and the needle can be represented as a string with tension 0.350 N, and is at an angle of 15degree, consider the following. What is the mass of the object? G What is the magnitude of the electric field?

Explanation / Answer

Given

   charge q = -2.9*10^-6 C
   Tension in the string is T = 0.350 N

   angle theta with thenormal is = 15 degrees

   from the free body diagram we can write the forces acting along

X direction is T sin theta -Eq = 0

Y direction is T cos theta - mg = 0

mass of the object is m = T cos theta /g

substituting the values

           m = 0.350*cos15 /9.8 kg

           m = 0.034497351 kg
           m = 34.5 grams

magnitude of the electric field is E = T sin theta /q

           E = 0.350*sin15/(2.9*10^-6) N/C

           E = 31236.78 N/C

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