00:01
For this problem on the topic of electrostatics, we have two small spheres, each with a mass of 0 .1 grams, suspended by pendulums, which are made from light insulating strings at a common point as shown in the figure.
00:13
They are given the same electric charge, and they come to equilibrium when each string is an angle of three degrees with a vertical.
00:19
If the length of each string is one meter, we want to find the magnitude of the charge on each of the spheres.
00:24
Now we'll first draw the free body diagram of the sphere on the right, as we have shown here, and then we'll look at newton's second law in component form.
00:36
Firstly, the resultant force in the horizontal direction, the x direction, is equal to the electric force qe minus the horizontal component of tension t sine theta, and we know that from newton's second low, this must equal the mass of the sphere times the x component of acceleration.
01:00
Now we know that this is equal to zero since the sphere is in equilibrium, which means that the electric force qe is equal to the horizontal component of tension t sine theta.
01:13
For the y component, we can do the same.
01:16
The sum of the vertical forces is the y component of the tension t cosine theta minus the weight of the sphere, which is its mass times the acceleration due to gravity...