Consider four masses arranged (clockwise from A at the top) in a cross (looks like a giant plus symbol). Each is 1cm from the center of the cross. Mass A has a charge +1𝜇C , mass B has a charge of −1𝜇C , and mass C has a charge of +2𝜇C . At the center the electric field points 30 degrees (Northeast) from the vertical axis.

Is there a formula I need to find the missing value of D? I tried setting opposite ends equal to separate and find D but I cant figure this out or find anything online like it. Thank you.

look at the relative field strengths (at the center) from the individual charges

... they are all one cm away
... so the contribution to the net field is proportional to the charge

north-south is +1 N

east-west is ... D - 1 E

(E-W) / (N-S) = tan(30º)

To find the missing value of D, we can use the concept of electric field and superposition. The electric field at the center of the cross is caused by the electric fields produced by each individual charge.

First, let's find the electric field at the center of the cross produced by charge A. The electric field due to a point charge at a distance (r) from it is given by the formula:
E = k * (q / r^2)
where E is the electric field, k is the Coulomb's constant (8.99 x 10^9 Nm^2/C^2), q is the charge, and r is the distance from the charge.

For charge A (1μC), it is at a distance of 1cm = 0.01m from the center. Therefore, the electric field due to charge A at the center is:
E_A = k * (q_A / r_A^2) = (8.99 x 10^9 Nm^2/C^2) * (1 x 10^-6 C) / (0.01m)^2

Similarly, we can find the electric field at the center of the cross due to charges B and C using the same formula.

Next, since the electric field is a vector quantity, we need to consider the direction of the electric field produced by each charge. For charge A, it points 30 degrees northeast from the vertical axis. For charges B and C, their locations and electric fields can be used to determine the direction using vector addition.

Now, at the center of the cross, the total electric field is the vector sum of the electric fields produced by each charge. If we know the magnitude and direction of the total electric field at the center, we can break it down into horizontal and vertical components.

Finally, using the components of the electric field and the distances of the charges from the center, we can set up equations based on the principle of superposition to solve for the missing value of D.

Keep in mind that the problem mentioned four masses, but it only specified the charges for three of them (A, B, and C). Make sure all the relevant information is provided for a complete solution.