To calculate the net electric field at point [tex]\( P \)[/tex] due to two charges [tex]\( Q_1 \)[/tex] and [tex]\( Q_2 \)[/tex], we need to consider the vector sum of the electric fields produced by each charge at point [tex]\( P \)[/tex].
Given:
- The electric field due to charge [tex]\( Q_1 \)[/tex] ([tex]\( E_1 \)[/tex]) is [tex]\( 1.5 \times 10^5 \)[/tex] newtons/coulomb.
- The electric field due to charge [tex]\( Q_2 \)[/tex] ([tex]\( E_2 \)[/tex]) is [tex]\( 7.2 \times 10^5 \)[/tex] newtons/coulomb.
Since point [tex]\( P \)[/tex] is exactly between the two charges, and assuming the fields are along the same line, the net electric field at point [tex]\( P \)[/tex] is the sum of the magnitudes of these fields.
1. First, identify the magnitudes of the electric fields:
[tex]\[
E_1 = 1.5 \times 10^5 \; \text{newtons/coulomb}
\][/tex]
[tex]\[
E_2 = 7.2 \times 10^5 \; \text{newtons/coulomb}
\][/tex]
2. To find the net electric field, we add these two magnitudes together:
[tex]\[
\text{Net electric field} = E_1 + E_2
\][/tex]
[tex]\[
\text{Net electric field} = (1.5 \times 10^5) + (7.2 \times 10^5)
\][/tex]
3. Calculate the sum:
[tex]\[
\text{Net electric field} = 8.7 \times 10^5 \; \text{newtons/coulomb}
\][/tex]
Therefore, the correct answer is:
[tex]\[ \boxed{8.7 \times 10^5 \; \text{newtons/coulomb}} \][/tex]
So, the correct choice is:
[tex]\[ \text{D. } 8.7 \times 10^5 \text{ newtons/coulomb} \][/tex]
