Instantaneous power in an AC circuit is defined as .

here are the answers to the questions:

7. Instantaneous power in an AC circuit is defined as _________

Instantaneous power in an AC circuit is the product of the instantaneous voltage (EMF) across the circuit element and the instantaneous current flowing through it. This is represented by the formula $P(t) = V(t) \cdot I(t)$.

The correct option is C.

$$\boxed{\text{C. the product of the instantaneous EMF and instantaneous current flowing through it.}}$$

8. The field lines shown in the figure below shows _________

The field lines in the figure originate from one point and terminate on another, indicating two opposite charges. The symmetrical pattern of the field lines suggests that the magnitudes of these charges are equal.

The correct option is B.

$$\boxed{\text{B. electric field lines for two charges of equal magnitude but opposite charges}}$$

9. As electric force is parallel to electric field lines, magnetic force is _________

The electric force on a charge is always in the same direction as the electric field lines. However, the magnetic force on a moving charge is given by the Lorentz force law, $\vec{F} = q(\vec{v} \times \vec{B})$, which means the magnetic force is always perpendicular to both the velocity of the charge and the magnetic field lines.

The correct option is D.

$$\boxed{\text{D. perpendicular to magnetic field lines}}$$