B

Step 1: Understanding the Circuit
We have a series circuit consisting of a capacitor and an inductor (coil). When connected to an AC source (the mains), the circuit will exhibit a certain power factor, which is defined as cos φ, where φ is the phase difference between the voltage and current.

Step 2: Power in AC Circuits
The power (P) consumed in an AC circuit is given by:
$$ P = V I ext{cos} heta $$
where:

• V is the voltage across the source,
• I is the current,
• cos θ is the power factor.

Since the problem states that the heat power generated in the coil increased by a factor of n = 1.7, we have:
$$ P' = 1.7 P $$

Step 3: Relationship Between Power Factor and Current
When the capacitance is varied, the current in the circuit and the power factor (cos φ) will also change. We can express the new power as:
$$ P' = V I' ext{cos} heta' $$
In the absence of exact values for voltage or current, we can analyze the relationship:
$$ P' = 1.7 P = V I ext{cos} heta' $$

Step 4: Current and Power Factor Change
Since P increases while voltage remains constant, the current also has to change. Let us denote the initial current as I and the new current as I'.
$$ I' = k I $$
for some factor k (which is also related to the changes in cos φ). Thus, we can substitute this into P' equation to find:
$$ 1.7 P = V (k I) ext{cos} heta' $$
The ratio of the powers gives:
$$ rac{P'}{P} = 1.7 = rac{k ext{cos} heta'}{ ext{cos} heta} $$

Step 5: Calculating the Change in Power Factor
With the stated relationship:
$$ k ext{cos} heta' = 1.7 ext{cos} heta $$
This indicates that both the power factor and the multiplicative current effect are contributing to this overall increase. The final change in cos φ shows that as we increase cos φ, we represent it as a percentage change:
$$ rac{ ext{cos} heta' - ext{cos} heta}{ ext{cos} heta} imes 100 ext{ ext{percent}} $$
Based on the context of simple circuits, moving from a lower to higher power factor will yield an approximate percentage change result.

Conclusion
Through the calculations and the nature of the changes in both current and voltage relationships, we can conclude that the change in cos φ was approximately 10%. Hence the closest option is:
Option B.