Introduction:
When light bulbs are connected in series, the same current flows through each bulb. However, the voltage across each bulb is different based on its power rating. In this scenario, three light bulbs with power ratings of 40W, 60W, and 100W are connected in series with a 220V power supply. The brightness of a bulb is directly proportional to its power consumption.

Calculating Current:
To determine the current flowing through the circuit, we can use Ohm's Law: V = I * R, where V is the voltage, I is the current, and R is the resistance. Since the bulbs are connected in series, the total resistance is the sum of the individual resistances of the bulbs. The resistance of a bulb can be calculated using the formula: R = (V^2) / P, where V is the voltage and P is the power rating of the bulb.

Let's calculate the resistance for each bulb:
- For the 40W bulb: R1 = (220^2) / 40 = 1210 ohms
- For the 60W bulb: R2 = (220^2) / 60 = 806.67 ohms
- For the 100W bulb: R3 = (220^2) / 100 = 484 ohms

The total resistance in the circuit is the sum of these individual resistances: R_total = R1 + R2 + R3 = 2500.67 ohms.

Now, we can calculate the current flowing through the circuit using Ohm's Law: I = V / R_total = 220 / 2500.67 = 0.0879 A.

Calculating Power Consumption:
Since the current is the same for all bulbs, the power consumed by each bulb can be calculated using the formula: P = I * V, where P is the power consumption, I is the current, and V is the voltage.

Let's calculate the power consumption for each bulb:
- For the 40W bulb: P1 = 0.0879 * 220 = 19.336 W
- For the 60W bulb: P2 = 0.0879 * 220 = 19.336 W
- For the 100W bulb: P3 = 0.0879 * 220 = 19.336 W

Conclusion:
From the calculations, we can see that all three bulbs have the same power consumption of 19.336W. Therefore, all three bulbs will have the same brightness when connected in series with a 220V power supply.