Which light bulb will glow brighter 60 watt or 100 watt when connected in series ?

A 60-watt bulb will glow brighter. When connecting two lamps in series, the electric current will be the same in both lamps. However, the voltage is divided between them in proportion to their resistance.

And in the case of parallel connection, the higher wattage bulb will glow brighter. For example, we do parallel connection in house wiring, so we can see in our home that the higher wattage bulb always glows brighter.

Note: we do house  wiring connections in parallel because If one electrical appliance stops working due to some defect/short circuit, then all remaining appliances keep working normally. And in parallel connection its easiest to find a foults.

Let's figure out by calculation which bulb will glow brighter 

• To calculate the resistance of each bulb, we can use the formula for electrical power: 

P = V^2 / R 

• Where, P is the power in watts, V is the voltage in volts, and R is the resistance in ohms. 

• We know that the 60 W bulb has a known power and resistance. To find a resistance, we can rearrange a formula: 

R = V^2/ P

 For a 60 W bulb: R1 = (220^2)/ 60 = 806.67 ohms

•  Now, let's calculate the resistance of the 100 W bulb:

For a 100 W bulb: R2 = (220^2)/ 100 = 484 ohms

• When connecting the two lamps in series, the total resistance will be the sum of the individual resistances:

 Total resistance = R1 + R2 = 806.67 +484 = 1290.67 ohms 

• The electric current in the network will be determined by the total network voltage divided by the total resistance: 

I = Total voltage / Total resistance 

I=  220 / 1290.67 = 0.1701A 

• Now, we can calculate the voltage across each bulb using the voltage formula: 

V = I*R 

For a 60 W bulb: V1 = 0.1701 * 806.67 = 137.29 V 

              For a 100 W bulb: V2 = 0.1701 * 484 =  82.29 V

So its clear from the above calculation that 60 watt bulb has larger voltage as compared to 100 watt bulb therefore 60 watt bulb will glow more brighter when connected in series.

                                                                                 OR

By calculating power dissipation accross both lamps we can figure out which bulb will glow brighter: 

Power dissipation accross 60 watt bulb : 

i².R = (0.1701)²*806.67 = 23.34 watt

Power dissipation accross 100 watt bulb : 

I².R = (0.1701)² * 484  = 14.00 watt

After calculating dissipation power we can clearly see that power dissipation 60 watt bulb is higher than 100 watt bulb thus higher power dissipation means  brighter the bulb will glow .

Which bulb will glow brighter When 60 watt and 100 watt bulb conned in parallel

 When these bulb are connected in parallel, voltage across both bulb is same and power consumption will be V^2/R. In this case bulb with low resistance will consume more power and glow brighter than the bulb with high resistance, in this case 100 watt bulb have lower resistance ( because power is inversely proportional to resistance so higher the power lower the resistance value ) therefore 100W bulb will glow brighter than 60W bulb.

General rule : 

When we connect two bulbs or more than two bulbs in the series, the bulb which has lower power rating have more resistance and it will glow brighter & in case of parallel connection the bulb which has higher power rating have more resistance and it will glow brighter .