What Happens to the Brightness of a Bulb in a Series Circuit? Easiest Explanation

In a series circuit, as more light bulbs are added, the brightness of each bulb depends on the bulb ratings and circuit voltage. When bulbs of similar rating are connected in series circuit, their brightness decreases proportionally. However, if their rating is different, then the bulb of lower rating will glow brighter.

Analyzing basic electrical principles reveals how brightness changes in series circuits. So, let’s dig deeper into the mechanics of voltage distribution and its impact on individual bulb brightness.

Current and Resistance Impact Brightness

In a series circuit, the current is constant through all components. Bulb brightness depends on the power dissipated, which is current squared times resistance.

P=I²R

For two different bulbs, the one with higher resistance will dissipate more power and appear brighter, assuming equal current.

Bulbs of Identical Ratings Connected in Series

When bulbs of identical ratings are connected in series, their resistances add. So, if the current decreases but the voltage stays the same, the power P dissipated in each bulb decreases. Since the bulbs are identical, they share the current equally. And with equal lower currents, the power and brightness of each bulb decrease by the same amount.

Let’s assume each bulb has the following ratings: 

Power (P) = 100W 

Voltage (V) = 220V 

According to Ohm’s law:

R = V/I

For a 100W, 220V bulb: 

P = IV

or, 100W = I x 220V 

or, I=100W/220V = 0.45A

Again,

                                                            R =V/I

                                                               =220V/0.45A

                                                               = 490 Ω

When connected in series: 

R_Total = R₁ + R₂

                                                            = 490Ω + 490Ω

                                                          = 980Ω

Using Ohm’s Law: 

I = V/R_Total = 220V/980Ω = 0.22A

With the lower series current of 0.22A, the power in each bulb is: 

P = I x V = (0.22A)*(220V) = 48.4 W

So, the power has dropped from 100W to 48.4W per bulb. Since power corresponds to brightness, the bulbs will be dimmer, with equal dimness in both bulbs.

Bulbs of Different Ratings Connected in Series

When bulbs of different wattage are connected in series, the lower wattage bulb has higher resistance. With the same current, more power is dissipated in the higher-resistance bulb, making it brighter than the higher-wattage bulb. 

Let’s assume each bulb has the following ratings: 

Bulb 1 (50W) P₁ = 50W 

V₁ = 220V 

Bulb 2 (100W) P₂ = 100W 

V₂ = 220V 

For series connection: 

Total voltage, V_Total = V₁ + V₂

                       = 220V + 220V

       = 440V

Using power formula: For 50W bulb,

Power (P) = Current (I) x Voltage (V)

P₁ = I x V₁  

Or, P₁= I x 220V

Or, I =50/220

= 0.227A

Same current through both bulbs since they are in series. Now, resistance 

R₁ = V₁/I = 220V/0.227A = 969Ω (for 50W bulb)

R₂ = V₂/I = 220V/0.227A = 969Ω (for 100W bulb)

P₁ = (0.227)² x 969 = 50W

P₂ = (0.227)² x 969= 50W

Since power dissipated is proportional to brightness: Bulb 1 (50W) will glow brighter than Bulb 2 (100W) when connected in series. This is because the higher resistance Bulb 1 has greater voltage drop (220V) compared to Bulb 2’s smaller voltage drop.

Frequently Asked Questions (FAQs)

1. Can the Bulbs be Brighter by Adding More Batteries in a Series Connection?

Answer: Yes, adding more battery voltage in series will make the bulbs brighter. More total voltage allows a higher voltage drop across each bulb, increasing the power dissipation and brightness.

2. Can the Bulbs Become Dimmer if Lower Wattage Bulbs Are Used in Series?

Answer: Yes, lower-wattage bulbs will be dimmer in a series circuit because they have higher resistance. According to Ohm’s law, higher resistance means less current for the same voltage. Less current results in less power dissipated and a dimmer bulb.

3. What Happens if One Bulb Burns Out in a Series Circuit?

Answer: If one bulb burns out and opens the circuit, the current will stop flowing, and all the bulbs will turn off. This is because the complete loop is needed for current in a series circuit.

To conclude 

Understanding this phenomenon has real-world applications. Proper bulb selection and voltage regulation maintains brightness in multi-bulb installations. It highlights the importance of circuit designing, where the relationship between voltage, current, and resistance must be finely balanced.