Question

Two electric bulbs of 50 watt and 100 watt are given. which one will be brighter when they are connected (a) in series, and (b) in parallel?

Answer 1

Answer:

Explanation:Rating of bulbs hasn't been specified which is very important. Let's assume each bulb is rated at 120V,50Hz supply. Now what it means is that when 40W (or 60W) bulb will be connected across rated voltage i.e.120V ac supply then power dissipation across it will be 40W (or 60W). Rating is important because say if 40W bulb rated at 120V supply is connected across 220V supply then it will not work (might burn or blow up), meaning thereby a device can not work at a voltage much higher than its rated voltage.

One more information that you get from rating is the resistance of each bulb.

P=(V*V)/R

Since both bulbs are rated at same voltage, we can say that resistance of each bulb is inversely proportional to its rated power. Therefore

R (40W bulb) > R (60W bulb)

We should know that the bulb across which power dissipation is more will glow brighter. Now

1. When connected in series: In a series connection, current flowing across each element is same. So when 40W bulb and 60W bulb are connected in series, same current will flow through them. To find which bulb will glow brighter we need to find the power dissipation across each of them. From the relation

P=(I*I) R

since current is same we can say that power dissipation will be higher for the bulb with higher resistance i.e. 40W bulb.

Hence 40W bulb will glow brighter in series connection.

2. When connected in parallel: In a parallel connection, voltage across each element is same. So when 40W bulb and 60W bulb are connected in parallel, voltage across them will be same (100 V in the given case). To find which bulb will glow brighter we need to find the power dissipation across each of them. From the relation

P=(V*V)/R

since voltage is same we can say that power dissipation will be higher for the bulb with lower resistance i.e. 60W bulb.

Hence 60W bulb will glow brighter in parallel connection.

Answer 2

Answer:

Electric bulbs are connected in two different ways including series and parallel.

Explanation:

Current in parallel circuit is more than current in series circuit beacuse  the potential difference across each of the resistors that make up the circuit is the same.

a) When the bulb are connected in series, 100 watt bulb will glow brighter as the current remain same.

B) When bulb will be placed in parallel the bulb consuming less power will glow bighter because the bulb consuming more power (high volatge) will have higher resistance and it'scurrent will be less. Hence, the bulbs of 50watt will glow brighter.

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