Question

Four bulbs of 10w,20w,30,and 40w are connected in series which bulb will shine more.which will shine more when connected in parallel??

Answer 1

1. The 10 W bulb will shine brightest.

B. The 40 W bulb will shine brightest.

Explanation:

1. Series connection:
   Series is not the normal way for these to be connected. The brightest will not be the one that would normally be brightest. Let the voltage the bulbs are intended to be applied to them be `E`. Ohm's Law can be used to give us 3 versions of the formula for power. They are

`P = E*I = E^2/R = I^2*R`

Let's look at the 10 W bulb and the 40 W bulb. Those bulbs were made to be used with a certain voltage. Just unscrew one bulb from a lamp and put in one with a different power rating. Voltage does not change in that process.

Since `P = E^2/R, " ""Resistance" = E^2/P`.

So the 10 W bulb's resistance will be more than the 40 W bulb's resistance. In fact the 10 W bulb has 4 times as much resistance. Resistance is a characteristic of the bulb. It does not change whether connected in series or parallel.

In a series connection, a single current passes thru each bulb. That current will be

`I_"series" = E/"total resistance"`

But the voltage across the bulbs will not be the full `E` the bulb was made for. They each will consume less power than if they were connected normally.

But, back to comparing the 10 W bulb and the 40 W bulb. They both have the same current. We found above that the 10 W bulb had more resistance. Looking at the formula

`P = I^2*R`,

since the 10 W bulb's resistance is greater, the power dissipated in it will be greater. Therefore it will shine brightest.

B. Parallel connection:

When in parallel connections, the bulbs are in their normal situations and will each consume power according to their power ratings. So the 40 W bulb will consume 40 Watts of power and shine brightest.

I hope this helps,
Steve