Q. 275.0( 1 Vote )

# When a (60 W, 220V) bulb and a (100 W, 220 V) bulb are connected in series, then which bulb will glow brighter?

**OR**

In a voltmeter, there are 20 divisions between the 0 mark and 0.5 V mark. Calculate the least count of the voltmeter.

Answer :

By knowing the resistance of each bulb, we can know that which bulb will glow brighter. Higher the resistance, brighter the bulb will glow.

__I case: Bulb A____(60 W, 220V)__

Given: Power = 60W

Voltage = 220V

To calculate the resistance by the formula V = IR, first, we need to find out the current flowing in the bulb. Apply the formula:

P = VI

•

• I = 0.27A

Now apply the formula:

V = IR

•

• R = 814.8 ohm

__Thus, the resistance of the bulb A is 814.8 ohm.__

__II case: Bulb B____(100 W, 220V)__

Given: Power = 100W

Voltage = 220V

To calculate the resistance by the formula V = IR, first, we need to find out the current flowing in the bulb. Apply the formula:

P = VI

•

• I = 0.45A

Now apply the formula:

V = IR

•

• R = 488.8 ohm

__Thus, the resistance of the bulb B is 488.8 ohm.__

The resistance of the bulb A is higher. Hence it will glow more brighter than bulb B.

**OR**

It is given that in a voltmeter there are 20 divisions between the 0 mark and 0.5 V mark.

Given: Number of divisions = 20

Distance between the two marks = 0.5V – 0V = 0.5V

We need to find out the least count of a voltmeter.

** Least count:** The smallest measured value of any instrument is said to be the least count of that instrument. It is measured as:

• Least count of voltmeter = 0.025V

__Thus, the least count of the given voltmeter is 0.025V.__

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