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

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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