Chapter 4: Q35E (page 843)

The power rating of a light bulb (such as a 100-W bulb) is the power it dissipates when connected across a 120-V potential difference. What is the resistance of (a) a 100-W bulb and (b) a 60-W bulb? (c) How much current does each bulb draw in normal use?

Short Answer

Expert verified

The resistance of 100-W bulb is $144 Ω$ .
The resistance of 60-W bulb is $240 Ω$ .
The current drawn by each bulb is 0.833 A and 0.500 A.

Step by step solution

Determination of the resistance of 100-W and 60-W bulbs.

The connection of the bulb is across a 120-V potential difference.

The expression of power is,

$P = \frac{V^{2}}{R}$

Solve for R and 100 W bulb,

role="math" localid="1655719758468" $R = \frac{V^{2}}{P} = \frac{{(120 V)}^{2}}{(100 W)} = 144 Ω$

Repeat the calculation for 60 W bulb,

$R = \frac{V^{2}}{P} = \frac{{(120 V)}^{2}}{(60 W)} = 240 Ω Thus, the resistances for 100 - W bulb is and for 60 W bulb is 144 Ω and for 60 W bulb is 240 Ω$

(b) Determination of the current drawn by each bulb is

Use the Ohm’s Law

$V = lR l = \frac{V}{R} For the 100 W bulb : l = \frac{(120 V)}{(144 Ω)} = 0.833 A For the 60 W bulb : l = \frac{(120 V)}{(240 Ω)} = 0.500 A Thus, the current drawn by 100 - W bulb and the 60 - W bulb is 0.833 A and 0.500 A$

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The power rating of a light bulb (such as a 100-W bulb) is the power it dissipates when connected across a 120-V potential difference. What is the resistance of (a) a 100-W bulb and (b) a 60-W bulb? (c) How much current does each bulb draw in normal use?

Short Answer

Step by step solution

Determination of the resistance of 100-W and 60-W bulbs.

(b) Determination of the current drawn by each bulb is

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