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Solve the following.
An electric bulb is marked 200V, 100W. Calculate electrical resistance of its filament. If five…
An electric bulb is marked $200\text{V}, 100\text{W}$. Calculate electrical resistance of its filament. If five such bulbs are connected in series to a $200\text{V}$ supply, how much current will flow through them?
Answer
Answer
Formulas used: Electric power: P = V*I with P = 100 W, V = 200 V, so R = 400 ohm Resistors in series: R = R1 + R2 + R3 with R1 = 400 ohm, R2 = 400 ohm, R3 = 1200 ohm, so R = 2000 ohm Ohm's law: V = I*R with R = 2000 ohm, V = 200 V, so I = 0.1 A
Given: $V = 200\text{ V}$, $P = 100\text{ W}$.
Resistance of the filament: $R = \frac{V^2}{P} = \frac{200^2}{100} = 400\text{ }\Omega$.
Five bulbs in series: $R_s = 5 \times 400 = 2000\text{ }\Omega$, so $I = \frac{V}{R_s} = \frac{200}{2000} = 0\cdot1\text{ A}$.
Final answer: $R = 400\ \Omega,\ I = 0.1\text{ A}$