Part A: A 75 W light bulb with a resistance of 177 ? is connected to a power sup

Question

Part A: A 75 W light bulb with a resistance of 177 ? is connected to a power supply with a 117 V. What is the internal resistance of the power supply? Express the answer with one decimal place.

Part B: A component with a 14 Ohm resistor is rated for use at power levels not exceeding 2,185 mW. How much current can safely flow through the component? Express the answer with two decimal places (even if the rounded number will be larger than the value of the safe current).

Part C: A power supply with internal resistance of 5 ? applies a voltage of 29 V. If a load resistor of 66 ? is in series with the power supply, then what is the current going through the circuit? Express the answer with two decimal places.

Thanks :)

Explanation / Answer

a)

equivalent resistance

Req =177+r

total current in the circuit

I=V/Req =117/117+r

P=I^2*R

75 =(117/(177+r))^2*177

(177+r) =179.74

r=2.74 ohms

r=2.7 ohms

b)

P=I^2*R

=>I =sqrt[P/R] =sqrt[2185*10^-3/14]

I=0.395 A

I=0.40 A (approx)

c)

equivalent resistance

Req= 5+66

Req =71 ohms

current

I=V/R =29/71

I=0.41 A

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