CFAA Fire Alarm Technician · Question
A 24VDC smoke detector is rated at 3.6 Watts. What is its equivalent internal resistance during its active state?
First, find current using I = P/V (3.6W / 24V = 0.15A). Then find resistance with R = V/I (24V / 0.15A = 160 Ohms). Alternatively, R = V^2 / P (576 / 3.6 = 160)
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Question: A 24VDC smoke detector is rated at 3.6 Watts. What is its equivalent internal resistance during its active state?
Answer options: ✅ 160 Ω
- 86 Ω
- 6.6 Ω
- 400 Ω
Correct answer: 160 Ω
Explanation: First, find current using I = P/V (3.6W / 24V = 0.15A). Then find resistance with R = V/I (24V / 0.15A = 160 Ohms). Alternatively, R = V^2 / P (576 / 3.6 = 160).
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Question explanations
- The primary power for a fire alarm system must be:
- If a 120VAC primary power circuit for a fire alarm control unit is consuming 60 Watts of power, what is the cu
- In a steady-state DC circuit, if the conductor length is doubled while maintaining voltage and wire gauge, wha
- A resistor is rated at 10 Watts at 24VDC. If the voltage drops to 20VDC, what is the new power dissipation?
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