H12-311_V3.0 · Question #311
Which of the following is correct about power calculation? (Multiple choice)
The correct answer is A. 0 dBm = 1 mW B. 3dBm = 2mW D. 27dBm = 500mW. A, B, and D are correct because they follow the dBm formula: P(mW) = 10^(dBm/10), where 0 dBm is anchored to 1 mW by definition (A), +3 dBm doubles power so 3 dBm ≈ 2 mW (B), and 27 dBm = 30 dBm − 3 dBm = 1000 mW ÷ 2 = 500 mW (D). Option C is wrong because 10 dBm = 10^(10/10) =…
Question
Which of the following is correct about power calculation? (Multiple choice)
Options
- A0 dBm = 1 mW
- B3dBm = 2mW
- C10dBm = 100mW
- D27dBm = 500mW
How the community answered
(32 responses)- A72% (23)
- C28% (9)
Explanation
A, B, and D are correct because they follow the dBm formula: P(mW) = 10^(dBm/10), where 0 dBm is anchored to 1 mW by definition (A), +3 dBm doubles power so 3 dBm ≈ 2 mW (B), and 27 dBm = 30 dBm − 3 dBm = 1000 mW ÷ 2 = 500 mW (D). Option C is wrong because 10 dBm = 10^(10/10) = 10^1 = 10 mW, not 100 mW - 100 mW would be 20 dBm.
Memory tip - the "3/10 rule": Starting from 0 dBm = 1 mW, every +10 dBm multiplies power by 10, and every +3 dBm doubles power. So 10 dBm = 10 mW, 20 dBm = 100 mW, 30 dBm = 1000 mW; and 3 dBm = 2 mW, 27 dBm = (30 − 3) dBm = 1000 ÷ 2 = 500 mW.
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