Electrical Math
Electrical Math
Ohm’s Law-2
What is the peak-to-peak RF voltage on the 50 ohm output of a 100 watt transmitter?
What is the peak-to-peak RF voltage on the 50 ohm output of a 100 watt transmitter?
200 volts
From haihuynh8108:
\begin{align} E &= \sqrt{P \times R}\\ &= \sqrt{100\text{ watts}\times 50\text{ ohms}}\\ &= \sqrt{5,000\text{volts}}\\ \ V_{\text{RMS}} &= 70.71\text{ volts}\\ \end{align}
[B] Next, multiply the \(V_{\text{RMS}}\) by \(2\sqrt{2}\) to find the peak-to-peak voltage:
\begin{align}
V_{\text{pk-pk}} &= V_{\text{RMS}} \times 2\sqrt{2}\\
&= 70.71 \times 2\sqrt{2}\\
&\approx 200 \text{ volts}\\
\end{align}
References:
Circuit Digest, "RMS Voltage Calculator"
OneChip, "RMS<->Peak<->P-P"
[Rev. B] Format modified
[Rev. C] Added reference
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What is the maximum DC or RMS voltage that may be connected across a 20 watt, 2000 ohm resistor?
What is the maximum DC or RMS voltage that may be connected across a 20 watt, 2,000 ohm resistor?
200 volts.
From wp2ahg:
\begin{align} E &= \sqrt{P \times R}\\ &= \sqrt{20\text{ watts}\times 2,000\text{ ohms}}\\ &= \sqrt{40,000\text{volts}}\\ &= 200\text{ Volts}\\ \\ \end{align}
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A 500-ohm, 2-watt resistor and a 1500-ohm, 1-watt resistor are connected in parallel. What is the maximum voltage that can be applied across the parallel circuit without exceeding wattage ratings?
A 500-ohm, 2-watt resistor and a 1500-ohm, 1-watt resistor are connected in parallel.
What is the maximum voltage that can be applied across the parallel circuit without exceeding wattage ratings?
31.6 volts.
From kd7bbc:
First find the max voltage of each resistor.
\begin{align} E_1 &= \sqrt{P_1 \times R_1}\\ &= \sqrt{500 \times 2}\\ &= 31.6V\\ \\ E_2 &= \sqrt{P_2 \times R_2}\\ &= \sqrt{1500 \times 1}\\ &= 38.7V \end{align}
\(R_1\) has a lower max voltage and thus will limit the voltage to a max of \(31.6V\)
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In Figure 3B1, what is the voltage drop across R1?
In Figure 3B1, what is the voltage drop across R1?
5 volts
From badwolf.j.:
The voltage drop across a resistor is equal to the proportion of the resistor to the total resistance in the circuit multiplied by the voltage.
Voltage Drop across R1 = (R1 ÷ RT) ∗ V
Voltage Drop across R1 = (300 Ω ÷ 600 Ω) ∗ 10 V
Voltage Drop across R1 = 0.5 ∗ 10
Voltage Drop across R1 = 5 volts
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In Figure 3B2, what is the voltage drop across R1?
In Figure 3B2, what is the voltage drop across R1?
9 volts.
Due to 3V Zener diode,
the 12 volts − 3 volts = 9 volts
IF NO ZENER diode, then the following would be the calculation.
The voltage drop across a resistor is equal to the proportion of the resistor to the total resistance in the circuit multiplied by the voltage.
Voltage Drop across R1 = (R1 ÷ RT) ∗ V
Voltage Drop across R1 = (10K Ω ÷ 25K Ω) ∗ 12 V
Voltage Drop across R1 = 0.4 ∗ 12
Voltage Drop across R1 = 5 volts
For explanation of the effect Zener diodes on circuits, please see All About Circuits site for the article What Are Zener Diodes? Chapter 3 - Diodes and Rectifiers
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What is the maximum rated current-carrying capacity of a resistor marked “2000 ohms, 200 watts”?
What is the maximum rated current-carrying capacity of a resistor marked “2000 ohms, 200 watts”?
(A). 0.316 amps
From wp2ahg:
Square Root in Amperes of Power in Watts divided by Resistance in Ohms.
\begin{align} I &= \sqrt{P \div R}\\ \\ \end{align}
\begin{align} I &= \sqrt{200\text{watts}\div 2,000\text{ohms}}\\ & \ \\ &= \sqrt{0.1\text{ohms}}\\ & \ \\ &= 0.316\text{ amps} \\ \end{align}
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