or
Subelement B
Electrical Math
Section 10
Ohm’s Law-2
What is the peak-to-peak RF voltage on the 50 ohm output of a 100 watt transmitter?
• 70 volts.
• 100 volts.
• 140 volts.
200 volts.

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}}\\ &= 70.71\text{ Volts}\\ \\ \end{align}

Next,
(Eeff=rms)

• Emax/ Eeff = 2√2 or
• Vp-p/ Vrms = 2√2
• Vp-p = (70.71 volts) ∗ (2√2) =200 volts

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What is the maximum DC or RMS voltage that may be connected across a 20 watt, 2000 ohm resistor?
• 10 volts.
• 100 volts.
200 volts.
• 10,000 volts.

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{200\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?
• 22.4 volts.
31.6 volts.
• 38.7 volts.
• 875 volts.

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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Tags: none In Figure 3B1, what is the voltage drop across R1?
• 9 volts.
• 7 volts.
5 volts.
• 3 volts.

In Figure 3B1, what is the voltage drop across R1?

5 volts

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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Tags: none In Figure 3B2, what is the voltage drop across R1?
• 1.2 volts.
• 2.4 volts.
• 3.7 volts.
9 volts.

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”?
0.316 amps.
• 3.16 amps.
• 10 amps.
• 100 amps.

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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