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Edexcel A Level Physics:復(fù)習(xí)筆記7.22 Root-Mean-Square Current & Potential Difference

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年10月12日上午9:29

Root-Mean-Square Current & Potential Difference

The root-mean-square (rms) current?Irms?is defined by the equation:

7.10.1-I-rms-Equation

Where:
- I0?=?peak current?(A)

The rms voltage?Vrms?is defined by the equation:

7.10.1-V-rms-Equation

Where:
- V0?=?peak voltage?(V)
Rms current is equal to?0.707I0, which is about?70%?of the peak current?I0
- This is also the case for rms voltage

Worked Example

An electric oven is connected to a 230 V root mean square (rms) mains supply using a cable of negligible resistance.

Calculate the peak-to-peak voltage of the mains supply.

Step 1: Write down the Vrms?equation

7.10.1-V-rms-Equation

Step 2: Rearrange for the peak voltage,?V0

V0?= √2 × Vrms

Step 3: Substitute in the values

V0?= √2 × 230

Step 4: Calculate the peak-to-peak voltage

- The peak-to-peak voltage is the peak voltage (V0) × 2

Peak-to-peak voltage = (√2 × 230) × 2 = 650.538 =?651 V (3 s.f)

Exam Tip

You are expected to know how to apply these equations, which simply relate the peak current or voltage of an AC circuit to its rms value.

Remember, the rms value in an AC circuit is?equivalent to values of current and voltage that would produce the same heating effect in DC circuits. This means, you can use the rms values in AC circuits for equivalent calculations involving DC circuits.

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