HS2 Physics Chapter 7 ALTERNATING CURRENT: Experiments

 

Experiment Title: Alternating Current

Aim:

To study the characteristics of alternating current and verify the relationship between root mean square (rms) value and peak value of AC voltage.

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Apparatus Required:

• Step-down Transformer

• AC Voltmeter

• DC Voltmeter

• Milliammeter

• Resistor (Load)

• Diode (for rectification)

• CRO (Cathode Ray Oscilloscope)

• Connecting Wires

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Theory:

Alternating current (AC) varies sinusoidally with time and is given by:
$I(t) = I_0 \sin(\omega t)$

Where:

• $I_0$ is the peak current,

• $\omega = 2\pi f$ is the angular frequency.

The root mean square (rms) value of AC is:
$I_{rms} = \frac{I_0}{\sqrt{2}}$

For voltage:
$V_{rms} = \frac{V_0}{\sqrt{2}}$

This experiment also explores rectification (conversion of AC to DC) and filtering.

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Procedure:

Part A: Observation of AC Waveform

1. Connect the step-down transformer to the AC mains.

2. Connect the secondary coil of the transformer to the CRO.

3. Switch on the transformer and observe the waveform on the CRO screen.

4. Measure the peak voltage $V_0$ using the vertical scale of the CRO.

5. Calculate the rms voltage using:
   $V_{rms} = \frac{V_0}{\sqrt{2}}$

Part B: Verification using AC Voltmeter

6. Connect an AC voltmeter across the transformer secondary.

7. Record the reading of the voltmeter (which gives $V_{rms}$).

8. Compare this value with the calculated $V_{rms}$ from the CRO observation.

Part C: Rectification and Filtering

9. Connect a diode in series with a resistor to form a half-wave rectifier circuit.

10. Connect this circuit to the transformer output.

11. Use a DC voltmeter across the resistor to measure the rectified DC voltage.

12. To observe the filtered output, connect a capacitor in parallel with the resistor and note the change in output waveform on the CRO.

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Observations:

Record values of:

• Peak Voltage from CRO

• RMS Voltage (Calculated and Measured)

• DC Output Voltage (Rectified)

• Waveform shape before and after filtering

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Calculations:

Compute:

• RMS voltage from peak voltage

• % error between measured and calculated values

• DC output with and without filtering

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Result:

• The rms value of AC is verified to be $\frac{V_0}{\sqrt{2}}$

• The AC waveform, rectified output, and filtered output were successfully observed and recorded