Alternating Current vs Direct Current - Rms Voltage, Peak Current & Average Power of AC Circuits

Summary

This video explains the difference between DC (Direct Current) and AC (Alternating Current), covering essential concepts such as voltage, current, and their behavior over time. It details how to calculate RMS (Root Mean Square) and peak values for both voltage and current in AC circuits, and demonstrates real-world applications with examples like household power supplies and electronic devices. The video also walks through several practical calculations, including power consumption in devices like laptops and resistors, highlighting the relationship between RMS and peak values and their impact on power usage in AC circuits.

Takeaways

• 😀 DC (Direct Current) has constant voltage and current, whereas AC (Alternating Current) varies sinusoidally over time.
• 😀 In an AC circuit, voltage alternates in direction 60 times per second in North America, resulting in a frequency of 60 Hz.
• 😀 The peak voltage in an AC circuit is √2 times the RMS voltage. For 120 V RMS, the peak voltage is approximately 170 V.
• 😀 The RMS (Root Mean Square) current represents the effective value of current in an AC circuit and is calculated by dividing the peak current by √2.
• 😀 The average power in an AC circuit is calculated by multiplying RMS voltage and RMS current.
• 😀 The peak current in an AC circuit is √2 times the RMS current, which can be used to calculate other AC properties.
• 😀 The maximum power in an AC circuit is twice the average power and is calculated by multiplying peak voltage by peak current.
• 😀 For a 200 W laptop using a 240 V AC line, the RMS current is 0.8333 A, and the peak current is approximately 1.18 A.
• 😀 The peak voltage in a 240 V AC system is approximately 339.4 V, calculated by multiplying RMS voltage by √2.
• 😀 The average power absorbed by a resistor is calculated by squaring the RMS current and multiplying by resistance. For a 5 A current and 10 ohms resistance, the power absorbed is 250 W.
• 😀 The peak voltage across a resistor can be found by multiplying the RMS voltage by √2. For a 50 V RMS, the peak voltage is 70.7 V.

Q & A

What is the key difference between DC current and AC current?

DC current (direct current) has a constant voltage and current that flows in one direction, while AC current (alternating current) has a voltage that varies sinusoidally and the current oscillates, reversing direction at regular intervals.

How does the voltage behave in an AC circuit compared to a DC circuit?

In an AC circuit, the voltage varies sinusoidally over time, oscillating between positive and negative values. In contrast, DC voltage remains constant over time.

What is the RMS (Root Mean Square) voltage and how is it related to peak voltage in an AC circuit?

The RMS voltage is a measure of the effective voltage in an AC circuit, which is equivalent to the DC voltage that would deliver the same power. The peak voltage is related to the RMS voltage by the formula: peak voltage = RMS voltage × √2.

What is the formula for calculating the peak voltage from the RMS voltage?

The peak voltage (V_peak) is calculated using the formula: V_peak = √2 × V_RMS, where V_RMS is the RMS voltage.

If the RMS voltage of a typical household is 120V, what is the peak voltage?

The peak voltage is approximately 169.7V or about 170V, calculated as V_peak = √2 × 120V.

How do you calculate the RMS current from the peak current?

The RMS current is calculated as the peak current (I_peak) divided by the square root of 2, using the formula: I_RMS = I_peak / √2.

In a 200W laptop connected to a 240V AC line, how do you calculate the RMS current?

To calculate the RMS current, use the formula: P = V_RMS × I_RMS, where P is the average power (200W) and V_RMS is the RMS voltage (240V). The RMS current is calculated as I_RMS = 200W / 240V = 0.8333A.

What is the relationship between RMS current and peak current?

The peak current (I_peak) is related to the RMS current (I_RMS) by the formula: I_peak = √2 × I_RMS.

What is the maximum power in an AC circuit and how is it calculated?

The maximum power (P_max) is calculated by multiplying the peak voltage (V_peak) and peak current (I_peak): P_max = V_peak × I_peak. It is twice the average power in an AC circuit.

How do you calculate the average power absorbed by a resistor in an AC circuit?

The average power (P_avg) absorbed by a resistor is calculated using the formula: P_avg = I_RMS² × R, where I_RMS is the RMS current and R is the resistance.