Physics 2

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Explain briefly the workings of electrical transformer, both step-up and step-down

In a step-up transformer, compare the secondary voltage and current to the corresponding primary values. Explain briefly how transformers minimize losses in long distance electrical circuits.

What is the relationship between kWh and Joules?

Explain briefly the difference between peaks and rms voltage.

In an AC circuit that contains a capacitor and an inductor, impedance replaces the DC concept of resistance. Explain briefly the difference between the two quantities.

An AC circuit with a variable frequency generator, a resistor, an inductor, and a capacitor has a resonant frequency, at which the maximum current flows. Explain

  • Physics 2 -

    1. The step-down transformer reduces the
    primary voltage by a factor equal to the
    turns ratio. For instance, if the turns ratio was 4:1, the voltage across the secondary would be 1/4 of the primary voltage. In a step-up transformer with
    a turns-ratio of 1:4, the voltage across
    the secondary would be four times the
    primary voltage.

    2. In a step-up transformer with a turns-ratio of 1:4, the secondary voltage will be 4 times the primary voltage. The secondary current will be
    1/4 of the primary current.

    In long distance electrical circuits, the step-up transformer is used to reduce the line current which reduces
    the I^2*R losses.

    3. 1kW = 1KJ/s
    1kWh = 1KJ/s*3600s
    1kWh = 3600kJ

    4. rms means root-mean-square and is 0.707 times the peak value.

    5. The impedance of a circuit is the ratio of the applied rms voltage to the
    resulting rms current(Vrms/Irms).

    The D.C. resistance is the ratio of the applied D.C. voltage to the resulting D.C. current(Vdc/Idc).

    6. At the resonant frequency, the reactance of the inductor and capacitor
    are equal and opposite. Therefore. the
    net reactance is zero. So the current is
    maximized and determined by the value of
    the resistor.

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