AC Circuits Flashcards

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1
Q

An alternating current is

A

The current that waves periodically with time in direction

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2
Q

What is the root mean square of an alternating current or voltage?

A

The value of the steady current/voltage that would dissipate heat as the alternating current/voltage in a resistive load

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3
Q

The transformer is a device that..

A

Is used to change the alternating voltage to a larger or smaller value

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4
Q

Rectification is

A

The process of converting an alternating current to a direct current

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5
Q

Define the period of an alternating current

A

The time taken for the completion of one cycle of the a.c.

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6
Q

Define frequency of an alternating current.

A

Number of complete cycles on the a.c. per unit time

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7
Q

Define the alternating frequency of a current

A

The frequency in hertz multiplied by 2π radians per cycle

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8
Q

Define the peak value of an alternating current

A

The maximum value (in terms of magnitude) of the a.c. for one cycle.

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9
Q

Describe the use of a laminated core in a transformer

A

To reduce energy loss due to heat by reducing the size of induced/eddy currents in the core, thus reducing power loss due to heat dissipated.

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10
Q

Describe the use of a soft iron core in a transformer

A

To strongly concentrate the magnetic field in the core to increase flux linkage and minimize flux LEAKAGE

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11
Q

How does a transformer work?

A
  • an alternating e.m.f. applied across the primary coil produces an alternating current in the primary coil.
  • this sets up a varying magnetic field which cuts the secondary coil due to the presence of the soft iron core.
  • there will be a change in magnetic flux linkage in the secondary coil, and by Faraday’s law of electromagnetic induction, an alternating e.m.f. is induced across the secondary coil.
  • as the rate of change of magnetic flux linkage alternates due to the primary current, the e.m.f. induced in the secondary coil will be alternating.
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12
Q

What is an ideal transformer?

A

A transformer that is 100% efficient and has no power losses.

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13
Q

Define direct current

A

A current with one direction only since the polarity of the d.c. supply remains constant with time.

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14
Q

Why is there a heating effect on a coil connected to alternating current even though the average current in the heating coil is 0?

A

For a sinusoidal a.c., although the average current is zero over one cycle, current would still pass through the heating coil, independent of the currents direction, causing electrical energy to be converted to thermal energy throughout the cycle.

Hence a heating effect is produced in the coil which depends on the r.m.s. current rather than the average current.

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