Define alternating current .

An alternating current periodically varies from positive to negative and changes its magnitude continuously with time, with its direction reversing every half-cycle.

Define peak current ( I 0 ).

Peak current is the maximum value of the alternating current.

The variation of alternating current or voltage with time can be described as a .......... curve.

The variation of alternating current or voltage with time can be described as a sinusoidal curve.

True or False? Mains electricity is supplied as direct current.

False. Mains electricity is supplied as alternating current — this is the type of current produced by power stations and supplied to sockets.

How do electrons in a wire carrying alternating current move?

They move back and forth with simple harmonic motion .

Define the r.m.s. value of an alternating current.

The value of a constant (direct) current that produces the same power in a resistor as the alternating current.

The r.m.s. current is equal to 0.707 × I 0 , which is about .......... % of the peak current.

The r.m.s. current is equal to 0.707 × I 0 , which is about 70 % of the peak current.

True or False? A direct voltage produces a different amount of heating in a resistor compared to an alternating voltage of the same r.m.s. value.

False. The r.m.s. value is defined so that it delivers the same average power (heating effect) in a resistor as an equivalent steady direct current or voltage.

Define a resistive load .

A resistive load is an electrical component with resistance, for example a lamp.

True or False? For an alternating supply, the power delivered to a resistor is constant with time.

False. The power varies constantly with time, since current and voltage are constantly varying; the mean power is used as an average measure over a full cycle.

A LevelPhysicsCambridge (CIE)Flashcards21. Alternating CurrentsCharacteristics of Alternating Currents

Characteristics of Alternating Currents (Cambridge (CIE) A Level Physics): Flashcards

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FrontAlternating Current & Voltage
Define alternating current.

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Cards in this collection (18)

Define alternating current.
An alternating current periodically varies from positive to negative and changes its magnitude continuously with time, with its direction reversing every half-cycle.
Define peak current (I₀).
Peak current is the maximum value of the alternating current.
What equation gives the value of an alternating current I at any time t?
$I = I_{0} \sin (ω t)$
How is angular frequency ω related to time period T and frequency f?
$ω = \frac{2 π}{T} = 2 π f$
The variation of alternating current or voltage with time can be described as a .......... curve.
The variation of alternating current or voltage with time can be described as a sinusoidal curve.
True or False?
Mains electricity is supplied as direct current.
False.
Mains electricity is supplied as alternating current — this is the type of current produced by power stations and supplied to sockets.
How do electrons in a wire carrying alternating current move?
They move back and forth with simple harmonic motion.
Define the r.m.s. value of an alternating current.
The value of a constant (direct) current that produces the same power in a resistor as the alternating current.
What is the equation for r.m.s. current I_r.m.s in terms of peak current I₀?
$I_{r . m . s} = \frac{I_{0}}{\sqrt{2}}$
What is the equation for r.m.s. voltage V_r.m.s in terms of peak voltage V₀?
$V_{r . m . s} = \frac{V_{0}}{\sqrt{2}}$
The r.m.s. current is equal to 0.707 × I₀, which is about .......... % of the peak current.
The r.m.s. current is equal to 0.707 × I₀, which is about 70 % of the peak current.
True or False?
A direct voltage produces a different amount of heating in a resistor compared to an alternating voltage of the same r.m.s. value.
False.
The r.m.s. value is defined so that it delivers the same average power (heating effect) in a resistor as an equivalent steady direct current or voltage.
Define a resistive load.
A resistive load is an electrical component with resistance, for example a lamp.
How does the mean power delivered to a resistive load compare to the peak power, for a sinusoidal alternating supply?
$P_{m e a n} = \frac{P_{p e a k}}{2}$
The mean power is half the peak (maximum) power.
What is the equation for mean power in terms of r.m.s. current?
$P_{m e a n} = (I_{r . m . s})^{2} R$
What is the equation for peak power in terms of peak current I₀?
$P_{p e a k} = (I_{0})^{2} R$
For direct current and voltage, power can be written as P = IV = I²R = ..........
For direct current and voltage, power can be written as P = IV = I²R = $\frac{V^{2}}{R}$
True or False?
For an alternating supply, the power delivered to a resistor is constant with time.
False.
The power varies constantly with time, since current and voltage are constantly varying; the mean power is used as an average measure over a full cycle.

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