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    Hi, i dont get root mean squared values at all so i was wondering if anyone could help me understand root mean squared values of a sinusoidal wave.

    Specifically where resistors are involved.

    E.g. i have a question here where i dont know how to even start!

    A sinusoidal alternating voltage which has an rms value of 230V is connected to a 60(ohms) heating element designed to operate at an rms value of 230V. Calculate

    the peak voltage

    The voltage change from positive peak to negative peak

    The rms current

    The peak current

    The peak power

    The mean power

    Thanks in advance
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    (Original post by chemicalX)
    Hi, i dont get root mean squared values at all so i was wondering if anyone could help me understand root mean squared values of a sinusoidal wave.

    Specifically where resistors are involved.

    E.g. i have a question here where i dont know how to even start!

    A sinusoidal alternating voltage which has an rms value of 230V is connected to a 60(ohms) heating element designed to operate at an rms value of 230V. Calculate

    the peak voltage

    The voltage change from positive peak to negative peak

    The rms current

    The peak current

    The peak power

    The mean power

    Thanks in advance
    The peak value of current or voltage is the rms value x √2
    This is a relationship you should know.

    AC voltages and currents are usually quoted as rms values. For example, your mains domestic voltage supply, given as 240V, will be 240 V rms.
    The peak value will be 240 √2 (about 339V)

    You just use V=IR in this question to find unknown currents or voltages.
    You can use peak or rms in the equation so long as you use the same for both current and voltage.
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    (Original post by chemicalX)
    Hi, i dont get root mean squared values at all so i was wondering if anyone could help me understand root mean squared values of a sinusoidal wave.

    Specifically where resistors are involved.

    E.g. i have a question here where i dont know how to even start!

    A sinusoidal alternating voltage which has an rms value of 230V is connected to a 60(ohms) heating element designed to operate at an rms value of 230V. Calculate

    the peak voltage

    The voltage change from positive peak to negative peak

    The rms current

    The peak current

    The peak power

    The mean power

    Thanks in advance
    Peak voltage swing = 2 x root2 x r.m.s.

    +ve pk to -ve pk = root2 x r.m.s

    I = VR

    so for rms current use rms voltage and resistance

    for peak current use pk voltage and resistance

    P = V2/R or I2R

    So for peak power use the peak voltage or current

    Mean Power is the average continuous power. So use either rms voltage or current.
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    (Original post by uberteknik)
    Peak voltage swing = 2 x root2 x r.m.s.

    +ve pk to -ve pk = root2 x r.m.s

    I = VR

    so for rms current use rms voltage and resistance

    for peak current use pk voltage and resistance

    P = V2/R or I2R

    So for peak power use the peak voltage or current

    Mean Power is the average continuous power. So use either rms voltage or current.
    (Original post by Stonebridge)
    The peak value of current or voltage is the rms value x √2
    This is a relationship you should know.

    AC voltages and currents are usually quoted as rms values. For example, your mains domestic voltage supply, given as 240V, will be 240 V rms.
    The peak value will be 240 √2 (about 339V)

    You just use V=IR in this question to find unknown currents or voltages.
    You can use peak or rms in the equation so long as you use the same for both current and voltage.

    Hi sorry i know this is off topic but what is meant when a fully charged capacitor is discharged through a resistor with a time constant of 0.2ms?

    is it thaat the charge will fall to 37% of its original value in 0.2ms? if it is why is it correct? to me it seems right but i dont know why!?

    Thank you

    PS your other explanation helped a lot!
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    (Original post by chemicalX)
    Hi sorry i know this is off topic but what is meant when a fully charged capacitor is discharged through a resistor with a time constant of 0.2ms?

    is it thaat the charge will fall to 37% of its original value in 0.2ms? if it is why is it correct? to me it seems right but i dont know why!?

    Thank you

    PS your other explanation helped a lot!
    It's a result of the fact that when a capacitor C discharges through a resistor R the amount of charge on that capacitor falls exponentially (like radioactive decay) according to the formula

    Q=Qo e (-t/CR)

    This means that if t = CR then
    Q=Qoe-1
    or
    Q=Qo/e
    or Q=0.37Qo as 1/e = 0.37

    The value of t that equals CR is called the time constant of the circuit.
 
 
 
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