Self Test on Tutorial 10

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Answer

For the mains, the potential difference changes direction with a frequency of …………. Hz

 

This means that one complete cycle takes time T =

 

 

The potential difference is given as ……….. V. In fact the peak p.d., V0­, is more like 325V

 

Label the two axes with the quantities that can be measured with the CRO

 

 

 

The average p.d would be …………. but this is not very useful – energy is obviously being transferred so, to get some idea of an ‘average’, it is useful to look at the power delivered.

 

Heating effect

 

Power  P = IV =

 

For the peak current, I0 =

 

If I = 0, power =

 

The mean power =

 

Show these quantities on the axes

 

 

 

 

 

The root mean square value of I for a.c. Irms, is the current (dc) that would give the same power as the mean (ac) power

 

        Irms 2  =

 

         Irms   =

 

Also   Vrms =                              eg for the mains, V0  = 325 V  so Vrms =