## Question

- Diagram 4.1 shows four diodes connected to an alternating current supply. The output terminal X and Y across the resistor R are connected to a cathode ray oscilloscope (CRO). The time base of the CRO is set at 0.01s/division. Diagram 4.2 shows the trace obtained on the screen of the CRO.

Rajah 4.1 menunjukkan 4 diod disambung kepada bekalan kuasa arus ulang alik. Terminal-terminal output X dan Y merentasi perintang R disambung kepada sebuah osiloskop sinar katod (OSK). Dasar masa OSK itu dilaras kepada 0.01s/bahagian. Rajah 4.2 menunjukkan surihan yang diperolehi pada skrin OSK itu.

### Answer

Hi Farhaini,

In Diagram 4.2, the trace represents the **current after rectification**, where the current only travels in one direction.

For an alternating current (with no rectification or before rectification), the trace on a CRO would be in a wave pattern. Before rectification, the a.c. trace looks like this, where the current is traveling in one direction in the first half of the cycle and the opposite direction in the second half of the cycle. Hence for every second half of the cycle, you can see that the shape is reflected downwards.

1 division actually means 1 box on the CRO.

1 cycle of the a.c. occupies 2 boxes, which is 2 divisions.

(You can think of division as something like length)

The time base is given by the question, which is 0.01s/division. So we multiply the number of divisions in one cycle with the time base to find the period of the a.c. Here, you notice that the â€śdivâ€ť unit cancels off.

2div \times 0.01s\space div^{-1}=0.02s

So if we have an a.c. supply but we donâ€™t know the frequency of the a.c supply, we will connect the a.c. supply to a CRO, and use the same method to find the frequency by first finding the period, then we would just use the formula Frequency=\frac{1}{Period}

Hope this helps!

Ohhhh I see Thank you very much !