The oscilloscope screen trace is shown when it is linked to a d.c. supply that is being turned on and off. The Y-gain control setting and the time base control setting are given. The supply voltage is $v$. The supply is turned on $f$ times each second. What are the values of $v$ and $f$?
- A$v = 2\ \text{V},\ f = 50$
- B$v = 2\ \text{V},\ f = 100$
- C$v = 4\ \text{V},\ f = 50$
- D$v = 4\ \text{V},\ f = 100$