🔍 Key Concepts

• Thyristor (SCR) conduction depends on both the anode–cathode voltage and the gate signal. • The device must be forward biased between anode and cathode before a gate pulse can latch it on. • The gate voltage is referenced to the cathode, so its polarity is important.

💭 Think About

• Look at figure A and note which terminal is marked positive and which is negative. Under those markings, is the anode–cathode path forward or reverse biased? • For the gate to turn the device on, should the gate be driven more positive or more negative than the cathode, given the way they are marked in the figure? • Eliminate any choices where the anode–cathode polarity would leave the thyristor reverse biased, because in that condition it will not conduct even with a gate pulse.

✅ Before You Answer

• Verify which side of the symbol is anode (A or AO) and which is cathode (K) in figure A and the polarity symbols shown beside them. • Confirm the gate (G) polarity marking in the figure relative to the cathode terminal. • Before choosing, rule out all answers where the anode–cathode relationship is reverse biased; a thyristor will not conduct in that condition regardless of the gate pulse.