Find the currents

(a) In fig1, both diodes D₁ and D₂ are forward biased. So, resistance due to diodes=0.
Net resistance = 2Ω
Net current = 2V/2Ω = 1A

(b) In fig2, diode D₁ is forward biased and D₂ is reverse biased. So, no current will flow through this circuit because D₂ will offer infinite resistance.
Net current = 0A

(c) In fig3, diode D₁ and D₂, both are forward biased, So, resistance due to diodes=0.
Net resistance = 2Ω
Net current = 2V/2Ω = 2A

(d) Diode D₁ is forward biased and D₂ is reverse biased. So current will flow through D₁ but not through D₂.
Net resistance = 2Ω
Net current = 2V/2Ω = 2A