Concept & Reasoning

This is a pure resistive-network question, so VAB is obtained from the equivalent resistance between terminals A and B. The vertical 5 Ω and 10 Ω resistors prevent treating the two outer paths as simple independent series branches; the network must be reduced using node-voltage/bridge transformation or solved by applying a test voltage/current. If a 1 V test source is applied across A-B and the resulting input current is calculated from nodal equations, Req is obtained as Vtest/Itest. Scaling to the specified 5 A terminal current then gives the terminal voltage. The official answer corresponds to Req ≈ 6.842 Ω and hence 34.21 V.

How to Solve It in the Exam

For a complicated passive network, apply a 1-V test source and solve nodal voltages; the input current immediately gives Req.

Important Exam Point

Do not combine resistors as series/parallel when their common node has another branch attached.

Quick Trick

For a complicated passive network, apply a 1-V test source and solve nodal voltages; the input current immediately gives Req.

Common Mistake

A bridge-looking network is not automatically balanced; verify balance conditions before removing the cross branch.

Concept & Reasoning

This is a pure resistive-network question, so VAB is obtained from the equivalent resistance between terminals A and B. The vertical 5 Ω and 10 Ω resistors prevent treating the two outer paths as simple independent series branches; the network must be reduced using node-voltage/bridge transformation or solved by applying a test voltage/current. If a 1 V test source is applied across A-B and the resulting input current is calculated from nodal equations, Req is obtained as Vtest/Itest. Scaling to the specified 5 A terminal current then gives the terminal voltage. The official answer corresponds to Req ≈ 6.842 Ω and hence 34.21 V.

How to Solve It in the Exam

For a complicated passive network, apply a 1-V test source and solve nodal voltages; the input current immediately gives Req.

Important Exam Point

Do not combine resistors as series/parallel when their common node has another branch attached.

Quick Trick

For a complicated passive network, apply a 1-V test source and solve nodal voltages; the input current immediately gives Req.

Common Mistake

A bridge-looking network is not automatically balanced; verify balance conditions before removing the cross branch.

Concept & Reasoning

This is a pure resistive-network question, so VAB is obtained from the equivalent resistance between terminals A and B. The vertical 5 Ω and 10 Ω resistors prevent treating the two outer paths as simple independent series branches; the network must be reduced using node-voltage/bridge transformation or solved by applying a test voltage/current. If a 1 V test source is applied across A-B and the resulting input current is calculated from nodal equations, Req is obtained as Vtest/Itest. Scaling to the specified 5 A terminal current then gives the terminal voltage. The official answer corresponds to Req ≈ 6.842 Ω and hence 34.21 V.

How to Solve It in the Exam

For a complicated passive network, apply a 1-V test source and solve nodal voltages; the input current immediately gives Req.

Important Exam Point

Do not combine resistors as series/parallel when their common node has another branch attached.

Quick Trick

For a complicated passive network, apply a 1-V test source and solve nodal voltages; the input current immediately gives Req.

Common Mistake

A bridge-looking network is not automatically balanced; verify balance conditions before removing the cross branch.