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Opamp used as a voltage-controlled current source

The current flow in the collector and emitter will be the same. The current in the lamp and R1 will therefore also be the same. The voltage across R1 depends on the current flowing in it; this voltage will therefore also depend on the current flow in the lamp.

The opamp will try to keep Vn=Vp. This means that the current flow though the lamp depends on the voltage at the non-inverting input of the opamp. Because R1 is 1 ohm, a 1V voltage will cause a 1A current flow. The voltage across R1 will also be 1V, which leaves 11V for the lamp. R1 dissipates 1W.

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