We are on project in 'Introduction to electric circuit' class and we can use limited devices(resistance, op amp).
At first we intended to activate motor by signal from microphone sensor. But actually motor has 1 ohm, so when we connected power supply or op amp to motor there is no voltage drop on motor. How can we activate circuit or make voltage drop on 1 ohm when there are other resistances?

 

Welcome to AAC!

Generic opamps can only sink or source about 20mA. When you require more, you can add buffers to increase drive or you can have the low power opamp output drive a device that can switch the larger current required by the motor.

 

For an amplifier you can thry this audio amplifier. Its offset voltage is lower than some small opamps.
TDA2030