Figure below shows an op-amp amplifier. Find the output voltage in steady state condition where $$(i)$$ switch is open $$(ii)$$ $$S$$ is closed

A practical $$R$$-$$C$$ sinusoidal oscillator is built using a positive feedback amplifier with a closed loop gain slightly less than unity.

In the transistor circuit shown in figure. Collector to ground voltage is $$+20V.$$ Which of the following is the probable cause of error?

Given figure, shows a non - inverting op - amp summer with $${V_1} = 2\,V$$ and $${V_2} = \, - 1V.$$ The output voltage $${V_0} = \_\_\_\_\_$$