The ideal OP-AMP circuit shown in the Figure produces output voltage $V_o=x$ when the Switch, $S$, is open.

Which of the options represents the output voltage when S is closed?

Consider the circuit shown in the Figure with $V_i=3 \mathrm{~V}$ and $V_{c c}=12 \mathrm{~V}$. Assume $V_{B E}=0.7 \mathrm{~V}$ and $\beta_{\mathrm{dc}}=99$ for the BJT.

Which of the following options is the correct value of the current $I_o$ ?

A small signal source, $V_i(t)=A \cos \left(10^5 t\right)+B \sin \left(10^7 t\right)$ is applied to a BJT circuit as shown in the Figure.

Assume zero source resistance, $V_{B E}=0.7 \mathrm{~V}, \beta_{\mathrm{dc}}=99$, Early voltage $=100 \mathrm{~V}$ and Thermal voltage $=25 \mathrm{mV}$. Effect of internal parasitic capacitances of the BJT may be neglected. Which expression is the best approximation of the output voltage $V_o(t)$ ?

A circuit using an ideal OP-AMP is shown in the Figure.

Which of the following options gives the correct value of the current $I_\chi$ ?