The input signal given to C.E. amplifier having a voltage gain of 126 is $V_i=2 \cos \left(12 t+\frac{\pi}{3}\right)$. The corresponding output signal will be

The figure shows the variation of photocurrent with anode potential for four different radiations. Let $\mathrm{I}_{\mathrm{a}}, \mathrm{I}_{\mathrm{b}}, \mathrm{I}_{\mathrm{c}}$ and $\mathrm{I}_{\mathrm{d}}$ be the intensities for the curves $a, b, c$ and $d$ respectively $\left[f_a, f_b, f_c\right.$ and $f_d$ are frequencies respectively]

When a resistance of $100 \Omega$ is connected in series with a galvanometer of resistance G , its range is V . To double its range a resistance of $1000 \Omega$ is connected in series. The value of G is

The angular separation of the central maximum in the Fraunhofer diffraction pattern is measured. The slit is illuminated by the light of wavelength $6000 \mathop A\limits^o$. If the slit is illuminated by light of another wavelength, the angular separation decreases by $20 \%$. The wavelength of light used is